CA2176767C - Ethylene polymers having enhanced processability - Google Patents
Ethylene polymers having enhanced processability Download PDFInfo
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- CA2176767C CA2176767C CA002176767A CA2176767A CA2176767C CA 2176767 C CA2176767 C CA 2176767C CA 002176767 A CA002176767 A CA 002176767A CA 2176767 A CA2176767 A CA 2176767A CA 2176767 C CA2176767 C CA 2176767C
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
- C08J5/18—Manufacture of films or sheets
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F10/02—Ethene
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F110/02—Ethene
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
- H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
- H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
- H01B3/441—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from alkenes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2323/04—Homopolymers or copolymers of ethene
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S526/00—Synthetic resins or natural rubbers -- part of the class 520 series
- Y10S526/901—Monomer polymerized in vapor state in presence of transition metal containing catalyst
Abstract
An ethylene polymer having a Polydispersity Index of at least about 3.0, a melt index, MI, and a Relaxation Spectrum Index, RSI, such that (RSI)(MI) is greater than about 26 when is about 0.7, and a Crystallizable Chain Length Distribution Index, LW/Ln, less than about 3 is provided. Such ethylene polymer has processability equivalent or superior to even conventional high pressure polyethylene at similar melt index, yet need not be made under high pressure reaction conditions.
Description
D-17341 ~ 21 76767 iYLENE POLYMERS HAVING ENHANCED PROCESSABILITY
This invention relates to ethylene polymers having ~nh~nced proce~sahility, part;cnl~rly extr77tl~hility, and a narrow com~)~omar diætribution that may be advantageously made in a low pressure process. Melt extrusion properties of these ethylene polymers are superior to those of collv~ on~l linear low density polyethylene, and equivalent or superior to those of high ~lessu~e low density polyethylene at ~imil~r melt index.
BACKGROUND
T~inear polyethylene may be readily made in low pressure processes, for instance in gas phase, ~uidized bed reactors. Its merh~nic~l properties, such as st;ffneæs, tensi7,e strength and elongation, are good. Howev~r, its process~hility is deficient. T.ine:~r polyethylene has a ~ntlancy to melt fracture and experience web instability problems such as high neck-in and draw resonance when made into films that are rolled.
- High pressure low density polyethylene, which is highly br~nt~herl, is l,rdfelled to linear low density polyethylene for applications that require processinE ease. High pressure low density polyethylene may, for e~mrle, be readily extruded into films without suffering from melt fracture, overhea~in~ or web instability problems.
However, convçntion~l processes for m~kinE such resins require tubular reactors or autoclaves that operate at e~ ely high pressure (on the order of 30,000 to 45,000 psi) and high temperature (about 200 to 350 C), and are necessarily difficult and expensive to run. In addition, because of its highly branched nature, the merh~nical properties of high pressure low density polyethylene are inferior to those of linear low density polyethylene.
Several workers in the field have ~tt~mpted to address the issue of the poor processability of linear polyethylene by introducing long chain branl~hinE into linear polyethylene. U.S. Patent Nos. 5,272,236;
e d~ rB~6~8-~82~
- d_._~C.~ ~ /
5,380,810; and 5,278,272 to Lai et al.-and PCT Applir~71;nn No. WO
93/08221, a7~ nerl to The Dow Chemic~l CQmr~ny, nes~ihe "sllbst~n~;~llylinear" olefin polymers having ce~ properties le~r7ing to anh~nrer7. process~hililty, including about 0.01 to 3 long chain br~nrhes per 1000 main chain carbon atoms and a molecular-weight distribution of about 1.5 to about 2.5.
- .C imils3rly~ PCT Applic~on No. WO 94/07930 ~RRienr r7. to Egxon Chamir~l Patents Inc. ~lefir-lihes polymers having less than 5 long, linear br~nrhefi per 1000 main chain C~7k)011 atoms with at least some of the br~nrhes having a mr~lec7ll~r weight greater than the critical molecl7l:~r weight for çnt~nglemant of the polymer. WO 94/07930 states that theæe polymers have superior procefis~7~ility as melts a7nd superior marh~7nir~l properties as solids.
U.S. Patent No. 5,374,700 to Tsutsui et al. describes ethylene copolymers said to have narrow co~ os;(~;r~n~l distributiolis and ç~cellr~nt melt tension. The so-called melt flow rates ofthese copolymers are from 0.001 to 50 g/10 min., as measured at a tempelatule of 190 C and a load of 2.16 kg, i.e., t_e same as melt index.
- FinaUy, PCT Applics~t;on No. W094/19381 assigned to Idemitsu Kosan Co., Ltd., relates to an ethylene copolymer derived from - -ethylene and a 3-20 carbon olefin said to have good process~hility and controll~hility wi-th respect to various properties suc_ as density, melting point and cryst~llinity. The copolymer is characterized by 1) the main chain of the polymer does not c~n~in quaternary carbon, 2) the melt-flow activation energy (Ea) is 8-20 kcal/mol, and 3) when the Hll~ns constant k of the copolymer is comp2qred to that of a linear polyethylene having the same limiting viscosity as the copolymer, the viscosity measurement being made in lec~lin at 135 C, the relationship is as follows: 1.12<kVk2~5 (in which kl is the Huggins constant of the copolymer and k2 is that of the linear polyethylene).
A new class of ethylene polymers having excellent process~hililty that is equivalent to or exceeding that o~high pressure D-17341 ~~ 2176767 low density polyel~ylene at ~imilAr melt index has been disc~,veled.
Such ethylene polymers possess a unique set of p- o~el lies not found in prior art polyel~ylene resins.
~UMMARY OF THE INVENTION
The invention provides an ethylene polymer having a Polydis~eldi~y Indeg of at least about 3.0; a melt index, MI, and ~lAlrAhon Spectrum Index, RSI, such that (RSI)(MIa) i8 greater than about 26 when a is about 0.7; and a Cry~t~ Ahle Chain Length Distribution Indeg, LW/Ln, less than about 3. The ethylene polymer is efflciently extruded showing lower head pressure and amperage than are CO11Vel t;onAl linear low density polyethylene or newer commercially available metallocene-made polyethylene. The ethylene polymer, which may be an ethylene homopolymer or interpolymer of ethylene, may be readily fiAh~cAt~1 into a variety of useful articles such as general purpose filmes, clarity films, shrink films, e~usion coA~;n~, wire and cable insnlAt;on and j~.k~t;ng and cross-linke-l, power cable instllA1ion~ molded articles from injection, blow, or rot~on~l mo~ n~ and semicon~tlc~ve insulation and jacketing using methods well known in the art.
BRIEF DESCRIPTION OF THE DRA~1VINGS
Figure 1 is a plot of (RSI)(MI(X) versus melt inde~ (MI) for ethylene polymers of the invention and various other polyethylenes.
Figure 2 is a plot of the Cryst~ ;on Rate Constant (CRC) versus density for ethylene polymers of the invention and various other polyethylenes.
.
DETAILED DESCRIPTION OF THE INVENTION
Ethylene polymers of the invention include ethylene homopolymers, and interpolymers of ethylene and linear or ~ranched higher alpha-olefins cont~inin~ 3 to about 20 carbon atoms, with - densities r~n~in~ from about 0.86 to about 0.95. Suitable higher ~ 21 76767 ,-, -alpha-olçfin~ incl~lde) for ey~ le) propylene, 1-butene, 1-p~ntene, 1-ha~rPna~ 4-methyl-1-p~nte-ne~ '1-octene and 3, 6, 5 t-imPtllyl 1-hP~ane.
Dienes, particularly non-conjll~t~tl 3iPne~, may also be polymeri~e~
with the ethylene. Sllit~hle non-conjl~te~l dienes are linear, br~nrhe-l, or cyclic l~oc~bol- dienes _aving from about'5 to about 20 carbon ntom~. Especially ~refe.led dienes include 1,5-hP~-liane, 5-vinyl-~norbornane, 1,7-oc~-liena and the like. Ethylene polymers also inrlll~es, for ç~s~mple~ ethylene/propylene rubbers (EPR's), ethylene/~ ylene/diene terpolymers (EPDM's) and the like. Aromatic compounds having vinyl lmc~ alion, such as styrene and substituted styrenes, may be included as comQnomers as well. Particularly preferred ethylene polymers comrri~e ethylene and 1 to about 40 percent by weight of one or more comonnm~rs tles~ihed above.
The ethylene polymers have Polydispersity Tn-lices uncorrected for long chain br2~nrhing of at least about 3.0, ~lefelably at least about 4.0, in~lic~t~ng that these ethylene polymers have molecular weight distributions that are advantageously quite broad. The Polydispersity Index (PDI) of a polymer is ~l~finerl as the ratio of the weight average molecular weight of the polymer to the number average molecular weight of the polymer (MV~/lYIn). PDI, uncorrected for long chain br~nrhing, is determined using size exclusion chromatography (SEC)' with a WATERS 150C GPC instrument operating at 140C with 1,2,4-t~i~hloroben~ene at a flow rate of 1 ml/min. The pore size range of the column set provides for a MW separation ~velhlg the 200 to 10,000,000 Daltons range. Nnl;on~l Institute of St~n~rds Technology polyethylene st~nl1~rd NBS 1475 or 1496 is used as the calibration st~n~l~rd to obtain the uncol~ecled ainear polymer assumed) molecular weight distribution.
- The present ethylene polymers have unique rheological properties that impart superior melt strength, shear-t~inning behavior and excellent drawdown en~hling them to process e~ mely easily.
Such enh~nced process~hility ensompasses ease in both egtrusion and fabric?~;on processes, such as in blown film, blow molding, extrusion i~ 21 76767 Co~t;nF and wire and cable egtrusion operations. In particular, the ethylene polymers have melt intl~Yes, MI, and R~ y~ n Spectrum ~nrlaYes~ RSI, guch that, for a given ethylene polymer:
(RSI)(MIa) ~ about 26 when a is about 0.7.~
r~efe~ably, (RSI)(MIa) ? about 30 when a is about 0.7.
In the formulae immediately above, MI is the melt index of the polymer reported as gramS per 10 ~ s~ determined in accordance with ASTM D-1238, condition E, at 190C, and RSI is the Rel~Y~tion Spectrum Index of the polymer in limçnsionless units.
The RSI of the ethylene polymer is dete....; ..e-l by first subjecting the polymer to a shear deform~*on and measuring its response to the deform~1ion using a rheometer. As is known in the art, based on the response of the polymer and the mechanics and geometry of the rheometer used, the rPl~tion modulus G(t) or the dynamic moduli G'(c~) and G"(a)) may be determined as functions of time t or frequency c~, respectively (See J. M. Dealy and K. F. Wissbrun, Melt Rheolo~y andlts Role in Plastics Process;n~, Van Nostrand ~inhold, 1990, pp. 269-297). The m~t.ll~m~tic~l connection between the dynamic and storage moduli is a Fourier transform integral relation, but one set of data may also be calculated from the other using the well known rel~*on spectrum (See S. H. Wasserman, J. Rheology, Vol. 39, pp.
601-625 (1996)). Using a classical mechanical model a discrete re~ tion spectrum consisting of a series of rP~ tjons or "modes, each with a characteristic int~n~ity or "weightn and rel~qtion time may be defined. Using such a spectrum, the moduli are re-expressed as:
~ 21 76767 ~"
G'(a~ gl I + (~, )2 ,=~ 1 + (~i) G(tJ = ~gie~7(-tl~) i=l where N is the nnmhPr of modes and gi and ~ are the weight and time for each of the modes (See J. D. Ferry, Viscoelastic Properties of Polymers, John Wiley & Sons, 1980, pp. 224-263). A re.l~ *on spectrum may be defined for the polymer using so~lw~e such as IRIS(~
rheological software, which is ccmmercially available from IRIS
Development. Once the distribution of modes in the rel~t;on spectrum is calculated, the first and æecon-l momPnte of the distribution, which are analogous to Mn and Mw, the first and second moment~ of the mol`ecular weight distribution, are c~lc~ te~ as follows: .
N /N
gl = ~gi/ ~gi/~i , i=l i=l - -N IN
gll=~gi~ gi - , -i=l i=l RSI is defined as glI/gI-Because RSI is sensitive to such parameters as a polymer's molecular weight distribution, molecular weight, and long chain br~qnçhing, it is a reliable indicator of the process~hlity of a polymer.
The higher the value of RSI, the better the process~hility of the polymer.
In addition, the ethylene polymers have a Cryst~ hle Chain Length Distribution Index, Lw/Ln~ of less than about 3, preferably less than about 2, indicating that they have narrow comonomer ~ 2176767 distributions and thelerole snhst~nt;~l compositional homogeneity.
The Cryst~11i7~hle Chain Length Distribution Index is rl~te~ ;..e-l using Tempeldlula Rising li~lll*nn Fr~ n~1;on (TREF), as ~esrrihed in Wild et al., J. Polymer Sci., Poly. Phys. Ed., Vol. 20, p. 441(1982). A
dilute solution of the ethylene polymer in a solvent such as 1,2,4-trichloroben7.~ne, at 1-4 mg/ml, is lo~le~l at high tempela~ule onto a packed column. The column is then allowed to slowly cool down at 0.1C/min. to ~mhient temre~ alule in a controlled m~nner so that the ethylene polymer is cryst~lli7e-1 onto the p~rkin~ in the order of increasing br~nrhing (or decreasing crystallinity) with the decreasing temperature. The column is then he~te~ in a controlled m~nner at 0.7C/min to above 140C with a constant solvent flow at 2ml/min through the column. The polymer fractions as they are eluted have decreasing br2qnrhing (or increasing cryst~llinity) with the increasing temperature. An infrared conrP.it- alion detector is used to monitor effluent concçn~rations. From the TREF tempelal lre data, the branch frequency may be obtained for a given comonomer. Consequently, the main chain lengths between br~qnrhes~ expressed as Lw and Ln, may be calculated as follows. Lw is the weight average chain length between branches:
LW=~iWiLi and Ln is the number average chain length between branches:
Ln=l/~i(Wi/Li)~
wherein wi is the weight fraction of the polymer component i- having an average backbone chain spacing Li between two adjacent branch points.
Optionally, the narrow comonomer distributions of the ethylene polymers may be characterized using Di~erential Sc~nning Calorimetry (DSC). - With DSC, the melting tempelat.lre of a polymer ~ 21 76767 is measured by a Dilrela,llial ~ F C~lo~im~ter, such as the DSC
2920 commercially av~ hle from Therm~l Analysis Instrum~nts, Inc.
A polymer s~mrle of about 6 mg sealed into an ~l~...-;..~-..- pen is first he~tg~l to 160 C at a rate of 10 Clmin and then cooled to - 20 C also at a rate of 10 C/min. This is followed by a second hea1;n~ to 160 C
at a rate of 10 C/min. The peak mP]t;n~ tempel~l u,a during the secon~ mel1;ng endotherm is recorded as the mel~;ng point ofthe polymer.
The DSC-related properties that the present ethylene polymers preferably have are 1) a DSC Homogeneity Index, DSC-HI, of at least about 7, preferably at least about 9, and 2) a Cryst~ t;oI Rate Constant, CRC, equal to or ~ leater than 1.
The DSC-HI is defined as follows:
DSC-HI=[(Tm, heterog. - Tm)l(Tm~heterog. - Tm~homog.)]lo wherein Tm is the peak melting tempeldlule of the ethylene polymèr and Tm~heterog. and Tm,hl~mog. are peak melting tempela~uas of representative composit;on~lly heterogeneous and compositionally homogeneous polyethylene, respectively, having the same density as the ethylene polymer. The relationships between melting point and density used for the representative heterogeneous and homogeneous polymers are:
homogeneous: Tm = -6023.5 + 12475.3(density) - 6314.6(density)2 heterogeneous: Tm = -49.6 + 189.1(density) The CRC values of the ethylene polymers ~l areldbly are equal to or greater than 1. CRC is a relative measure of the rate of crystallization under a given set of conditions and is defined:
CRC (g/cc) = (density)(Tc/TV2) wherein Tc is the peak cryst~ *on t ~ ,e,dLula of the polymer, and T1/2 is the temrerature at which 50 weight percent of the cryst~ hle fr~c~;onQ. in the polymer have cryst~ e~l. Both Tc and T112 are dete~milled from the recryst~ *nn exotherm obtained with DSC measurem~ntQ of the non-isothermal re~ ~ ~L~ t;on processes.
Polymer density is measured acco~ g to ASTM D-1505.
Another ~ere. l ed characteristic of the present ethylene polymers is that they cont~in at least about 0.3 long chain br~nrhes per 1000 main chain carbon atom. . This further con~ihutes to their excellent process~hility. rrefe. ably, the ethylene polymers cont~in at least about 0.5 long chain br~n~hes per 1000 main chain carbon ~q~om~
More preferably, the ethylene polymers cont~in at least about 0.7 long chain br2qnl~hes per 1000 main chain carbon ~tomc. Long-chain br~nchin~ or LCB is measured by coupled size exclusion chromatography (SEC) with solution vi.ccometry using the Waters 150C GPC instrument (Waters Corporation) with an on-line differential viacQmet~r made by Viscotek Corporation using the same experim~nt~l conditions as described elsewhere for st~n-l~rd.size exclusion chrom~tography. A polyethylene s~n~rd of known molecular weight distribution and intrinsic viscosity in 1,2,4- -trichlorobçn~ene at 140C, such as NBS 1475 or 1496, is used for obt-~inin~ the calibration. The LCB values are derived from the viscosity ratio of the branched polymer to linear polymer of same molecular weight. (See Mirabella, F. M., Jr.; and Wild, L., Polymer Characterization. Amer. Chem. Soc. Symp. Ser. ,227, 1990, p. 23.) An epsilon value of 0.75 is used in rel~in~ the viscosity ratio to the ratio of mean-square radius of gyration of the br~nche-l polymer to linear polymer also at same molecular weight. (See Foster, G. N., MacRury, T. B., Hamielec, A. E., Liquid Chromato~raphy of Polymer and Related Materials II, Ed. - J. Cazes and X Delamere, Marcel Dekker, New York). This ratio of radii of gyration is used in the LCB calculations per the Zimm-Stockmayer relationship (Zimm, B.H. and Stockmayer, W.H., J. Chem. Phys., vol. 17, p. 1301, 1949), as described in Developmen~s in Polymer Characterization - 4, Dawkins, J.V., ed., Applied .~ciçnce, R~rking, 1993.
The ethylene polymers may be made by any ~l,v~.t:Qn~l suspçn~io~, sollltion, slulry or gas phase polymeri~t;on process, using re~ct;on crn~lit;nn~ well known in the art. One reactor or several reactors in series may be employed. Gas phase polymeri~qtion is preferred using one or more f~ e~l bed reactors.
~ C~imil~rly~ catalysts compo~ition~ that may be used to make the ethylene polymers of the illv~-~lion are any of those known for the polymerization of ethylene, such as those co.~-~;sing one or more conventional 7.iegler-Natta catalysts, as well as newer metallocene -catalysts, both of which are well docnm~nte~l in the lite~ e. The use-of a miged catalyst ~y~lem within or ~mong catalyst f~milies may also be used to make the ethylene polymers of the invent;on It has, howev~l-, been discovered that a l,lerelled process for preparing the ethylene polymers co...~ es cont~cting under gas phase polymerization conditions ethylene and optionally a higher alpha-olèfin with a catalyst composition co~ ;sing: a) racemic and meso stèreoisomers of a bridged metallocene catalyst cont~ining two cyclo~lk~-lienyl ligands joined by a hridging linkage and comrlç~e~l to a metal atom, each cy(clo~slk~ ienyl ligand having facial chirality, and b) a cocatalyst selected from the group consisting of methylalllmino~ne and modified methylalllminoxane.
Preferably the metal atom is lilallium, ~ilcollium, or-ha~i......
- More preferably, the metal atom is ~ilco~
Each of the cyclo~lk~ienyl ligands of the bridged metallocene catalyst has facial chirality. Chirality is used to describe asymmetric molecules or li~nll~ whose ~ol- images are non-superimposable (i.e., having "h~n~ellness"). In non-cyclic molecules, there is a chiral center.
In the following case the chiral center is the carbon atom:
F~ ;~,H H~ ~F
C\ B~ \Cl mirror In cyclic ~y~lems a plane of chirality may eYist, giving rise to facial chirality. To illustrate the concept of facial chirality, the indenyl ligand is used as an çY~mple. An indenyl ligand may be viewed as a cyclopentadienyl ligand co~t~ining two substitllents that are connected to form a 6-carbon -ring. An unsubstituted indenyl (i.e., a cyclopentadienyl ligand cont~inin~ only the two substituents that form the 6-member ring) has no chirality. If a chiral substituent is iqtt~rhed to the indenyl ligsln(~, the ligand is described in terms of the chirality of the substituent's chiral center. How~ver, if one or more achiral substituents are ~tt~che-l to the indenyl ligand, and there is no llOl plane of symmetry, the substituted indenyl ligand (the cyclopentadienyl ligand co..t~;..;..g the two substituents connected to form the 6-member ring plus one or more additional achiral substituents) is then said to have facial chirality:
~CH3 ~ --- mirror 2-me~ylindenyl ligand (achiral) CH3 l-"le~l~ylhldenyl ligand (facially prochiral) Thus, the 2-methylindenyl ligand above has no chirality (facial or otherwise) but 1-methylindenyl ligand has facial prochirality.
,~ 2176767 -"
The term facial chirality imrlies a plane of chirality exists which incorporates the indenyl li~nl3, A metal (M) can coordinate to one of the two chiral faces of the l-mell-yli-,denyl li~n~l~ rO....;..~ a basis for discrimin~t;on between the two ~.wl~ l faces. This forms the çnsm~;omers:
", 3+ ~3 M3+ CH3 c ~3 CH3 M3+
~.n~n~iom~,r~
When there are two such ligands in a molecule, each having facial chirality and coortlin~tell to a metal, four possible stereisomers result: the metal can coordinate to the R face of each ligand (R, R') or:
the S face of each ligand (S, S') or it can coordinate to one of each face (R, S' and S, R'), wherein R, R', S, and S' refer to the absolute configurations of the ligands. The R, R' and S, S' stereoisomers are collectively called the racemic stereoisomers, while the R, S' and S, R' stereoisomers are called the meso stereoisomers.
When using the ~lefelred catalyst composition co~ l;sing the bridged metallocene catalyst co~t~ining cyr.lo~lk~-lienyl ligands having facial chirality, it is necessary that both the racemic and meso stereoisomers be present in the catalyst.composition in greater than trivial amounts. r~erelably, both the racemic and meso stereoisomers are present during polymeri~*on in an Amount greater than about 6, more ~l erelably 10, percent by weight of the total anlount of bridged metallocene catalyst co~t~ F cycloalk~lienyl ligands having facial chirality. Such ~mount is indepçn~nt of the ratio of racemic stereoisomer to meso stereoisomer present in the bridged m.etallocene catalyst cont~ining cycloalkadienyl ligands with facial chirality before it is combined with the methylalllmino~ne or modified ~ 21 76767 methylalnminoY~na cocatalyst to form the activated catalyst composition.
In a pl efel~ed embo~im~nt~ the bridged m~t~llocene catalyst c~nnt~inin~ two cycloAlk~dianyl ligands with facial chirality has the form~
RI~R3 ~XI
~ \~
R8~R6 2 R, wherein R1to R8 are the s~me or different monovaIent substituents selected from alkyl, aryl, alkylaryl, arylalkyl, hydrogen, halogen, or hydrocarboxy and any two of Rlto R8 may be connected to form a ring of 4-8 ~t~m~, such that if R1 = R4 then R2 ¢ R3, and if R2 = R3 then R1 ¢ R4, and if Rs = R8 then R6 ¢ R7, and if R6 = R7 then Rs ¢ Rg, the symbol "=" denoting both chemical and stereochemical equivalence;
Q is a divalent substituent selected from alkylidene, dialkylsilylene, dialkylgermylene, and cycloalkylidene;
-, 21 76767 --M is tr~ns~ n metal selecte~l from Group 4, and is ~larelably zilcol~iulll or ha~iu~; and X1 and X2 are the same or dirreldllt, and are monovalent ligands select~fl from alkyl, aryl, alkylaryl, arylalkyl, LyLo~n, halogen, hydroc~l)~,~y, aryloxy, dialkyl~mitlo~ c~b(,~ylato, tl iol~qt~, and thioaryloxy.
The following compounds are.illus~lalive b.ut non~ nil illg ç~mples of useful b~idged metallocene catalysts cor t~inin~ two cycloalkadienyl ligands with facial chirality:
dimethylsilylenebis(indenyl)~colliu~ dichloride, ethylenebis(lin~lenyl)~c~llium dichloride, dimethylsilylenP~his(4~5~6~7-tetraLy~ pnyl)~Lcollium dichloride~
ethylenebis(4,5,6,7-tetrahyL o; . .~l~nyl)~ircolliu~ dichloride, dimethylsilylenebis(2-methylindenyl)~ir~lliul-~ dichloride dimethylsilylenebis~2-methyl-4,5,6,7-tetraLyd~o; .~çny~ colliwi dichloride, methylphenylsilylenebis(2-methylindenyl)~ircoLIium ~lichloride~
dimethylsilylenebis(2,4,7-trimethylindenyi)~ircolli~l-.. dichloride, ethylenebis(2-methylindenyl)~ircolliwn dichloride, ethylenebis(2-methyl-4,5,6,7-tetrahydroin~lenyl)zirconium dichloride, dimethylsilylenebis(2-methylindenyl)~ilcollium dichloride, dimethylsilylçn ahi ~(2-methyl-4-phenylindenyl)~h co~ i rhl oride~ ' dimethylsilylçnP.hiR(2-methyl-4-iso~ro~yli ldenyl)zilco~ irhloride, dimethylsilylenP.hi~(2-methyl-4-n~pht} ylindenyl)~ilcol.~ dichloride, ~limetllylsilylenebis(2-me~ylilldenyl);Gilcolliu~ chloride phçno~i~le, dimethylsilylenebis(2-metllylhldenyl)zi-col~iu~ lliphano~ille, dimethylsilylçnehi~(2-methylindenyl)~,ilcolliu--l bis(dimethyl~mi-le), dimethylsilylenebis(2-methylindenyl)~ircolliulll bis(benzoate), dimethylsilylenebis(2-methylindenyl)zirconillm chloride etho~ide, dimethylsilylenebis(2-methylindenyl)~ilcolliu--l dietl o~i~le, dimethylsilylenebis(2-methylindenyl)zirconium bis(cycinhe~no~ide), tllylsilylçnphi~(2-melhL~ ~denyl)~llL~lllLL c~teGh~ t", ~limPt}lylgilylçnphi~(2~4-~lim-pt~ylcyclopp~nts~ p~ny~ ~ "~ hlor tlimpt~lylsilyle-nphi~(2-methyl-~t-butylcyclopentadienyl)~
hloritle, and ethylPnPbi~(2~4-llimpt~ylcyclopçnt~lie-nyl)~ co lum ~ hloride.
r~efelably, the bridged metallocene catalyst is limPtllylsilylene bis(2-met~l;.-rlPnyl):~ilol~ L dicbloride, which i& defined by the form~ imme~ t,ely above when Rl and R5 are each methyl; R2 and R6 are each hydrogen; R3 and R4 are connects~l to form -CH=CH-CH=CH-, R7 and R8 are connected to form-CH=CH-CH=CH-; Q is dimethylsilylene; M is ~i~Lcom.~ ; and Xl and X2 are each chloride.
The bridged met~llocene catalyst may be made by one of several methods. The method of m~nllf~cture is not critical. For ex~ le, see A. Razavi and J. Ferrara, J. Organomet. Chem., ~, 299 (1992) and K
P. Reddy and J. L. Petersen, Organomet ~llics, ~, 2107 (1989). One method comprises first re~c~ing two equivalents of an optionally substituted cyclopentadiene with a metallic deprot4n~t;ng agent such as an alkyllithium or potassium hydride in an organic solvent such as -tetrahydrofuran, followed by reaction of this solution with a solution of one equivalent of a doubly-halogenated compound such as dichlorodimethyl.~ ne. The resulting ligand is then isolated by conventional methods known to those skilled-in the art (such as dis*ll~t;on or liquid chromatography), reacted with two equiva~ents of a metallic deprot~ ;ng agent as above, and then reacted with one equivalent of a tetr~qchlori-1e of lit~lium, ~hcolli~ , or hafnillm, optionally coor~in~terl with donor ligand molecules such as tetrahydrofuran, in organic solvent. The resulting bridged metallocene catalyst is isolated by methods known to those skilled in the art such as recryst~lli7.n1;0n or sllhlim~tion.
Alternatively, the bridged metallocene catalyst may be produced by first re~c-t;ng one equivalent of an optionally substituted cyclopentadiene with one equivalent of metallic deproto.nating agent in D-17341 ' ~ 2176767 -` -.
an organic solvent as above, followed by re~qc-~;on with one equivalent of a molecule cont~inin~ an lm~ .. ated five-carbon ring to which is ~qtt~-he-l an exocyclic group susceptible to nucleophilic ~tt~qr-k, such as a dialkylfulvene. The reactive solution is next qll~nl~he~ with water -and the li~n~l is i~olat~l by collv~ on~l me~otl~ One bquivalent of the ligand is next re~cte-l with two equivalents of metallic de~lot~....~1;n~ agent as above and the resulting solution is in turn reacted with one equivalent of a tetrachloride of ~ .;. "" ~,~
or hafnium optionally coor~in~ with donor ligand m~lecllles such as tetrahydrofuran, in organic solvent. The resulting bridged metallocene catalyst is isolated by methods known to those skilled in the art.
The cocatalyst is methylalllmino~ne (MAO) or modified methylalllmino~ne (MMAO). Alnmino~nes are well known in the art and comprise oligomeric linear alkyl alllminn~nes represented by the formula:
R~*~ Al~ AIR~ 2 R''** s and oligomeric cyclic alkyl alllmino~nes ofthe formula:
--Al-O-R*** p wherein s is 1~0, ~1 efelably 10-20; p is 3-40, ~1 efe~ ably 3-20; and R***
is an alkyl group conhining 1 to 12 carbon atoms, ~ler~lably methyl or an aryl radical such as a substituted or unsubstituted phenyl or naphthyl radical. In the case of methylalllmino~ne, R*** in the two formulas immediately above is methyl. For modified methylalllmino~ne, R*** is a mi~ of methyl and C2 to C12 alkyl groups, wherein methyl comprises about 20 to about 80 percent by weight of the R*** groups.
~ 21 76767 ~ -AlllminoY~nes may be prepared in a variety of ways. Generally, a ..-; x l ~. . e of linear and cyclic al-lminoY~nes is obt~ine-l in the preparation of ~l~lminl ~nes from, for ~Y~mple, t~ime~ylalv..~;.......
and water. For ~Y~mp~e, an al~ alkyl may be treated with water in the form of a moist solvent. Alternatively, an all...-;..~....
alkyl, such as trimethylall- ..-;...-..-, may be con~qcte~l with a LyJ~al ed salt, such as hydrated ferrous slllf~te The latter method ~...~-l;Res treating a dilute-solution of ~imat~lylal-----;--l---- in, for çY~mrle~
tol lane with a suspçnRiQn offerrous sulfate heptaL~La~e. Itis also possible to form methylalllmino~nes by the reaction of a tetraalkyl-dial~lmino~ne cont~ining C2 or higher alkyl groups with an amount of trimethylalll ...;..~. ..- that is less than a stoichiometric ~cess. The syntl esi~ of methylalllminolrAnes may also be achieved by the re?~-t;on of a trialkyl alllminllm compound or a tetraalkyldialllmino~r~ne con~ining C2 or higher alkyl groups with water to form a polyalkyl al~lmino~na, which is then reacted with trimethylal....-;..~l..-. Further modified methylalllmino~nes, which cont~in both methyl groups and higher alkyl groups, may be synt~esi~e~3 by the re~;on of a polyalkyl alllmino~ne cont~ining C2 or higher alkyl groups with trimethylal.. ;--~.. -- and then with water as disclosed in, for ç~mple, U.S. Patent No. 5,041,584.
The ~mount of bridged metallocene catalyst and cocatalyst usefully employed in the catalyst composition may vary over a wide range. -Preferably, the catalyst composition is present at a concentration sllffiGiant to provide at least about 0.000001, l lere~ably at least about 0.00001, percent by weight of transition metal based on the total weight of ethylene and other monomers. The mole ratio of aluminum atoms col.t~...ed in the methylalllmino~ne or modified methylall1mino~r~ne to metal atoms co~t~ined in the bridged metallocene catalyst is generally in the range of about 2:1 to about 100,000:1, preferably in the range of about 10:1 to about 10,000:1, and most preferably in the range of about 30:1 to about 2,000:1.
D-17341 ! 2 1 7 6 7 6 7 The catalyst compofii*nn may be supported or unsu~l olled. In the case of a bU~)~101 led catalyst composit;nn, the bridged m~hll~cene catalyst and the co~t~lyst may be ~ ts-l in or deposited on the surface of an inert substrate such as silicon (lin~ri~, ~1,.. ~;.. ~ oxide, ma~n~Sium ~liçhlori~le~ poly~lylelle, polyethylene, polyl,lo~ylene, or polycarhon~te, such that the catalyst comro~it;on is between 1 and 90 percent by weight of the total weight of the catalyst c~mrosill;on and the support.
Polymçri~.*on is plerelably con~ cte-1 in the gas phase in a stirred or fllli~ e-l bed reactor, using eq-~ip-.-ant and procedures well known in the art. P~ereldbly, superatmospheric pressures in the range of 1 to 1000 psi, preferably 50 to 400 psi, and most ~lefelably 100 to 300 psi, and temrel dlules in the range of 30 to 130C, ~refelably 65 to 110C are used. Ethylene and other mnnomers~ if used, are cont~ct~-l with an effective amount of catalyæt comrosit;on at a te...~.e. dlu,e and a pressure sllffi~ent to initiate polymeri~tion.
Suitable gas phase polymeri7~t;on re~ction systems co............. l.i;se a - ` :
reactor to which monomeltæ) and catalyst composition may be added, and that cont~in a bed offo....;..~ polyethylene particles. The invention is not limited to any specific type of gas phase re~ct;on system. As an ~mple, a col-vel-tional fluidized bed process is conducted by passing a gaseous stream cont~ining one or more monomers continllously through a fllli~ etl bed reactor under reaction conditions and in the presence of catalyst composition at a velocity sufficient to m~int~in the bed of solid particles in a suspended cl nllition The gaseous stream cont~inin~ unreacted gaseous monomer is withdrawn from the reactor con*nllously, co---~lessed, cooled and recycled into the reactor. Product is withdrawn from the reactor and make-up monomer is added to the recycle stream.
Convention~l additives may be included in the process, provided they do not interfere with the epimeri~tion of racemic and meso stereoisomers of the bridged metallocene catalyst.
When hydrogen is used as a chain transfer agent in the process, it is used in amounts varying between about 0.001 to about 10 moles of hydrogen per mole of total monom~r feed. Also, as desired for tempela~uld control ofthe ~y~ any gas inert to the catalyst composi1;on and re~ ..t~ can also be present in the gas stream.
- OrgAnomPt~llic compounds may be employed as sc~v~.-gin~
agents for poisons to increase the catalyst activity. Fxh...~)les ofthese compounds are metal alkyls, ~lefelably al-~ alkyls, most plefelablytrisobutyl-Ah-~ tri-n-hexylal---..;...-.n Useofsuch scaven~ing agents is well known in the art.
The ethylene polymers may be blended with other polymers and resins as desired using t~chniques known in the art. In All~lit;on) various additives and agents, such as thermo- and photo-o~ t;on st~bili~ers including hindered ph~nolic Ant;o~ nts, hindered amine light st~hili~ers and aryl phosphites or phosphonites, crosslinkers including dicumyl perogide, colorants including ~hboll blacks and and titanium ~lio~ e~ lùbricants including metallic stearates, processing aids including fluoroelastomers, slip agents including ole~mi~le or erllc~mille, film ~n~;hlock or release agents including controlled particle size talc or silica, blovwing agents, flame retardants and other conventional materials may be mi~ed with the ethylene polymer of the invention as desired.
The ethylene polymers of the invention are useful for fabrication into a variety of fini~hed articleæ such as films including clarity films and shrink films, egtrusion co~qt;n~, wire and cable inslll~tion and jacketing, crosslinked power cable insul~l;on, molded articles made by injection nlol~ing~ blow molding, or rotational molding, e~trusions of pipe, tubing, profiles and sheeting, and inslll~1;ng and semiconductive jacketing andlor shields. Methods of m~king such articles are well known in the art.
D-17341 ( ! 21 76767 EXAMPLES
A series of ethylene poly-mers a~ g to the invention (F~mrles 1-35) were C~.K~ d with s~mrles of known polyel~ylene for a variety of ~ el ~ies, in~luding Polydispersity Index (PDI), Cryst~ hle Chain Length Distribution Index (LW/Ln), melt index (MI), 1~ ;on Spectrum Index (RSI), and (RSI)(MIa) when a is about 0.7. In ~ it;on, the long chain br~nrhin~ (LCB), DSC
Homogeneity Index (DSC-HI), and Crys~11i7~ion Rate Const~nt (CRG) were compared.
The ethylene polymers in F~r~mrles 1-35 were made using a 14 inch nomin~l diameter, gas phase, fluidized bed reactor having a bed height of 10 feet. The catalyst composition employed to make each of these F.r~mrles com~l;sed the r~cemic and meso isomers of dimethylsilylenebis(2-melllylhldenyl)zilo~ dichloride and methy1~q1nminoY~ne cocatalyst supported on silica.
Compa alive ~.x~ .1es A-E were Cel ~ AFFINITY Polyolefin Plastomers commercially av~ h~e from The Dow Chemic~q1 Co...~.~..y, as specified in Table 1.
Comparative F,~mples F-J were ce~ EXACT Linear Ethylene Polymers commercially available from E~on Chemical as specified in Table 1.
Comparat*e F~mrles K-M were polyethylene made by high-pressure, free radical polymeri~tion. These low density polyethylenes were produced in a high-pressure, tubular reactor using multiple organic initi~ors~ pressures up to 3000 atmosphere and tempelatul es up to 320C. The process used to produce these high-pressure, low density polyethylenes was aimi1~r to that described in 7.~biRky et al., Polymer, 33, No. 11, 2243, 1992.
Comparative F.~mrles N and O were commercial, linear low-density polyethylenes made by the UNIPOL(~) process (Union Carbide ~orp.) using a gas phase, fluidized bed reactor. These polyethylenes were Ziegler-Natta catalyzed ethylene copolymers of either butene-1 or hexene-1 as described in US Patent No. 4,302,56~. .
D-17341 ~ 2 1 7 6 7 6 7 Compalative F'~mrles P-R were low-density polyel~ylenes made by a gas phase, flt~ e~l bed re~ct;on in a staged reactor configuration using 7.;ç~ler Natta catalyts.
Moleclll~r Wei~ht~ Molec~ r Weight Distribution, and Long Chain Br~nçhin~ (LCB) were tlete, ..-;..ell by size exclusion chromatography as follows. A WATFR~ 150C GPC chrom~raph equipped with mixed-pore size columns for molecular weight measurçman~s and a VISCOTEK 150R v~ meter for on-line viscosi~y measur~m~n~s were employed. For the size exclusion chromatograhy (SEC), a 25 cm long prelimin~ry column from Poly-mer Labs having a 50 A nomin~l pore size, followed-by three 25 cm long Shodex A-80 MlS
(Showa) columns to affect a molecl~l~r weight separation for linear ethylene polymer from about 200 to 10,000,000 Daltons were used.
Both colllmns cont~in porous poly(styrene-divinyl benzene) packing.
1,2,4,-trichloroben7.ene was used as the solvent to prepare the polymer solutions and the chromatographic eluent. All measurçm~n~s were made at a temre, ~Cule of 140 + 0.2C. The analog fiign~lc from the mass and viscosity detectors were collected into a computer system.
The collected data were then processed uæing shnd~rd so~w~e commercially available from several sources (Waters Corporation and Viscotek Corporation) for uncorrected molecular weight distribution.
The calibration uses the broad MWD calibrant method. (See W. W.
Yau, J. J. Kirkland and D. D. Bly, Modern Size-Exclusion Liquid Chromatography, Wiley, 1979, p. 289-313. For the latter, two MW
related statistics such as number and weight average MW values must be known for the polymer calibrant. Based on the MW
calibration, elution volume is converted to molecular weight for the assumed linear ethylene polymer.
A detailed ~ cllR~ion of the methodology of the SEC-Vi~cometry technique and the equations used to collvel l SEC and viscometry data into long-chain br~n~hing and corrected molecular weights is given in the article by Mirabella and Wild referred to above.
DSC and TREF measurements were made as described above.
D-17341 ' 21 76767 eolo~ir~l meaSurçmQn~Q were done via dynamic os~ tory shear experiments con~ ct~ with a new model of the Weissenberg RheogQni- met~ cnmmercially av~ hle from TA Instrllm~ntQ.
EgperimantQ were nin in parallel plate mode under a nitrogen ~q~nosphere at 190C. .~qmple sizes ranged from ap~lox;~n~t~ly 1100 to 1~00 mm and were 4cm in diameter. The frequency sweep experiman~Q covered a frequency range of 0.1 to 100 sec~1 with a 2%
strain ~mplitude. The torque response was converted by the TA
Instrnmant.s rheometAr control sof~w~e to dyn mic moduli and dynamic viscosity data at each frequency. Discrete relaxation spectra were fit to the dynamic moduli data for each sample using the IRIS(~
commercial software p~--.k~ge.
The results, which are reported in Table 1, demonstrate that only the ethylene polymers of the invention eghibit the unique comhin~1;on of a Polydispersity Index of at least about 3.0, a melt index, MI, and a l~el~ t;on Spectrum Index, RSI, such that (RSI)(MIa) is greatèr than about 26 when a is about 0.7, and a - ~
Cryst~ hle Ghain Length Distribution Indeg, LW/Ln, less than about 3. Figure 1 is a plot of the (RSI)(MIa) when a is about 0.7 versus MI data in Table 1.
In addition, only the ethylene polymers of the invention had CRC values equal to or greater than 1. Figure 2 is a plot of the CRC
versus density data in Table 1.
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This invention relates to ethylene polymers having ~nh~nced proce~sahility, part;cnl~rly extr77tl~hility, and a narrow com~)~omar diætribution that may be advantageously made in a low pressure process. Melt extrusion properties of these ethylene polymers are superior to those of collv~ on~l linear low density polyethylene, and equivalent or superior to those of high ~lessu~e low density polyethylene at ~imil~r melt index.
BACKGROUND
T~inear polyethylene may be readily made in low pressure processes, for instance in gas phase, ~uidized bed reactors. Its merh~nic~l properties, such as st;ffneæs, tensi7,e strength and elongation, are good. Howev~r, its process~hility is deficient. T.ine:~r polyethylene has a ~ntlancy to melt fracture and experience web instability problems such as high neck-in and draw resonance when made into films that are rolled.
- High pressure low density polyethylene, which is highly br~nt~herl, is l,rdfelled to linear low density polyethylene for applications that require processinE ease. High pressure low density polyethylene may, for e~mrle, be readily extruded into films without suffering from melt fracture, overhea~in~ or web instability problems.
However, convçntion~l processes for m~kinE such resins require tubular reactors or autoclaves that operate at e~ ely high pressure (on the order of 30,000 to 45,000 psi) and high temperature (about 200 to 350 C), and are necessarily difficult and expensive to run. In addition, because of its highly branched nature, the merh~nical properties of high pressure low density polyethylene are inferior to those of linear low density polyethylene.
Several workers in the field have ~tt~mpted to address the issue of the poor processability of linear polyethylene by introducing long chain branl~hinE into linear polyethylene. U.S. Patent Nos. 5,272,236;
e d~ rB~6~8-~82~
- d_._~C.~ ~ /
5,380,810; and 5,278,272 to Lai et al.-and PCT Applir~71;nn No. WO
93/08221, a7~ nerl to The Dow Chemic~l CQmr~ny, nes~ihe "sllbst~n~;~llylinear" olefin polymers having ce~ properties le~r7ing to anh~nrer7. process~hililty, including about 0.01 to 3 long chain br~nrhes per 1000 main chain carbon atoms and a molecular-weight distribution of about 1.5 to about 2.5.
- .C imils3rly~ PCT Applic~on No. WO 94/07930 ~RRienr r7. to Egxon Chamir~l Patents Inc. ~lefir-lihes polymers having less than 5 long, linear br~nrhefi per 1000 main chain C~7k)011 atoms with at least some of the br~nrhes having a mr~lec7ll~r weight greater than the critical molecl7l:~r weight for çnt~nglemant of the polymer. WO 94/07930 states that theæe polymers have superior procefis~7~ility as melts a7nd superior marh~7nir~l properties as solids.
U.S. Patent No. 5,374,700 to Tsutsui et al. describes ethylene copolymers said to have narrow co~ os;(~;r~n~l distributiolis and ç~cellr~nt melt tension. The so-called melt flow rates ofthese copolymers are from 0.001 to 50 g/10 min., as measured at a tempelatule of 190 C and a load of 2.16 kg, i.e., t_e same as melt index.
- FinaUy, PCT Applics~t;on No. W094/19381 assigned to Idemitsu Kosan Co., Ltd., relates to an ethylene copolymer derived from - -ethylene and a 3-20 carbon olefin said to have good process~hility and controll~hility wi-th respect to various properties suc_ as density, melting point and cryst~llinity. The copolymer is characterized by 1) the main chain of the polymer does not c~n~in quaternary carbon, 2) the melt-flow activation energy (Ea) is 8-20 kcal/mol, and 3) when the Hll~ns constant k of the copolymer is comp2qred to that of a linear polyethylene having the same limiting viscosity as the copolymer, the viscosity measurement being made in lec~lin at 135 C, the relationship is as follows: 1.12<kVk2~5 (in which kl is the Huggins constant of the copolymer and k2 is that of the linear polyethylene).
A new class of ethylene polymers having excellent process~hililty that is equivalent to or exceeding that o~high pressure D-17341 ~~ 2176767 low density polyel~ylene at ~imilAr melt index has been disc~,veled.
Such ethylene polymers possess a unique set of p- o~el lies not found in prior art polyel~ylene resins.
~UMMARY OF THE INVENTION
The invention provides an ethylene polymer having a Polydis~eldi~y Indeg of at least about 3.0; a melt index, MI, and ~lAlrAhon Spectrum Index, RSI, such that (RSI)(MIa) i8 greater than about 26 when a is about 0.7; and a Cry~t~ Ahle Chain Length Distribution Indeg, LW/Ln, less than about 3. The ethylene polymer is efflciently extruded showing lower head pressure and amperage than are CO11Vel t;onAl linear low density polyethylene or newer commercially available metallocene-made polyethylene. The ethylene polymer, which may be an ethylene homopolymer or interpolymer of ethylene, may be readily fiAh~cAt~1 into a variety of useful articles such as general purpose filmes, clarity films, shrink films, e~usion coA~;n~, wire and cable insnlAt;on and j~.k~t;ng and cross-linke-l, power cable instllA1ion~ molded articles from injection, blow, or rot~on~l mo~ n~ and semicon~tlc~ve insulation and jacketing using methods well known in the art.
BRIEF DESCRIPTION OF THE DRA~1VINGS
Figure 1 is a plot of (RSI)(MI(X) versus melt inde~ (MI) for ethylene polymers of the invention and various other polyethylenes.
Figure 2 is a plot of the Cryst~ ;on Rate Constant (CRC) versus density for ethylene polymers of the invention and various other polyethylenes.
.
DETAILED DESCRIPTION OF THE INVENTION
Ethylene polymers of the invention include ethylene homopolymers, and interpolymers of ethylene and linear or ~ranched higher alpha-olefins cont~inin~ 3 to about 20 carbon atoms, with - densities r~n~in~ from about 0.86 to about 0.95. Suitable higher ~ 21 76767 ,-, -alpha-olçfin~ incl~lde) for ey~ le) propylene, 1-butene, 1-p~ntene, 1-ha~rPna~ 4-methyl-1-p~nte-ne~ '1-octene and 3, 6, 5 t-imPtllyl 1-hP~ane.
Dienes, particularly non-conjll~t~tl 3iPne~, may also be polymeri~e~
with the ethylene. Sllit~hle non-conjl~te~l dienes are linear, br~nrhe-l, or cyclic l~oc~bol- dienes _aving from about'5 to about 20 carbon ntom~. Especially ~refe.led dienes include 1,5-hP~-liane, 5-vinyl-~norbornane, 1,7-oc~-liena and the like. Ethylene polymers also inrlll~es, for ç~s~mple~ ethylene/propylene rubbers (EPR's), ethylene/~ ylene/diene terpolymers (EPDM's) and the like. Aromatic compounds having vinyl lmc~ alion, such as styrene and substituted styrenes, may be included as comQnomers as well. Particularly preferred ethylene polymers comrri~e ethylene and 1 to about 40 percent by weight of one or more comonnm~rs tles~ihed above.
The ethylene polymers have Polydispersity Tn-lices uncorrected for long chain br2~nrhing of at least about 3.0, ~lefelably at least about 4.0, in~lic~t~ng that these ethylene polymers have molecular weight distributions that are advantageously quite broad. The Polydispersity Index (PDI) of a polymer is ~l~finerl as the ratio of the weight average molecular weight of the polymer to the number average molecular weight of the polymer (MV~/lYIn). PDI, uncorrected for long chain br~nrhing, is determined using size exclusion chromatography (SEC)' with a WATERS 150C GPC instrument operating at 140C with 1,2,4-t~i~hloroben~ene at a flow rate of 1 ml/min. The pore size range of the column set provides for a MW separation ~velhlg the 200 to 10,000,000 Daltons range. Nnl;on~l Institute of St~n~rds Technology polyethylene st~nl1~rd NBS 1475 or 1496 is used as the calibration st~n~l~rd to obtain the uncol~ecled ainear polymer assumed) molecular weight distribution.
- The present ethylene polymers have unique rheological properties that impart superior melt strength, shear-t~inning behavior and excellent drawdown en~hling them to process e~ mely easily.
Such enh~nced process~hility ensompasses ease in both egtrusion and fabric?~;on processes, such as in blown film, blow molding, extrusion i~ 21 76767 Co~t;nF and wire and cable egtrusion operations. In particular, the ethylene polymers have melt intl~Yes, MI, and R~ y~ n Spectrum ~nrlaYes~ RSI, guch that, for a given ethylene polymer:
(RSI)(MIa) ~ about 26 when a is about 0.7.~
r~efe~ably, (RSI)(MIa) ? about 30 when a is about 0.7.
In the formulae immediately above, MI is the melt index of the polymer reported as gramS per 10 ~ s~ determined in accordance with ASTM D-1238, condition E, at 190C, and RSI is the Rel~Y~tion Spectrum Index of the polymer in limçnsionless units.
The RSI of the ethylene polymer is dete....; ..e-l by first subjecting the polymer to a shear deform~*on and measuring its response to the deform~1ion using a rheometer. As is known in the art, based on the response of the polymer and the mechanics and geometry of the rheometer used, the rPl~tion modulus G(t) or the dynamic moduli G'(c~) and G"(a)) may be determined as functions of time t or frequency c~, respectively (See J. M. Dealy and K. F. Wissbrun, Melt Rheolo~y andlts Role in Plastics Process;n~, Van Nostrand ~inhold, 1990, pp. 269-297). The m~t.ll~m~tic~l connection between the dynamic and storage moduli is a Fourier transform integral relation, but one set of data may also be calculated from the other using the well known rel~*on spectrum (See S. H. Wasserman, J. Rheology, Vol. 39, pp.
601-625 (1996)). Using a classical mechanical model a discrete re~ tion spectrum consisting of a series of rP~ tjons or "modes, each with a characteristic int~n~ity or "weightn and rel~qtion time may be defined. Using such a spectrum, the moduli are re-expressed as:
~ 21 76767 ~"
G'(a~ gl I + (~, )2 ,=~ 1 + (~i) G(tJ = ~gie~7(-tl~) i=l where N is the nnmhPr of modes and gi and ~ are the weight and time for each of the modes (See J. D. Ferry, Viscoelastic Properties of Polymers, John Wiley & Sons, 1980, pp. 224-263). A re.l~ *on spectrum may be defined for the polymer using so~lw~e such as IRIS(~
rheological software, which is ccmmercially available from IRIS
Development. Once the distribution of modes in the rel~t;on spectrum is calculated, the first and æecon-l momPnte of the distribution, which are analogous to Mn and Mw, the first and second moment~ of the mol`ecular weight distribution, are c~lc~ te~ as follows: .
N /N
gl = ~gi/ ~gi/~i , i=l i=l - -N IN
gll=~gi~ gi - , -i=l i=l RSI is defined as glI/gI-Because RSI is sensitive to such parameters as a polymer's molecular weight distribution, molecular weight, and long chain br~qnçhing, it is a reliable indicator of the process~hlity of a polymer.
The higher the value of RSI, the better the process~hility of the polymer.
In addition, the ethylene polymers have a Cryst~ hle Chain Length Distribution Index, Lw/Ln~ of less than about 3, preferably less than about 2, indicating that they have narrow comonomer ~ 2176767 distributions and thelerole snhst~nt;~l compositional homogeneity.
The Cryst~11i7~hle Chain Length Distribution Index is rl~te~ ;..e-l using Tempeldlula Rising li~lll*nn Fr~ n~1;on (TREF), as ~esrrihed in Wild et al., J. Polymer Sci., Poly. Phys. Ed., Vol. 20, p. 441(1982). A
dilute solution of the ethylene polymer in a solvent such as 1,2,4-trichloroben7.~ne, at 1-4 mg/ml, is lo~le~l at high tempela~ule onto a packed column. The column is then allowed to slowly cool down at 0.1C/min. to ~mhient temre~ alule in a controlled m~nner so that the ethylene polymer is cryst~lli7e-1 onto the p~rkin~ in the order of increasing br~nrhing (or decreasing crystallinity) with the decreasing temperature. The column is then he~te~ in a controlled m~nner at 0.7C/min to above 140C with a constant solvent flow at 2ml/min through the column. The polymer fractions as they are eluted have decreasing br2qnrhing (or increasing cryst~llinity) with the increasing temperature. An infrared conrP.it- alion detector is used to monitor effluent concçn~rations. From the TREF tempelal lre data, the branch frequency may be obtained for a given comonomer. Consequently, the main chain lengths between br~qnrhes~ expressed as Lw and Ln, may be calculated as follows. Lw is the weight average chain length between branches:
LW=~iWiLi and Ln is the number average chain length between branches:
Ln=l/~i(Wi/Li)~
wherein wi is the weight fraction of the polymer component i- having an average backbone chain spacing Li between two adjacent branch points.
Optionally, the narrow comonomer distributions of the ethylene polymers may be characterized using Di~erential Sc~nning Calorimetry (DSC). - With DSC, the melting tempelat.lre of a polymer ~ 21 76767 is measured by a Dilrela,llial ~ F C~lo~im~ter, such as the DSC
2920 commercially av~ hle from Therm~l Analysis Instrum~nts, Inc.
A polymer s~mrle of about 6 mg sealed into an ~l~...-;..~-..- pen is first he~tg~l to 160 C at a rate of 10 Clmin and then cooled to - 20 C also at a rate of 10 C/min. This is followed by a second hea1;n~ to 160 C
at a rate of 10 C/min. The peak mP]t;n~ tempel~l u,a during the secon~ mel1;ng endotherm is recorded as the mel~;ng point ofthe polymer.
The DSC-related properties that the present ethylene polymers preferably have are 1) a DSC Homogeneity Index, DSC-HI, of at least about 7, preferably at least about 9, and 2) a Cryst~ t;oI Rate Constant, CRC, equal to or ~ leater than 1.
The DSC-HI is defined as follows:
DSC-HI=[(Tm, heterog. - Tm)l(Tm~heterog. - Tm~homog.)]lo wherein Tm is the peak melting tempeldlule of the ethylene polymèr and Tm~heterog. and Tm,hl~mog. are peak melting tempela~uas of representative composit;on~lly heterogeneous and compositionally homogeneous polyethylene, respectively, having the same density as the ethylene polymer. The relationships between melting point and density used for the representative heterogeneous and homogeneous polymers are:
homogeneous: Tm = -6023.5 + 12475.3(density) - 6314.6(density)2 heterogeneous: Tm = -49.6 + 189.1(density) The CRC values of the ethylene polymers ~l areldbly are equal to or greater than 1. CRC is a relative measure of the rate of crystallization under a given set of conditions and is defined:
CRC (g/cc) = (density)(Tc/TV2) wherein Tc is the peak cryst~ *on t ~ ,e,dLula of the polymer, and T1/2 is the temrerature at which 50 weight percent of the cryst~ hle fr~c~;onQ. in the polymer have cryst~ e~l. Both Tc and T112 are dete~milled from the recryst~ *nn exotherm obtained with DSC measurem~ntQ of the non-isothermal re~ ~ ~L~ t;on processes.
Polymer density is measured acco~ g to ASTM D-1505.
Another ~ere. l ed characteristic of the present ethylene polymers is that they cont~in at least about 0.3 long chain br~nrhes per 1000 main chain carbon atom. . This further con~ihutes to their excellent process~hility. rrefe. ably, the ethylene polymers cont~in at least about 0.5 long chain br~n~hes per 1000 main chain carbon ~q~om~
More preferably, the ethylene polymers cont~in at least about 0.7 long chain br2qnl~hes per 1000 main chain carbon ~tomc. Long-chain br~nchin~ or LCB is measured by coupled size exclusion chromatography (SEC) with solution vi.ccometry using the Waters 150C GPC instrument (Waters Corporation) with an on-line differential viacQmet~r made by Viscotek Corporation using the same experim~nt~l conditions as described elsewhere for st~n-l~rd.size exclusion chrom~tography. A polyethylene s~n~rd of known molecular weight distribution and intrinsic viscosity in 1,2,4- -trichlorobçn~ene at 140C, such as NBS 1475 or 1496, is used for obt-~inin~ the calibration. The LCB values are derived from the viscosity ratio of the branched polymer to linear polymer of same molecular weight. (See Mirabella, F. M., Jr.; and Wild, L., Polymer Characterization. Amer. Chem. Soc. Symp. Ser. ,227, 1990, p. 23.) An epsilon value of 0.75 is used in rel~in~ the viscosity ratio to the ratio of mean-square radius of gyration of the br~nche-l polymer to linear polymer also at same molecular weight. (See Foster, G. N., MacRury, T. B., Hamielec, A. E., Liquid Chromato~raphy of Polymer and Related Materials II, Ed. - J. Cazes and X Delamere, Marcel Dekker, New York). This ratio of radii of gyration is used in the LCB calculations per the Zimm-Stockmayer relationship (Zimm, B.H. and Stockmayer, W.H., J. Chem. Phys., vol. 17, p. 1301, 1949), as described in Developmen~s in Polymer Characterization - 4, Dawkins, J.V., ed., Applied .~ciçnce, R~rking, 1993.
The ethylene polymers may be made by any ~l,v~.t:Qn~l suspçn~io~, sollltion, slulry or gas phase polymeri~t;on process, using re~ct;on crn~lit;nn~ well known in the art. One reactor or several reactors in series may be employed. Gas phase polymeri~qtion is preferred using one or more f~ e~l bed reactors.
~ C~imil~rly~ catalysts compo~ition~ that may be used to make the ethylene polymers of the illv~-~lion are any of those known for the polymerization of ethylene, such as those co.~-~;sing one or more conventional 7.iegler-Natta catalysts, as well as newer metallocene -catalysts, both of which are well docnm~nte~l in the lite~ e. The use-of a miged catalyst ~y~lem within or ~mong catalyst f~milies may also be used to make the ethylene polymers of the invent;on It has, howev~l-, been discovered that a l,lerelled process for preparing the ethylene polymers co...~ es cont~cting under gas phase polymerization conditions ethylene and optionally a higher alpha-olèfin with a catalyst composition co~ ;sing: a) racemic and meso stèreoisomers of a bridged metallocene catalyst cont~ining two cyclo~lk~-lienyl ligands joined by a hridging linkage and comrlç~e~l to a metal atom, each cy(clo~slk~ ienyl ligand having facial chirality, and b) a cocatalyst selected from the group consisting of methylalllmino~ne and modified methylalllminoxane.
Preferably the metal atom is lilallium, ~ilcollium, or-ha~i......
- More preferably, the metal atom is ~ilco~
Each of the cyclo~lk~ienyl ligands of the bridged metallocene catalyst has facial chirality. Chirality is used to describe asymmetric molecules or li~nll~ whose ~ol- images are non-superimposable (i.e., having "h~n~ellness"). In non-cyclic molecules, there is a chiral center.
In the following case the chiral center is the carbon atom:
F~ ;~,H H~ ~F
C\ B~ \Cl mirror In cyclic ~y~lems a plane of chirality may eYist, giving rise to facial chirality. To illustrate the concept of facial chirality, the indenyl ligand is used as an çY~mple. An indenyl ligand may be viewed as a cyclopentadienyl ligand co~t~ining two substitllents that are connected to form a 6-carbon -ring. An unsubstituted indenyl (i.e., a cyclopentadienyl ligand cont~inin~ only the two substituents that form the 6-member ring) has no chirality. If a chiral substituent is iqtt~rhed to the indenyl ligsln(~, the ligand is described in terms of the chirality of the substituent's chiral center. How~ver, if one or more achiral substituents are ~tt~che-l to the indenyl ligand, and there is no llOl plane of symmetry, the substituted indenyl ligand (the cyclopentadienyl ligand co..t~;..;..g the two substituents connected to form the 6-member ring plus one or more additional achiral substituents) is then said to have facial chirality:
~CH3 ~ --- mirror 2-me~ylindenyl ligand (achiral) CH3 l-"le~l~ylhldenyl ligand (facially prochiral) Thus, the 2-methylindenyl ligand above has no chirality (facial or otherwise) but 1-methylindenyl ligand has facial prochirality.
,~ 2176767 -"
The term facial chirality imrlies a plane of chirality exists which incorporates the indenyl li~nl3, A metal (M) can coordinate to one of the two chiral faces of the l-mell-yli-,denyl li~n~l~ rO....;..~ a basis for discrimin~t;on between the two ~.wl~ l faces. This forms the çnsm~;omers:
", 3+ ~3 M3+ CH3 c ~3 CH3 M3+
~.n~n~iom~,r~
When there are two such ligands in a molecule, each having facial chirality and coortlin~tell to a metal, four possible stereisomers result: the metal can coordinate to the R face of each ligand (R, R') or:
the S face of each ligand (S, S') or it can coordinate to one of each face (R, S' and S, R'), wherein R, R', S, and S' refer to the absolute configurations of the ligands. The R, R' and S, S' stereoisomers are collectively called the racemic stereoisomers, while the R, S' and S, R' stereoisomers are called the meso stereoisomers.
When using the ~lefelred catalyst composition co~ l;sing the bridged metallocene catalyst co~t~ining cyr.lo~lk~-lienyl ligands having facial chirality, it is necessary that both the racemic and meso stereoisomers be present in the catalyst.composition in greater than trivial amounts. r~erelably, both the racemic and meso stereoisomers are present during polymeri~*on in an Amount greater than about 6, more ~l erelably 10, percent by weight of the total anlount of bridged metallocene catalyst co~t~ F cycloalk~lienyl ligands having facial chirality. Such ~mount is indepçn~nt of the ratio of racemic stereoisomer to meso stereoisomer present in the bridged m.etallocene catalyst cont~ining cycloalkadienyl ligands with facial chirality before it is combined with the methylalllmino~ne or modified ~ 21 76767 methylalnminoY~na cocatalyst to form the activated catalyst composition.
In a pl efel~ed embo~im~nt~ the bridged m~t~llocene catalyst c~nnt~inin~ two cycloAlk~dianyl ligands with facial chirality has the form~
RI~R3 ~XI
~ \~
R8~R6 2 R, wherein R1to R8 are the s~me or different monovaIent substituents selected from alkyl, aryl, alkylaryl, arylalkyl, hydrogen, halogen, or hydrocarboxy and any two of Rlto R8 may be connected to form a ring of 4-8 ~t~m~, such that if R1 = R4 then R2 ¢ R3, and if R2 = R3 then R1 ¢ R4, and if Rs = R8 then R6 ¢ R7, and if R6 = R7 then Rs ¢ Rg, the symbol "=" denoting both chemical and stereochemical equivalence;
Q is a divalent substituent selected from alkylidene, dialkylsilylene, dialkylgermylene, and cycloalkylidene;
-, 21 76767 --M is tr~ns~ n metal selecte~l from Group 4, and is ~larelably zilcol~iulll or ha~iu~; and X1 and X2 are the same or dirreldllt, and are monovalent ligands select~fl from alkyl, aryl, alkylaryl, arylalkyl, LyLo~n, halogen, hydroc~l)~,~y, aryloxy, dialkyl~mitlo~ c~b(,~ylato, tl iol~qt~, and thioaryloxy.
The following compounds are.illus~lalive b.ut non~ nil illg ç~mples of useful b~idged metallocene catalysts cor t~inin~ two cycloalkadienyl ligands with facial chirality:
dimethylsilylenebis(indenyl)~colliu~ dichloride, ethylenebis(lin~lenyl)~c~llium dichloride, dimethylsilylenP~his(4~5~6~7-tetraLy~ pnyl)~Lcollium dichloride~
ethylenebis(4,5,6,7-tetrahyL o; . .~l~nyl)~ircolliu~ dichloride, dimethylsilylenebis(2-methylindenyl)~ir~lliul-~ dichloride dimethylsilylenebis~2-methyl-4,5,6,7-tetraLyd~o; .~çny~ colliwi dichloride, methylphenylsilylenebis(2-methylindenyl)~ircoLIium ~lichloride~
dimethylsilylenebis(2,4,7-trimethylindenyi)~ircolli~l-.. dichloride, ethylenebis(2-methylindenyl)~ircolliwn dichloride, ethylenebis(2-methyl-4,5,6,7-tetrahydroin~lenyl)zirconium dichloride, dimethylsilylenebis(2-methylindenyl)~ilcollium dichloride, dimethylsilylçn ahi ~(2-methyl-4-phenylindenyl)~h co~ i rhl oride~ ' dimethylsilylçnP.hiR(2-methyl-4-iso~ro~yli ldenyl)zilco~ irhloride, dimethylsilylenP.hi~(2-methyl-4-n~pht} ylindenyl)~ilcol.~ dichloride, ~limetllylsilylenebis(2-me~ylilldenyl);Gilcolliu~ chloride phçno~i~le, dimethylsilylenebis(2-metllylhldenyl)zi-col~iu~ lliphano~ille, dimethylsilylçnehi~(2-methylindenyl)~,ilcolliu--l bis(dimethyl~mi-le), dimethylsilylenebis(2-methylindenyl)~ircolliulll bis(benzoate), dimethylsilylenebis(2-methylindenyl)zirconillm chloride etho~ide, dimethylsilylenebis(2-methylindenyl)~ilcolliu--l dietl o~i~le, dimethylsilylenebis(2-methylindenyl)zirconium bis(cycinhe~no~ide), tllylsilylçnphi~(2-melhL~ ~denyl)~llL~lllLL c~teGh~ t", ~limPt}lylgilylçnphi~(2~4-~lim-pt~ylcyclopp~nts~ p~ny~ ~ "~ hlor tlimpt~lylsilyle-nphi~(2-methyl-~t-butylcyclopentadienyl)~
hloritle, and ethylPnPbi~(2~4-llimpt~ylcyclopçnt~lie-nyl)~ co lum ~ hloride.
r~efelably, the bridged metallocene catalyst is limPtllylsilylene bis(2-met~l;.-rlPnyl):~ilol~ L dicbloride, which i& defined by the form~ imme~ t,ely above when Rl and R5 are each methyl; R2 and R6 are each hydrogen; R3 and R4 are connects~l to form -CH=CH-CH=CH-, R7 and R8 are connected to form-CH=CH-CH=CH-; Q is dimethylsilylene; M is ~i~Lcom.~ ; and Xl and X2 are each chloride.
The bridged met~llocene catalyst may be made by one of several methods. The method of m~nllf~cture is not critical. For ex~ le, see A. Razavi and J. Ferrara, J. Organomet. Chem., ~, 299 (1992) and K
P. Reddy and J. L. Petersen, Organomet ~llics, ~, 2107 (1989). One method comprises first re~c~ing two equivalents of an optionally substituted cyclopentadiene with a metallic deprot4n~t;ng agent such as an alkyllithium or potassium hydride in an organic solvent such as -tetrahydrofuran, followed by reaction of this solution with a solution of one equivalent of a doubly-halogenated compound such as dichlorodimethyl.~ ne. The resulting ligand is then isolated by conventional methods known to those skilled-in the art (such as dis*ll~t;on or liquid chromatography), reacted with two equiva~ents of a metallic deprot~ ;ng agent as above, and then reacted with one equivalent of a tetr~qchlori-1e of lit~lium, ~hcolli~ , or hafnillm, optionally coor~in~terl with donor ligand molecules such as tetrahydrofuran, in organic solvent. The resulting bridged metallocene catalyst is isolated by methods known to those skilled in the art such as recryst~lli7.n1;0n or sllhlim~tion.
Alternatively, the bridged metallocene catalyst may be produced by first re~c-t;ng one equivalent of an optionally substituted cyclopentadiene with one equivalent of metallic deproto.nating agent in D-17341 ' ~ 2176767 -` -.
an organic solvent as above, followed by re~qc-~;on with one equivalent of a molecule cont~inin~ an lm~ .. ated five-carbon ring to which is ~qtt~-he-l an exocyclic group susceptible to nucleophilic ~tt~qr-k, such as a dialkylfulvene. The reactive solution is next qll~nl~he~ with water -and the li~n~l is i~olat~l by collv~ on~l me~otl~ One bquivalent of the ligand is next re~cte-l with two equivalents of metallic de~lot~....~1;n~ agent as above and the resulting solution is in turn reacted with one equivalent of a tetrachloride of ~ .;. "" ~,~
or hafnium optionally coor~in~ with donor ligand m~lecllles such as tetrahydrofuran, in organic solvent. The resulting bridged metallocene catalyst is isolated by methods known to those skilled in the art.
The cocatalyst is methylalllmino~ne (MAO) or modified methylalllmino~ne (MMAO). Alnmino~nes are well known in the art and comprise oligomeric linear alkyl alllminn~nes represented by the formula:
R~*~ Al~ AIR~ 2 R''** s and oligomeric cyclic alkyl alllmino~nes ofthe formula:
--Al-O-R*** p wherein s is 1~0, ~1 efelably 10-20; p is 3-40, ~1 efe~ ably 3-20; and R***
is an alkyl group conhining 1 to 12 carbon atoms, ~ler~lably methyl or an aryl radical such as a substituted or unsubstituted phenyl or naphthyl radical. In the case of methylalllmino~ne, R*** in the two formulas immediately above is methyl. For modified methylalllmino~ne, R*** is a mi~ of methyl and C2 to C12 alkyl groups, wherein methyl comprises about 20 to about 80 percent by weight of the R*** groups.
~ 21 76767 ~ -AlllminoY~nes may be prepared in a variety of ways. Generally, a ..-; x l ~. . e of linear and cyclic al-lminoY~nes is obt~ine-l in the preparation of ~l~lminl ~nes from, for ~Y~mple, t~ime~ylalv..~;.......
and water. For ~Y~mp~e, an al~ alkyl may be treated with water in the form of a moist solvent. Alternatively, an all...-;..~....
alkyl, such as trimethylall- ..-;...-..-, may be con~qcte~l with a LyJ~al ed salt, such as hydrated ferrous slllf~te The latter method ~...~-l;Res treating a dilute-solution of ~imat~lylal-----;--l---- in, for çY~mrle~
tol lane with a suspçnRiQn offerrous sulfate heptaL~La~e. Itis also possible to form methylalllmino~nes by the reaction of a tetraalkyl-dial~lmino~ne cont~ining C2 or higher alkyl groups with an amount of trimethylalll ...;..~. ..- that is less than a stoichiometric ~cess. The syntl esi~ of methylalllminolrAnes may also be achieved by the re?~-t;on of a trialkyl alllminllm compound or a tetraalkyldialllmino~r~ne con~ining C2 or higher alkyl groups with water to form a polyalkyl al~lmino~na, which is then reacted with trimethylal....-;..~l..-. Further modified methylalllmino~nes, which cont~in both methyl groups and higher alkyl groups, may be synt~esi~e~3 by the re~;on of a polyalkyl alllmino~ne cont~ining C2 or higher alkyl groups with trimethylal.. ;--~.. -- and then with water as disclosed in, for ç~mple, U.S. Patent No. 5,041,584.
The ~mount of bridged metallocene catalyst and cocatalyst usefully employed in the catalyst composition may vary over a wide range. -Preferably, the catalyst composition is present at a concentration sllffiGiant to provide at least about 0.000001, l lere~ably at least about 0.00001, percent by weight of transition metal based on the total weight of ethylene and other monomers. The mole ratio of aluminum atoms col.t~...ed in the methylalllmino~ne or modified methylall1mino~r~ne to metal atoms co~t~ined in the bridged metallocene catalyst is generally in the range of about 2:1 to about 100,000:1, preferably in the range of about 10:1 to about 10,000:1, and most preferably in the range of about 30:1 to about 2,000:1.
D-17341 ! 2 1 7 6 7 6 7 The catalyst compofii*nn may be supported or unsu~l olled. In the case of a bU~)~101 led catalyst composit;nn, the bridged m~hll~cene catalyst and the co~t~lyst may be ~ ts-l in or deposited on the surface of an inert substrate such as silicon (lin~ri~, ~1,.. ~;.. ~ oxide, ma~n~Sium ~liçhlori~le~ poly~lylelle, polyethylene, polyl,lo~ylene, or polycarhon~te, such that the catalyst comro~it;on is between 1 and 90 percent by weight of the total weight of the catalyst c~mrosill;on and the support.
Polymçri~.*on is plerelably con~ cte-1 in the gas phase in a stirred or fllli~ e-l bed reactor, using eq-~ip-.-ant and procedures well known in the art. P~ereldbly, superatmospheric pressures in the range of 1 to 1000 psi, preferably 50 to 400 psi, and most ~lefelably 100 to 300 psi, and temrel dlules in the range of 30 to 130C, ~refelably 65 to 110C are used. Ethylene and other mnnomers~ if used, are cont~ct~-l with an effective amount of catalyæt comrosit;on at a te...~.e. dlu,e and a pressure sllffi~ent to initiate polymeri~tion.
Suitable gas phase polymeri7~t;on re~ction systems co............. l.i;se a - ` :
reactor to which monomeltæ) and catalyst composition may be added, and that cont~in a bed offo....;..~ polyethylene particles. The invention is not limited to any specific type of gas phase re~ct;on system. As an ~mple, a col-vel-tional fluidized bed process is conducted by passing a gaseous stream cont~ining one or more monomers continllously through a fllli~ etl bed reactor under reaction conditions and in the presence of catalyst composition at a velocity sufficient to m~int~in the bed of solid particles in a suspended cl nllition The gaseous stream cont~inin~ unreacted gaseous monomer is withdrawn from the reactor con*nllously, co---~lessed, cooled and recycled into the reactor. Product is withdrawn from the reactor and make-up monomer is added to the recycle stream.
Convention~l additives may be included in the process, provided they do not interfere with the epimeri~tion of racemic and meso stereoisomers of the bridged metallocene catalyst.
When hydrogen is used as a chain transfer agent in the process, it is used in amounts varying between about 0.001 to about 10 moles of hydrogen per mole of total monom~r feed. Also, as desired for tempela~uld control ofthe ~y~ any gas inert to the catalyst composi1;on and re~ ..t~ can also be present in the gas stream.
- OrgAnomPt~llic compounds may be employed as sc~v~.-gin~
agents for poisons to increase the catalyst activity. Fxh...~)les ofthese compounds are metal alkyls, ~lefelably al-~ alkyls, most plefelablytrisobutyl-Ah-~ tri-n-hexylal---..;...-.n Useofsuch scaven~ing agents is well known in the art.
The ethylene polymers may be blended with other polymers and resins as desired using t~chniques known in the art. In All~lit;on) various additives and agents, such as thermo- and photo-o~ t;on st~bili~ers including hindered ph~nolic Ant;o~ nts, hindered amine light st~hili~ers and aryl phosphites or phosphonites, crosslinkers including dicumyl perogide, colorants including ~hboll blacks and and titanium ~lio~ e~ lùbricants including metallic stearates, processing aids including fluoroelastomers, slip agents including ole~mi~le or erllc~mille, film ~n~;hlock or release agents including controlled particle size talc or silica, blovwing agents, flame retardants and other conventional materials may be mi~ed with the ethylene polymer of the invention as desired.
The ethylene polymers of the invention are useful for fabrication into a variety of fini~hed articleæ such as films including clarity films and shrink films, egtrusion co~qt;n~, wire and cable inslll~tion and jacketing, crosslinked power cable insul~l;on, molded articles made by injection nlol~ing~ blow molding, or rotational molding, e~trusions of pipe, tubing, profiles and sheeting, and inslll~1;ng and semiconductive jacketing andlor shields. Methods of m~king such articles are well known in the art.
D-17341 ( ! 21 76767 EXAMPLES
A series of ethylene poly-mers a~ g to the invention (F~mrles 1-35) were C~.K~ d with s~mrles of known polyel~ylene for a variety of ~ el ~ies, in~luding Polydispersity Index (PDI), Cryst~ hle Chain Length Distribution Index (LW/Ln), melt index (MI), 1~ ;on Spectrum Index (RSI), and (RSI)(MIa) when a is about 0.7. In ~ it;on, the long chain br~nrhin~ (LCB), DSC
Homogeneity Index (DSC-HI), and Crys~11i7~ion Rate Const~nt (CRG) were compared.
The ethylene polymers in F~r~mrles 1-35 were made using a 14 inch nomin~l diameter, gas phase, fluidized bed reactor having a bed height of 10 feet. The catalyst composition employed to make each of these F.r~mrles com~l;sed the r~cemic and meso isomers of dimethylsilylenebis(2-melllylhldenyl)zilo~ dichloride and methy1~q1nminoY~ne cocatalyst supported on silica.
Compa alive ~.x~ .1es A-E were Cel ~ AFFINITY Polyolefin Plastomers commercially av~ h~e from The Dow Chemic~q1 Co...~.~..y, as specified in Table 1.
Comparative F,~mples F-J were ce~ EXACT Linear Ethylene Polymers commercially available from E~on Chemical as specified in Table 1.
Comparat*e F~mrles K-M were polyethylene made by high-pressure, free radical polymeri~tion. These low density polyethylenes were produced in a high-pressure, tubular reactor using multiple organic initi~ors~ pressures up to 3000 atmosphere and tempelatul es up to 320C. The process used to produce these high-pressure, low density polyethylenes was aimi1~r to that described in 7.~biRky et al., Polymer, 33, No. 11, 2243, 1992.
Comparative F.~mrles N and O were commercial, linear low-density polyethylenes made by the UNIPOL(~) process (Union Carbide ~orp.) using a gas phase, fluidized bed reactor. These polyethylenes were Ziegler-Natta catalyzed ethylene copolymers of either butene-1 or hexene-1 as described in US Patent No. 4,302,56~. .
D-17341 ~ 2 1 7 6 7 6 7 Compalative F'~mrles P-R were low-density polyel~ylenes made by a gas phase, flt~ e~l bed re~ct;on in a staged reactor configuration using 7.;ç~ler Natta catalyts.
Moleclll~r Wei~ht~ Molec~ r Weight Distribution, and Long Chain Br~nçhin~ (LCB) were tlete, ..-;..ell by size exclusion chromatography as follows. A WATFR~ 150C GPC chrom~raph equipped with mixed-pore size columns for molecular weight measurçman~s and a VISCOTEK 150R v~ meter for on-line viscosi~y measur~m~n~s were employed. For the size exclusion chromatograhy (SEC), a 25 cm long prelimin~ry column from Poly-mer Labs having a 50 A nomin~l pore size, followed-by three 25 cm long Shodex A-80 MlS
(Showa) columns to affect a molecl~l~r weight separation for linear ethylene polymer from about 200 to 10,000,000 Daltons were used.
Both colllmns cont~in porous poly(styrene-divinyl benzene) packing.
1,2,4,-trichloroben7.ene was used as the solvent to prepare the polymer solutions and the chromatographic eluent. All measurçm~n~s were made at a temre, ~Cule of 140 + 0.2C. The analog fiign~lc from the mass and viscosity detectors were collected into a computer system.
The collected data were then processed uæing shnd~rd so~w~e commercially available from several sources (Waters Corporation and Viscotek Corporation) for uncorrected molecular weight distribution.
The calibration uses the broad MWD calibrant method. (See W. W.
Yau, J. J. Kirkland and D. D. Bly, Modern Size-Exclusion Liquid Chromatography, Wiley, 1979, p. 289-313. For the latter, two MW
related statistics such as number and weight average MW values must be known for the polymer calibrant. Based on the MW
calibration, elution volume is converted to molecular weight for the assumed linear ethylene polymer.
A detailed ~ cllR~ion of the methodology of the SEC-Vi~cometry technique and the equations used to collvel l SEC and viscometry data into long-chain br~n~hing and corrected molecular weights is given in the article by Mirabella and Wild referred to above.
DSC and TREF measurements were made as described above.
D-17341 ' 21 76767 eolo~ir~l meaSurçmQn~Q were done via dynamic os~ tory shear experiments con~ ct~ with a new model of the Weissenberg RheogQni- met~ cnmmercially av~ hle from TA Instrllm~ntQ.
EgperimantQ were nin in parallel plate mode under a nitrogen ~q~nosphere at 190C. .~qmple sizes ranged from ap~lox;~n~t~ly 1100 to 1~00 mm and were 4cm in diameter. The frequency sweep experiman~Q covered a frequency range of 0.1 to 100 sec~1 with a 2%
strain ~mplitude. The torque response was converted by the TA
Instrnmant.s rheometAr control sof~w~e to dyn mic moduli and dynamic viscosity data at each frequency. Discrete relaxation spectra were fit to the dynamic moduli data for each sample using the IRIS(~
commercial software p~--.k~ge.
The results, which are reported in Table 1, demonstrate that only the ethylene polymers of the invention eghibit the unique comhin~1;on of a Polydispersity Index of at least about 3.0, a melt index, MI, and a l~el~ t;on Spectrum Index, RSI, such that (RSI)(MIa) is greatèr than about 26 when a is about 0.7, and a - ~
Cryst~ hle Ghain Length Distribution Indeg, LW/Ln, less than about 3. Figure 1 is a plot of the (RSI)(MIa) when a is about 0.7 versus MI data in Table 1.
In addition, only the ethylene polymers of the invention had CRC values equal to or greater than 1. Figure 2 is a plot of the CRC
versus density data in Table 1.
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min. sic Vis- per cosity 1000C
(dL/g) P Staged 0.80 0.00 0.9230 l~e~ctor PE
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a Refe~ g now to Table 2, the ethylene polymers of F,~mples 1-12, as well as Comp~al,ive F.~mrles A, C, E, F, L, M, O and P were each comr~red for their extr~ hility under blown film processin~
com~lit;on.~.
The ethylene polymers of the illv~lllion were each dry blended with 1000 ppm IRGANOX B-900 (Ciba-Geigy Corporation) and compounded in a 1-V2 inch Killion E2~truder with a standar~ LLDPE
mi~ing screw (30/1 length to di~meter) at a rate of 40 lb~hr (~90 rpm) with a set die tempel~lur~ of 410F. The pelleted ethylene polymers and the Comparative F.~mple polyethylenes were e~truded into blown films using typical operating conllit;on~. The blown film e~trusion equipment consisted of a 1 V2 inch diameter Sterling extruder equipped with 24:1 L/D, general purpose LLDPE screw (constant pitch, decreasing depth, M~ lo~ mi~nn~-head screw) and a spiral pin die.
The specifics of the dies used and the extrusion speed and temperature conditions were as follows:
F,~mples Screw Speed Temperature Profile. F ;~
1-12, M 98 rpm 350 flat temp. profile 2.2 inch spiral die, 30 mil die gap, with 2.14 inch die diameter and 0.312 inch die length L 90 rpm 410, 425,460, 460,460 2.2 inch spiral 460,460 die, 30 mil die gap, with 2.14 inch die diameter and 0.312 inch die length A, C, E, F, 90 rpm 380,380, 385, 390,400 3 inch spiral die, &N 400,400 80 mil die gap, with 2.84 inch die diameter and 1.2~inch die length D-17341 ; 2176767 -- -.
P 90 rpm 380, 380, 385, 390, 400, 2.2 inch spiral 400, 400 die, 30 mil die gap, with 2.14 inch die diameter and 0.312 inch die length-Table 2 show the head pl~es;:iule and amperage that was required to extrude each of the resins tested, as well as the head pressure and amperage norm~ ed with respect to the die rate, so that direct comparisons may be made. The norm~li7.ed data in Table 2 shows that the head pressures and amps required in extruding the ethylene polymers of the invention were much less than those needed to extrude the Comparat*e F.~mples when compared at .simil~r melt index.
Further, the ethylene polymers of the invention showed excellent drawdown and extrusion ease comp~red to high pressure, low density polyethylene.
-Table 2 - Blown Film Proces.~in~
F.~mrles Polymer Head Amps Die Press~ Amp/
Pressure Rate DR DR
lbs~hrrm Invention 1390.0 6.00 5.40 257.41 1.11 2 Invention 1200.0 7.20 6.60 181.82 1.09 3 Invention 1390.0 6.00 5.10 272.55 1.18 4 Invention 1390.0 7.60 6.50 213.85 1.15 Invention 1550.0 8.20 6.50 238.46 1.26 6 Invention 1500.0 7.70 6.50 230.77 1.18 7 Invention 1700.0 7.50 6.50 261.54 1.15-8 Invention 1500.0 7.90 6.60 227.27 1.20 9 Invention 1700.0 7.20 6.30 269.84 1.14 Invention 1590.0 6.20 5.40 294.44 1.15 11 Invention 1450.0 7.10 6.70 216.42 1.06 12 Invention 2100.0 9.80 6.60 318.18 L48 A AFFINITY 1900.0 12.2000 3.5000 542.86 3.49 C AFFINITY 1960.0 11.6000 2.8600 685.31 4.06 E AFFINITY 1960.0 11.7000 2.9200 671.23 4.01 F EXACT-2010 2560.0 17.2000 3.6300 705.23 4.74 L HP-LDPE 2100.0 8.2000 5.9000 355.93 1.39 M HP-LDPE 2000.0 7.9000 5.9000 338.98 1.34 - N LLDPE
O LLDPE 2650.0 14.2000 3.3900 781.il 4.19 P Staged 2200.0 9.0000 5.7300 383.94 1.57 Reactor PE
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min. sic Vis- per cosity 1000C
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a Refe~ g now to Table 2, the ethylene polymers of F,~mples 1-12, as well as Comp~al,ive F.~mrles A, C, E, F, L, M, O and P were each comr~red for their extr~ hility under blown film processin~
com~lit;on.~.
The ethylene polymers of the illv~lllion were each dry blended with 1000 ppm IRGANOX B-900 (Ciba-Geigy Corporation) and compounded in a 1-V2 inch Killion E2~truder with a standar~ LLDPE
mi~ing screw (30/1 length to di~meter) at a rate of 40 lb~hr (~90 rpm) with a set die tempel~lur~ of 410F. The pelleted ethylene polymers and the Comparative F.~mple polyethylenes were e~truded into blown films using typical operating conllit;on~. The blown film e~trusion equipment consisted of a 1 V2 inch diameter Sterling extruder equipped with 24:1 L/D, general purpose LLDPE screw (constant pitch, decreasing depth, M~ lo~ mi~nn~-head screw) and a spiral pin die.
The specifics of the dies used and the extrusion speed and temperature conditions were as follows:
F,~mples Screw Speed Temperature Profile. F ;~
1-12, M 98 rpm 350 flat temp. profile 2.2 inch spiral die, 30 mil die gap, with 2.14 inch die diameter and 0.312 inch die length L 90 rpm 410, 425,460, 460,460 2.2 inch spiral 460,460 die, 30 mil die gap, with 2.14 inch die diameter and 0.312 inch die length A, C, E, F, 90 rpm 380,380, 385, 390,400 3 inch spiral die, &N 400,400 80 mil die gap, with 2.84 inch die diameter and 1.2~inch die length D-17341 ; 2176767 -- -.
P 90 rpm 380, 380, 385, 390, 400, 2.2 inch spiral 400, 400 die, 30 mil die gap, with 2.14 inch die diameter and 0.312 inch die length-Table 2 show the head pl~es;:iule and amperage that was required to extrude each of the resins tested, as well as the head pressure and amperage norm~ ed with respect to the die rate, so that direct comparisons may be made. The norm~li7.ed data in Table 2 shows that the head pressures and amps required in extruding the ethylene polymers of the invention were much less than those needed to extrude the Comparat*e F.~mples when compared at .simil~r melt index.
Further, the ethylene polymers of the invention showed excellent drawdown and extrusion ease comp~red to high pressure, low density polyethylene.
-Table 2 - Blown Film Proces.~in~
F.~mrles Polymer Head Amps Die Press~ Amp/
Pressure Rate DR DR
lbs~hrrm Invention 1390.0 6.00 5.40 257.41 1.11 2 Invention 1200.0 7.20 6.60 181.82 1.09 3 Invention 1390.0 6.00 5.10 272.55 1.18 4 Invention 1390.0 7.60 6.50 213.85 1.15 Invention 1550.0 8.20 6.50 238.46 1.26 6 Invention 1500.0 7.70 6.50 230.77 1.18 7 Invention 1700.0 7.50 6.50 261.54 1.15-8 Invention 1500.0 7.90 6.60 227.27 1.20 9 Invention 1700.0 7.20 6.30 269.84 1.14 Invention 1590.0 6.20 5.40 294.44 1.15 11 Invention 1450.0 7.10 6.70 216.42 1.06 12 Invention 2100.0 9.80 6.60 318.18 L48 A AFFINITY 1900.0 12.2000 3.5000 542.86 3.49 C AFFINITY 1960.0 11.6000 2.8600 685.31 4.06 E AFFINITY 1960.0 11.7000 2.9200 671.23 4.01 F EXACT-2010 2560.0 17.2000 3.6300 705.23 4.74 L HP-LDPE 2100.0 8.2000 5.9000 355.93 1.39 M HP-LDPE 2000.0 7.9000 5.9000 338.98 1.34 - N LLDPE
O LLDPE 2650.0 14.2000 3.3900 781.il 4.19 P Staged 2200.0 9.0000 5.7300 383.94 1.57 Reactor PE
Claims (19)
1. An ethylene polymer having:
a Polydispersity Index of at least about 3.0;
a melt index, MI, and a Relaxation Spectrum Index, RSI, such that (RSI)(MI) is greater than about 26 when is about 0.7; and a Crystallizable Chain Length Distribution Index, LW/Ln, less than about 3.
a Polydispersity Index of at least about 3.0;
a melt index, MI, and a Relaxation Spectrum Index, RSI, such that (RSI)(MI) is greater than about 26 when is about 0.7; and a Crystallizable Chain Length Distribution Index, LW/Ln, less than about 3.
2. The ethylene polymer of claim 1, wherein the Polydispersity Index is at least about 4Ø
3. The ethylene polymer of claim 1, wherein Lw/Ln is less than about 2.
4. The ethylene polymer of claim 1, further having a DSC
Homogeneity Index, DSC-HI, of at least about 7.
Homogeneity Index, DSC-HI, of at least about 7.
5. The ethylene polymer of claim 4 having a DSC-HI of at least about 9.
6. The ethylene polymer of claim 1, further having at least about 0.3 long chain branches per 1000 main chain carbon atoms.
7. The ethylene polymer of claim 1, further having a Crystallizable Rate Constant, CRC, equal to or greater than 1.
8. The ethylene polymer of claim 1 containing about 1 to about 40 percent by weight of a linear or branched alpha-olefin having from 3 to about 20 carbon atoms.
9. The ethylene polymer of claim 1 containing about 1 to about 40 percent by weight of a comonomer selected from propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene and mixtures thereof.
10. The ethylene polymer of claim 1 containing about 1 to about 40 percent by weight of a comonomer selected from propylene, linear or branched alpha-olefins having from 4 to about 20 carbon atoms, and linear, branched or cyclic hydrocarbon dienes, and mixtures thereof.
11. The ethylene polymer of claim 1, wherein said ethylene polymer is a homopolymer.
12. Film comprising the ethylene polymer of claim 1.
13. Clarity film comprising the ethylene polymer of claim 1.
14. Shrink film comprising the ethylene polymer of claim 1.
15. Extrusion coated layer comprising the ethylene polymer of claim 1 on substrate.
16. Wire and cable insulation and/or jacketing comprising the ethylene polymer of claim 1.
17. Crosslinked, power cable insulation comprising the ethylene polymer of claim 1.
18. Molded article comprising the ethylene polymer of claim 1.
19. Insulating jackets and/or semi-conductive jackets and/or shields comprising the ethylene polymer of claim 1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US44245395A | 1995-05-16 | 1995-05-16 | |
| US08/442,453 | 1995-05-16 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2176767A1 CA2176767A1 (en) | 1996-11-17 |
| CA2176767C true CA2176767C (en) | 2001-01-02 |
Family
ID=23756840
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002176767A Expired - Fee Related CA2176767C (en) | 1995-05-16 | 1996-05-16 | Ethylene polymers having enhanced processability |
Country Status (26)
| Country | Link |
|---|---|
| US (1) | US5798427A (en) |
| EP (1) | EP0743327B1 (en) |
| JP (1) | JP3073929B2 (en) |
| KR (1) | KR100267629B1 (en) |
| CN (1) | CN1141306A (en) |
| AR (1) | AR001953A1 (en) |
| AT (1) | ATE200497T1 (en) |
| AU (1) | AU713324B2 (en) |
| BR (1) | BR9602284A (en) |
| CA (1) | CA2176767C (en) |
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