CA2134026C - Tapered block copolymers of monovinylarenes and conjugated dienes - Google Patents

Abstract

A method for preparing tapered block copolymers which are particularly useful for blend components in blends with polymers of styrene. In the first embodiment of this invention the copolymers are prepared in a polymerization process by sequentially charging: (1) an initiator and monovinylaromatic monomers in the presence of a randomizer; (2) an initiator and monovinylaromatic monomers; (3) a mixture of monovinylaromatic and conjugated diene monomers; and (4) a coupling agent; to produce a polymodal tapered block copolymer. In a second embodiment of the invention tapered block copolymers are prepared in a polymerization process by sequentially charging: (1) an initiator and monovinylaromatic monomers in the presence of a randomizer; (2) an initiator and monovinylaromatic monomers; (3) a mixture of monovinylaromatic and conjugated diene monomers; (4) a mixture of monovinylaromatic and conjugated diene monomers; and (5) a coupling agent; to produce a polymodal tapered block copolymer. The invention copolymers and blends of the invention copolymers with polymers of styrene are particularly useful for applications such as packaging and food or drink containers which require transparency, low blueness, colorlessness, good impact strength and ductility.

Description

2 1 3 ~1 ~ 2 ~ 33159C~ ~ ~

TAPERED ~LOCK COPOLYNERS OF ll~.,JVl~l.A~F.~FC
AND CONJUGATED DIENES ~ -Fleld of the Inventlon This lnvention relates to tapered block copolymers of monovlnylarenes and con3ugated dlenes and methods of preparation of these tapered block copolymers.

P~ rc ' of the Inventlon -There hss developed in the polymer fleld, and especlally in the par~Ag~ng and related industries, a need for thermoplastic polymers that can be formed lnto colorless, trflnsparent articles having good impact strength and ductility. There are needs for polymers which are useful as single c- _n~s as well as for use in blends with other commonly used polymers to make artlcles wlth lmproved propertles. The polymers sstisfying these needs should be suitable for use with ~
conventional extrusion, in3ection and blow moldlng equipment and ~lso ~ -suitable for use in other methods of forming plastics into containers, tubes, films, fibers, and the like. Poly~yrene, high impact pol~y~ele, branched block copolymers, and the like have been developed to meet these criteria with various degrees of satisfaction. ;~

~ ' ' .

2 1 ~ J~ ~S ~ ~ 33159CA
~,; 2 Much effort has been dlrected to the preparation of substantially transparent block copolymer resins with a variety of block structures produced by a variety of monomer addition sequences and a variety of coupling agents. Desirable properties and an economic advsntage can be obtained by blending some monovinylaromatic-conjugated diene copolymers with polystryene polymers. However, bec~use blueness of blends of monovinylaromatic-con~ugated diene copolymers with polystyrene polymers c~nnot be predicted by rule of mlxtures behaviors, getting a desirable combination of properties can be a complicated task.
Sometimes relatlvely colorless monovinylaromatic-conjugated diene copolymers give blends with high blueness when blended with colorless general purpose polystyrene.
Blueness of articles formed from various copoly~ers snd blends of copolymers with other polymers ls a longstanding problem in appllcstlons where colorless materials which also have good impact strength and ductlllty are deslrable. Speclflc examples include materlals for water and food contalners.

S~ of th~ Inventlon It 19 an obJect of this lnventlon to provlde novel reslnous tapered block copolymers of vinyl-substltuted aromatlc hydrocarbons and con~ugated dienes from which can be made articles with low blueness and acceptable impact strength and ductllity.
It is another ob~ect of thls lnventlon to provlde novel resinous tapered block copolymers of vinyl-substltuted aromatlc hydrocarbons and con~ugated dlenes suitsble for use ln blends wlth polymers of styrene, p8rtlcularly blends from whlch can be m8de 8rtlcles 2 1 ~
f-~ 33159CA

that exhlblt low blueness and acceptable impact strength and/or ductility. Further, it is an ob~ect to provide novel resinous tapered block copolymers of vinyl-substituted aromatic hydrocarbons and con~ugated dienes which can be used in smaller amounts thPn some of the other commonly used resinous polymodal monovinyl substituted aromatic-conjugated diene block copolymers in blends with polymers of styrene to achieve simllarly low blueness levels and good lmpact strength and/or ductlllty in artlcles made from the blends.
A further object of this invention is to provide novel processes for making resinous tapered block monovinylaromatic/conjugated dlene copolymers, including copolymers suitable for use in blends.
In a flrst embodiment of the invention, copolymers are prepared under solution polymerization condition~ in a reaction zone by~
(a) charging a monovinylsromatic monomer and an initiator in the presence of a randomlzer and allowlng polymerization to occur untll essentially no free r-: -r ls present; thereafter (b) chPrg~ng an initiator and a monovinylaromstic monomer and allowlng polymerlzation to occur untll essentlslly no free monomer is present; thereafter (c) ~h~rg~ng a mlxture of monovinylaromatlc monomer and ~-conJugated diene men~mer and allowing polymerization to occur until essentially no free m~n er is present; and thereafter (d) charging the reaction mlxture with a coupling agent.
In a second embodiment of the inventlon, copolymers are prepsred ln the same manner as those of the flrst embodlment, except th~t additionally, after step (c) and preceeding step (d), a second -sepsrste charge of a mixture of monovinylaromstlc monomer and con~ugsted ,-~ 213 il ~ 2 ~i 33159CA

diene monomer is made and allowed to polymerize until essentislly no free monomer is present before charging the reaction mixture with a coupllng agent.

Detalled De~criptlon of the Inventlon We hflve discovered novel monovinylaromatic/conjugated diene tapered block copolymers which can be used neat or blended with polymers of styrene to produce reslns which can be formed into articles with low blueness and sdvantageous impact properties andlor ductility.
The polymers of this invention are characterized as resinous non-rubbery block copolymers of at least one con~ugated diene with at least one monovinylarene, having at least one random-tapered block and are prepared so that, when the choice of coupling agent permlts, at least a portlon of the flnal product l~ of a brd -~ed, coupled character.
The polymer~ prepared accordlng to thls invention contain from about 55 to about 95, preferably from about 60 to about 90, more preferably from about 65 to about 85, welght percent of copolymerized monovinyl aromatlc monomer based on the weight of total monomer~
employed. Colre~pv..dingly, the lnventlve copolymers contaln from about 45 to about 5, preferably from about 40 to about 10, and more preferably from about 35 to about 15 weight percent copolymerized con3ugated diene monomer based on the total weight of monomers in the copolymer.
The coupled portions of the resinous polymodal block ~-~
copoly~ers of this lnvention have termlnal polymonovlnyl~rene block~ on the ~t~ '~m5 arms of each linear or radial copolymer molecule, and further contain at least one lnternal tapered block of monovinylarene .

p ~ :t - . ~ A ', 2 t 3 ~ 0 2 ~ 33159CA

and conjugated diene. The resinous copolymeric polymodal products also contain portlons of linear uncoupled block copolymers of polytmonovinylarene)-poly(con~ugated dlene); the linear uncoupled block copolymer content is considered to be an important portion of the reslnous product with respect to its overall properties.

C. ~ ts The process of this invention can be carried out using as an initiator any of the organemonoAlkali metal c~ .ds of the formula RM
wherein a ls an alkyl, cycloslkyl or arylcarbanion cont~ining 4 to 8 carbon atoms and M is an alkyl metal cation. Mixtures of organoalkali -~ '~
metal ~ r,~vunds can be used. The presently preferred initiators are ~- ~
alkylmonollthium c . ~c, especially n-butyllithium or - ~ ' sec-butyllithium.
The con~ugatet diene monomers which can be used contein 4 to 6 carbon atoms and include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene and -mixtures thereof. Esch of the charges containing con~ugated diene in the ssme se~L--~e of charges may be the same, but is not necessarily the same, con~ugated diene monomer or ~lxture of conjugated diene m ..~lS.
The presently preferred con~ugated diene monomer is 1,3-butsdiene.
The monovinylaromatic monomer~ which can be used contain 8 to 12 carbon atoms and include styrene, alpha-methylstyrene, 4-methylstyrene, 3-methylstyrene, 2-methylstyrene, 4-ethyl~tyrene, 3-ethylstyrene, 2-ethylstyrene, 4-tert-butylstyrene, 2,4-dimethylstyrene and ~ ' ~ed aromatic~ such as vinyl nspthalene and mixtures thereof.
Each of the charges containing monovinyl~romatic monomer in the same , . , , ~ . .. , . ., ., . .. . . . . .. . .. . . , , . . ~ .. . ~ ..... . .. .. .... . . . . . . . . . .
... ... .. .. .

3 ~ fi sequence of charges may be the same, but ls not necessarily the same, monovlnylaromatic monomer or mixture of monovlnylaromatic monomers. The presently preferred monovlnylaromatlc monomer ls styrene. -Examples of polar ~ r.und~ whlch can be Qdvantageously employed as randomlzers are ethers, thloethers tsulfldes) and tertiary amlnes. It ls usually preferred to use ethers and sulfldes ln whlch the radicals attached to the oxygen or sulfur atoms are hydrocarbon radlcals. Specific examples of such polar materlals include dlmethyl ether, diethyl ether, ethyl methyl ether, ethyl propyl ether, di-n-propyl ether, di-n-octyl eth0r, anisole, dloxane, 1,2-dimethoxyethane, dibenzyl ether, dlphenyl ether, 1,2-dimethoxybenzene, tetramethylene oxide (tetrahydrofuran), dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, di-n-butyl sulfide, methyl ethyl sulfide, dimethylethylQmine, trl-n-ethylamine, tri-n pr~Jlamine, tri-n-butylamine, trimethylamine, triethylQmine, tetramethylethylenediamine, tetraethylethylelled~r~~ne, N,N-di-methylaniline, N-methyl-N-ethylaniline, N-methylmorpholine, and the like. It is to be understood Qlso that mlxtures of these polar ~ '~ can be employed in the practice of the present invention. The polar c~m, 'c are generally used in admixture with the hydrocarbon diluent. Presently preferred are either tetrahydrofuran or diethyl ether.
Among the ~uitable coupling agents are the di- or multivinylaromQtic & A .u..ds, di- or multiepoxides, di- or multiisocyanQtes, di- or multilmines, di- or multialdehydes, dl- or multiketones, alkoxytin ~ m,~ '-, di- or multihalide~, particulQrly ~ilicon halides and hQlosilQnes, mono-, di-, or multiQnhydrides, mono-, 21~A~2~
~' 33159CA

di-, or multiesters, preferably the esters of monoalcohols with polycarboxylic acids, diesters which are esters of monohydric alcohols with dicarboxylic scids, lactones, monobasic acids with polyalcohols , ~ ,~.".:
such as glycerol, and the like, includlng c~"eu-lds containing two or ~ ~ ~ r more groups and mixtures of two or more compounds. -Examples of suitable vinylaromatic coupling agents include, -~
but are not limited to, divlnylbenzene, 1,2,4-trivinylbenzene, ;
1,3-divinylnaphthalene, 1,3,5-trivlnylnaphthslene, 2,4-divinylbiphenyl, -~
p-diisopropenylbenzene, and the like. Of these, the divinylaromatic hydrocarbons are preferred, partlcularly divinylbenzene in either its ortho, meta, or para isomer. Commerclal divinylbenzene which is a mlxture of the three isomers and other c m"ou.,ds is satisfactory. ~-: . .
Ep~Yi~l7sd hydrocarbon polymers such as epox~7s~ liquid ~-polybutadlene and epoxy ~ such as 1,2; 5,6; 9,10-triepoxydecane, and the llke, can be used as coupling agents.
Organoalkyl phosphites and arylalkyl phosphite~ are consldered useful as coupling agents in this invention.
Examples of suitable multilsocyanate coupling agents include ben~~~~ 1,2,4-triisocyanate, naphthalene-1,2,5,7-tetraisocyanate, and the like. Commercially avallable products known as PAPI-l, a polyarylpolyisocyanate having an average of 3 isocysnate groups per molecule and sn average molecular weight of about 380 are suitable.
The multlimines, also known as multiaziridinyl ~ e~ such as those contsining 3 or more azlrldlne rlngs per molecule, are useful as coupling agents. Other cD.:pu_nds useful as coupling agents lnclude tetravinyl sllane, trivinyl phosphine, the triaziridinyl phosphine oxides or sulfides such as tri(l-aziridinyl)phosphlne oxide, ~i ~ A~~ .. t '~ .'-k'i~ ,~ '~ """, , ? ''~ .r ,. ~ j -~213 ~ ~ 2 ~ 33159CA

tri(2-methyl-1-aziridlnyl)phosphlne oxide, tri(2-ethyl-3-decyl-1-a~iridinyl)phosphine sulfide, and the like.
The multialdehyde coupling agents are represented by c-ml,~ul-ds ;
such 8S 1,4,7-naphthalenetricarboxyaldehyde~ ;
1,7,9-anthracenetricarboxyaldehyde, 1,3,5-pentanetricarboxyaldehyde, and similar multialdehyde-containing allphatic and aromatic c-m~.u.,ds. The multiketones are represented by c. ..u..ds such as 1,4,9,10-anthracenetetrone, 2,3-diacetonylcyclohexanone, and the like.
Examples of the multianhydrides include pyromellitic dianhydride, styrene-maleic anhydride copolymers, and the like. Examples of the multiesters include diethyladipate, triethylcitrate, 1,3,5-benzenetrlcarboxylic acid, trlethyl ester, and the like.
Among the multihalide coupllng agents are the sillcon tetrahalldes such as slllcon tetrachlorlde, slllcon tetrabromide, and sillcon tetralodide; the trihalosilanes such as trichlorosilane, trlchloroethylsllane, trlbr~ ~cnzylsllane, and the llke; and the multlhalogen-sub~tltuted hydrocarbons, such as 1,3,5-trl(bromomethyl)benzene, 2,5,6,9-tetrachloro-3,7-decAdl~ne, and the llke, ln whlch the halogen is attached to a carbon atom which is alpha to an actlvatlng group such as an ether llnkage, a carbonyl group, or a carbon-to-carbon double bond. Substltuents lnert wlth respect to lithium atoms in the terminally reactlve polymer can also be present ln the actlve halogen-containing c ~_ ~c. Alternatively, other sultable reactlve groups dlfferent from the halogens as described above can be pre~ient.
Other metal multlhalides, partlcularly those of tln, lead, or germanium, can be employed as coupling and branchlng agents. Slllcon or :~' ' ' i ;, ' ; '.;. ," ~

2~3 ~a2~ 3315~CA

other metal multialkoxides, such as slllcon tetraethoxlde, are also sultable coupllng agents. ~ -~
Examples of compounds contslning more than one type of ~ -functionsl group include 1,3-dichloro-2-propanone, '~
2,2-dibromo-3-decanone, 2,4-dibromo-3-pentanone, 1,2; 4,5-diepoxy-3-pentanone, 1,2; 4,5-diepoxy-3-hexanone, 1,2; 11,12-diepoxy-8-pentadecanone, 1,3; 18,19-diepoxy-7,14-eicosflnedione, and the like. ;
Useful multifunctional coupling agents include epoxidized vegetable oils such as epoxidized soybean oil, epoxidi7ed linseed oil ;- ;
and tbe like or mixtures thereof.
The presently preferred coupling agent is epoxidized vegetable oll. Presently preferred is epoxidized soybean oll.

Proce~s The un~que polymodal tapered block ch~racter of the polymer ant low blueness and good lmpact strength and/or ductility of articles made from the polymer or blends of the polymer of the fir~t .~ r of thls inventlon are protuced by the unlque sequences of two sep~rate initial charges of monovinylaromatic monomer and initiator, followet by a separate charge of a mixture of monovinylaromatic monomer snd conJugated diene, and a subsequent coupling step.
The unlque polymodal tapered block char~cter of the polymer and low blueness and good impact strength and/or ductility of articles made fro~ the polymer or blends of the polymer of the second of this invention are produced by the proces~ of the fir~t embotiment with the additlon of a second separate charge of a mlxture of monovinyl 213;i.~2~ 33159CA
.~, ,,;,............................................................ .

aromatlc and conjugated diene monomers next preceeding the coupling step.
In each of the two embodlments of this invention the first initiator charge produces active livlng monovlnyl aromatic component polymer block~ with alkali metal atoms (from the initiator) on at least one end to form active reaction sites. Each subsequent monomer charge adds monomer to the llving polymer chain at the alkali metal reaction site. At each stage of charging, polymerization is allowed to continue until essentially no free monomer is present.
With each subsequent charge which includes initiator a new polymer-alkali metal species will be produced, and each subsequent monomer charge has ~n opportunity for polymerlzation of part of the charge with each of the exlsting polymer-alkali metal specles. Each of the actlve living polymer chains will have terminal monovinyl ~romatic blocks on both ends after polymerizatlon of each monomer charge contalnlng monovlnyl aromatlc. EveD when mixtures of monovlnyl aromatic monomer and conJugated dlene are charged, the polymer chalns wlll have termlnal monovlnyl aromatic blocks on both ends. After vlrtually complete poly~erization of the final monomer charge, the active living linear block copolymers are charged wlth a difunctional or polyfunctlonal coupling agent to allow coupllng of each of the living specles wlth each of the other living species or with others of the same living specie~ to form the desired polymodal tapered block copolymers.
If the coupling agent is not lO0 percent efflclent and/or lf less or more than a stoichiometric amount of coupling agent is used, there can ~ ;
be some uncoupled terminated polymer chains of each of the species in ~
the final re~ction mixture. ~ ~-'' . - '' ~
~ ", 2l3 ~.a2~
33159C~

Use of dlfunctional coupllng agents will produce predominantly linear polymer chalns. ~epending upon functionfllity, v~rious degrees and kinds of branching may be accomplished with polyfunctional coupling agents. VarLations in the amount of fl partlcular polyfunctional coupling agent also can be usad to manipulate the degree and kind of branching at the coupling sltes.
The charging sequences of this invention and the resulting polymers at each stage are exemplified using a selected monovinylaromatic monomer, conjugated diene and polyfunctional coupling agent in the following Tables 1 and 2.

~ ~;..~

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TABL~ 1 Invention CharginR Sequence (First Embodiment~
ChargeContents of Charge Resulting Polymer Chains (a) randomizer, inltiatorlSl-Lil -and styrene (b) lnitiator2 and styrene2Sl-S2-Lil S2 -Li2 (c) butadiene~ and styrene3Sl-S2-B~/S3-Lil S2-Bl/S3-Li2 (d) coupling agent polymodal t~pered block ~:
copolymers with styrene terminal blocks : :

where S = styrene B = butsdiene B/S = tapered block Li = resldue from a monoalkali metal initlator remaining on the end of the polymerization chain or reaction site prior to termination or coupling.
subscripts = designation of the numerical order in which -~
that particular c ., ,ent was charged or ~:
formed.

, ~, 9 2 ~ ~
-~ 33159CA

Invention CharRln~ Sequence (Second Embodiment) -~;

Charge ~ontents of ChargeResulting Polymer Chains (a) randomlzer, initiatorlSl-Li~
and styrene~

(b) lnitiator2 flnd styrene2 Sl-S2-Li~

(c) butadiene~ and styrene3Sl-S2-B~/Sl-Li~
S2-B,/S3-(d) butadiene2 and styrene~S~-S2-Bl/S3-B2/S~-Li S2-B,/S~-B2/S4-Li2 (e) coupllng agent polymodal block copolymers wlth styrene termlnal blocks where S = styrene B = butadiene B/S = tapered block :
.. . .
Li = resldue from a monoslkali metal initiator ~~--~n~ng on the end of the polymerization chain or re8ctlon slte prior to termination or coupllng. ~
... ~.
subscrlpts = designatlon of the numerlcal order ln which that partlcul8r c~ . _nt wss charged or ~ -formed.
The r8ndomizer ls usually 8dded with the diluent initially ' charged to the reactor. Each of the charges which hss two - ner~ m8y be either a mlxture of the two m me ~ or ~lmultaneous ~hn~g~ng of two separate - ~ s.

~ ~ 1 3 ~ ~ 2 ~ 33159C~
, ~ "

As can be seen from the lntermedlflte products listed in the charging sequence tables above, in two embodiments of the invention -~
there are at least two distinct species of polymer chalns before coupling. Thus, polymodsl tapered block copolymers comprising relatively hlgh and low molecular weight species can be produced.
Tapered blocks in each of the growing polymer chains are produced by ~imultaneously charglng with at leflst two monomers as shown in the preceedlng tables of the inventive charging sequences.
The randomizer regulates tapering or random polymerization of the monovinylaromatic monomer and the con3ugated diene in a mixed monomer charge. Choice of randomizer can be used to manipulate the degree and direction of taper in blocks resulting from charges of mixtures of monomers. The taper can be elther a graduation from con3ugated diene rich chain to monovinylaromatic rich chain or a -graduation from a monovinylaromatlc rich chain to con3ugated dlene rich -chain accordlng to preference of the lnltlator-randomizer complex for one tgpe monomer over the other. For example, when tetrahydrofuran ls used as a racl ~7~r~ the dlene enters lnto the chaln faster than the monovlnyl substltuted aromatic; therefore, when both the monovlnylaromatlc monomer and the con3ugated dlene are present, the block tapers gradually from an essentlally polybutadlene block to an essentially monovlnyl substltuted aromatic polymer block.
The welght ratlo of monovlnyl substituted aromatlc monomer to con3ugated diene monomer ln each of the tapered blocks i6 from about ~-1:0.63 to about 1:2, preferably from about 1:0.67 to about 1:1.8, and - ~
more preferably from about 1:0.8 to about l:l.S. The weight ratios of ~ ' monovinyl substituted aromatic n ~m~r to con3ugated diene monomer ln ~

~,'.';''~
': ,:' "' 213 ~ ~ ~ 6 33159CA
; 15 each of the tapered blocks in the same polymer cha~n do not have to be the same. See Example VII.
Generally each of the two tapered blocks made in steps (c) and (d) of the second embodiment of thls invention can be of equal size;
however, flctual sizes of the two tapered blocks can vary within the same ~-copolymer depending upon the amounts of monomers charged ln each of thr third and fourth monomer charges. See run 13 ln Example VII. ~
Prior to coupling, all of the living polymer chains have ~6 monovlnylaromatic terminal blocks on one end because of the initlal monovinylaromatic charge (a) and charge (b) made with initiator; the living ends of the chains will have tapered blocks prior to coupling , " ~.,~,,.
because of the charge containing both monovinylaromatlc and conJugated diene monomers made next preceedlng the coupllng step.
In uddltlon to the sequence of addltlons of the monomers and of the lnltlator, lt ls lmportant to control the amount of each monomer and inltiator addition at each stage or increment so that a suitable proportion of block sizes and proportlon of polymodality is obtained. ;~
Generally in a presently preferred first embodiment of this invention, if a polymer which is about 75 weight percent monovinylaromatlc, based on total monomer weight, ls used, from about 27 ;~
to about 80 weight percent of the total monovinylaromatic monomer ls charged in step (a), from about 5 to about 21 weight percent of the total monovinylaromatic monomer is charged in step (b), and from about 7 to about 60 welght percent of the total monovlnylaromatic monomer is charget ln step (c). Generally more preferably, from about 40 to about 67 woight percent of the total monovinylaromatic monomer is charget in step (a), from about 8 to about 19 welght percent of the total ~3~2~ 33159C~

monovinylaromatic monomer i9 charged in step (b), and from about 27 to about 40 weight percent of the total monovlnyl~romatlc monomer is charged in step (c). Generally presently most preferflbly, from about 47 to about 60 welght percent o~ the total monovinylaromatic monomer is charged ln step (a), from about 11 to about 16 weight percent of the total monovinylaromatic monomer is charged in step (b), and from about 29 to about 37 weight percent of the total monovinylaromatic monomer is charged in step (c).
Generally in a presently preferred second embodiment of this invention, if a polymer which is about 75 weight percent monovlnylaromatic, based on total monomer welght, is used, from about 27 ,. ~
to about 80 welght percent of the total monovinylaromatic monomer is charged ln step (a), from about 5 to about 21 weight percent of the .
total monovinylaromatic monomer ls charged ln step (b), from about 3 to about 19 welght percent of the total monovlnylaromatlc monomer is ~..... ... .;
charged ln step (c), and from about 13 to about 36 welght percent of the .
total monovlnylaromstlc monomer ls charged ln step (d). Generally more preferably, from about 40 to about 67 weight percent of the total ~ ~
monovinylaromatlc monomer is charged in step (a), from about 8 to about ~.:
19 welght percent of the total monovlnylaromatlc monomer i8 charged in . . .
step (b), from about 5 to about 16 weight percent of the total ; -~
monovinylaromatic monomer is charged in step (c), and from about 16 to .~.s'~
about 32 weight.percent of the total monovlnylaromatlc monomer ls ~:~
charged in step (d). Generally presently most preferably, from about 47 to about 60 weight percent of the total monovinylaromatic monomer is -~
charged in step (a), from about 11 to about 16 weight percent of the total ~onovinylaromatic monomer i8 charged in step (b), from about 8 to ~ ' ~

213~9~ 33159CA ~-lt about 13 weight percent of the total monovinylaromatic monomer i9 charged ln step (c), and from about 20 to about 25 weight percent of the total monovlnylaromatlc monomer is charged in step (d).
In elther of the two embodlments of this invention it ls feasible to stretch out over an interval of time the flddition of one or more of the lncrements of initiator, thus spreading (increasing) further the polymodality of the resulting product upon coupl~ng.
The polymerlzation proce~s is carried out in a hydrocarbon ~-~
dlluent at any suitable temperature in a range of about -10~ to about 150~C, prefer~bly in the range of about 0~ to about 110~C, at pressurss -~
sufficient to maintaln the reactlon mlxture substantially in the llquld phase. T~m~aLa~res and pressures wlll peak during polymerization of ~-each monomer charge and then decrease when essentially no free monomer is left to react. Appropriate hydroc~rbon dlluents include linear and cycloparaffins such as butane, pentane, hexane, octane, cycl~h ~ ~
cyclopentane and mixtures thereof. Presently preferred is cyclohexane.
Generally the cholce of hydrocarbon or hydrocarbon mixture and the t~m~ar6~re is such that the resultlng polymer is in solutlon.
Small a-ounts of polar s . '~ are used to lmprove the effectlveness of fllkylmonoalkali metal inltlators such as n-butylllthlum; dlssoclatlon of the alkylmonoalkali metal lnltlators affects the rate of lnltiatlon and polymerlzatlon. The polar c~ . . 's also effect partlal ~ tlon of the vlnylarene/con~ugated dlene so as to lncrease the random portion of the tapered block. The polar m, _ ~c are generally used in admlxture wlth the hydloca-L - dlluent.
The amounts of polar ~ used as ra~d~ ~7~rs and promoters of effectivenes~ of lnitlfltors ln thls lnventlon wlll vary 213~0~

accordlng to the reactlvlty and effectlveness of the particular randomlzer used. For example, 1,2-dimethoxyethane, tetramethylethylenediamine and 1,2-dimethoxybenzene are much more efficlent randomlzers than most of the others llsted above when used wlth the partlcular lnltiators and monomers used in the lnvention runs described below. However, tetrahydrofuran is often used because the ~
reactlon wlll go nearer to completlon ln a shorter tlme after the ~ -lnitial reactlon ln the monomer rich environment. Also, there are dramatic variations in the amounts of each of these most efficient ~ ~
randomizers whlch will be needed. For example, for polymeri~ations such ~ ~ ;
as those shown in the examples of invention runs in Example I of this application, much less tetrahydrofuran than 1,2-dimethoxyetnane would be ~ '~
needed. -The amounts of polar ~ ~u..ds used as randomizers will also vary according to the desired molecular structure of the portions of tapered blocks which result from con~ugated dlene addition. For ;' example, when using tetrahydrofuran, and it is desirable that the tapered blocks of the polymer have nearly equal amounts of 1,4 addition of butadiene and 1,2 addition of butadlene or only a little more 1,4 addltion than 1,2 addltion of butadiene, larger amounts of the tetrahydrofuran would be used than when more 1,4 addition i8 desired.
When polymers with higher vinyl character resulting from 1,2 addition in excess of 1,4 addition are desired, then the useful amounts of tetrahydrofuran needed would be considerably larger. However, use of too much rRnd: 1~er can result in excessive polymer-lithium termlnation durlng polymerization and/or poor stability of the polymer and/or undesired side reactions, depending upon choice of rAn~ 7er. Use of 213'~2~1 too little randomizer would result in inefficient initifltor use, compositlonal variations and broader molecular weight distribution.
The initial monovinylaromatic charge is made with the randomizer present for the additionfll effect of causing the monovinylaromatic component resulting from each inltifltor charge to be of relatively narrow moleculflr weight distribution. In the two embodiments of this invention, by varying the amounts of initiator in each of the two charges having initiator, the differences in molecular weights of the monovinylaromatic components resulting from each of the ~
two chsrges can be increased. ~'<
In each of the two embodiments of the invention, amounts of initiator employed are those which will produce resins with desirable melt flow which can be used in blends to make articles with a good balance of properties including minimal blueness, and good impact strength and/or ductility. Presently preferred when making invention polymers to be used in blends are amounts of initiator in each of the two lnitlator charges sufficient to obtain a block copolymer having a melt flow in the range from about 2 to about 50 g/10 minutes, more preferably from about 4 to about 30 g/10 mlnutes, and most preferably from about 7 to about 20 g/10 minutes, as determined by ASTM D1238-73, conditlon 200~C/5.0 kg. The amounts of lnltlator contemplated as useful in each of the two charges having lnitiator are shown in Tables 3 and 4.
Use of too small an amount of initiator would result in high molecular welght polymers. Conversely, use of too large an amount of initiator would result ln polymers havlng short chaln polymeric species and low molecular weight.

r~~ 213~2~ 33159CA

The weight rutio of the amounts of initiator in each of the charges having initiator can be represented as 1:0.25-300.

,~''. ,'' '. ' Lll : Li2 :: l : 0.25-300 wherein Lil = initiator in the first charge Li2 = initiator in the second charge More preferably for most applications, the amount of initiator in the second charge of initiator is from about 0.3 to about 10 times, bssed on weight, a~ much as the amount of initiator in the first lnltlator charge. Generally, presently most preferably, the amounts of ;~ -lnltlators are selected such that the amount in the second charge is only slightly smaller, equal to, or larger than that employed in the first charge.
Varylng the weight ratlos of amounts of the initlator charges wlll result ln varlatlons of the proportionate amounts of species present ln the copolymer. Other factors affecting the proportionate -~
flmounts of species present in the copolymer include presence of lmpurities and/or scavengers in the reac*or, effectlveness of the polar d~ ~P~r as a promoter and choice of coupling agent(s).
The polymerlzatlon is carried out in a substantial absence of ~ ;
oxygen ant water, preferably under an inert gas at ~sphcre. Prior to -~
the coupling step, the reaction mass contains a very high percentage of molecules (polymer chsins) in which an alkali metal cation ls posltloned at one end of each polymer chain. Impurities in the feed such as water or alcohol reduce the a~ounts of monoalkali metal polymer ln the reaction mass.

213 ~ Q 2 ~ 33159CA

After essentifllly complete polymerization of the final charge added to the polymer, one or more suitable dlfunctional or polyfunctional coupling agents is added. As used here, the term "coupling" means the bringing together and ~oining, by means of one or more central coupling atoms or coupling moieties, two or more of the living monoalkali metal-terminated polymer chains. A wide variety of c ~ ds for such purposes cfln be employed.
Any effective amount of the couplin~ agent can be employed.
While the amount is not believed to be particularly critical, a stoichiometric amount relative to the active polymer-slkali metal tends to promote ~Y~ coupllng as a generality. Presently preferred is an amount of coupling agent slightly grester than stoichiometric relative to the actlve polymer-alkali metal. However, less than stoichiometric amounts can be used for higher degree~ of coupling where desired for partlcular products of broadened moleculflr weight distribution.
Typicslly, in each of the a~'~'~~ Ls of th$s invention, the total amount of coupling agent is in the range of sbout 0.005 to 10 phm (parts per 100 parts of total m~ ~ employed in the polymerization).
Preferred when most combinations of monomers 8nd coupllng agents sre used to practice this lnvention 18 about 0.2 to about 0.6 phm of coupllng agent, dep~n~ng on amounts of initiator used. Presently most preferred is about 0.3 to about 0.5 phm, depf-'lng upon amounts of initiator used. Use of an amount of A reasonably highly efficient coupling agent within these ranges provides polymers with a moderately broad moleculflr weight dlstributlon that h8s proven useful to custom molders. Use of an insufficient amount of coupling agent will result in less complete coupling of the livlng polymer chains or, depan~lng upon ' ' . '~.

'd . ~ ' ~,~ , ",~

~ r; " , ,, ~ .s ~ 'Yi ~ s ~ 213 ~ ~ 2 ~ 33159CA

cholce of coupling agent, more branchlng; use of an excessive amount of coupling e8ent wlll also result in more uncoupled chalns.
At the conclusion of the coupling process, the coupled polymer ;
may still contain bound polymeric alkali metal alkoxides depending on the type of coupling agent employed. The system is treated with an active c ..c ~ such as water, alcohol, phenols, carbon dioxide or linear saturated aliphatic mono- and dicarboxylic acids to remove any r~ n~ng alkali metal from the copolymer chain.
While the polymer product i~ still in solution, stabilization agents can be added. Additional stabillzers could be added during finishing before pelletizing. This treatment will provide oxidative ~ ~
stability for the polymer during processing and handling and subsequent ~ -;
long term use by the customer.
Commonly used stabilization processes can use a combination of c~, ~c whlch include, but are not limited to, a hindered phenol ~nd an ~a~ hGDphite, particular examples of which are octadecyl 3-(3',5'-dl-t-butyl-4'-hydloA~he..yl) propionate and tris-nonylphenylphosphite.
After stabllization, the hydrocarbon diluent is then flashed from the polymer solution to increase the solids content. The polymer -cement, i.e., the polymer in the polymerlzation solvent, usually contains about 10 to 40, more usually 20 to 35, weight percent solids, the balance solvent. Preferably, but not necessarlly, the polymer cement ls flashed to remove by evaporAtion a portion of the solvent so as to reduce the solvent content to a concentration of about 0 to 50, more usually about 0 to 10, weight percent (co.-esp~-lding to a solids -213 ~ ~ 2 ~ 33159CA
~~............................................... 23 '~ :

content of about 100 to S0, more usually about 100 to 90, welght percent).
Flashing of the polymer cement may be followed by desolventizlng extrusion wlth vacuum in commerclal production or by other vacuumlng processes to flchieve consistent solvent content of less than 0.3 welght percent.
The resinous copolymeric products c~n be, and normfllly are, C_, Jl ~ed with anti-oxidants, anti-blocking agents, release agents and other additives, as known in the c~.rsunding arts.
Typical charging sequences and useful ranges of amounts of the charges for each of the two embodiments of this lnvention are given in Tables 3 and 4.

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'J ~' ~ 33159CA
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213~02~ 33159CA
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~ iYt a't ~ a D -Ct ~ ~ ~ 0 ~
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After coupling at leflst the coupled ~nd uncoupled polymeric specles shown in Tables 5 and 6 are present ln the polymod~l polymers of ~ :
the first and second embodlments, respectively, of this invention.

Polymeric Species Included in First Embodiment S,-S2-Bl/S3-X-s3/Bl-s2-s~
Sl-S2-Bl/S3-X-s3/Bl-s2 S2-Bl/S~-x-S3/PJl-s2 S2-Bl/S, ''~

~ ',, S = monovlnylaromatic block - :~
B = conJugated diene block ' B/S = tapered block x = coupliDg moiety or coupllng slte :~
~ubscrlpt~ = lndicatlons of the charges whlch were the ~-source of tbe polymer blocks.
- , ~ -~, . ~, -, -. .
,, .,:
', .
~ ~

,, . " . , .

, ~,:,......
: ~' '-~'''"~
. :.::::

'';-2~ 3 i~2~
,~ 33159CA

TABL~ 6 Polymeric Species Included ln Second Embodlment Sl-S2-BI/Sl-B2/S4-X-S4/B2-S3/BI-S2-S
Sl-s2-Bl/s3-B2/s~,-x-s4/B2-s3/Bl-s2 Sl-S2-BI/S3-B2/s4 S = monovinylaromatlc block B = conjugated diene block B/S = tapered block ~;
x = coupling moiety or coupling site subscripts = indications of the ch~rges which were the source of the polymer blocks.
In each of the embodiments dependlng upon choice snd amount of coupling agent or agents and whether coupllng ~gents are charged as a mlxture or incrementally, there can be present other polymerlc species ~;~
with ~arying degrees of branching.

Blends ; The reslnous polymodal copolymer products of thls invention can be blended with other polymers such as acrylonitrile-butadlene-styrene copolymers (ABS), styrene-acrylonitrile copolymers (SAN), and other styrene copolymers. When less transparency i8 desired or tLa,-~arency is not necessary, the invention copolymers can be blended with polyolefins and/or olefln copolymers.

213'il~2~ ~
~ 33159CA
. . .

~ lends of the invenL~on polymers with polymers of styrene are partlcularly useful applications for the lmproved tapered block copolymers of thls lnvention. Artlcles m~de from these blends have surprlslngly low blueness and advantageous impact strength and/or ductillty. For example, articles made from styrene homopolymer and elther of the two embodlments of this inventlon typically have Hunter -negative b blueness values of less than 20, most often less than 18.
Thus, less of the invention copolymer is needed to achieve high impact strength, while retaining reasonably low blueness, in articles made from blends with styrene homopolymers than would be needed of other comparative polymodal monovinylaromatic-con~ugated diene block copolymers.
The presently preferred polymers of styrene employed in the ~ ~-blends of this invention are usually ~a) homopolymers of styrene; or (b) ;~
copolymers of styrene as a ma~or c~ pvnen~ with a minor amount of any ;~ ~ -other copolymerizable monovinyl sromatic C~ ' other than styrene, such as al~'- methylstyrene, vinyltoluene or para-tertiary-butyl styrene. A minor smount of other monomers such as methyl acrylate, methyl methacrylate, acrylonitrile and the like c~n be copolymerized :
with the styrene.
The invention copolymers can be blended w$th styrene resins made in bulk polymerization. These resins are commonly prepared by heating styrene and any ~cc ~ cmor at temperatures in the range of 100~ -~
to 200~C with applicatlon of pressure, if necess~ry, to combine the ers. The polymerization can also be carried out at lower ti~m~3LaLu~es by the addition of free-radical generating peroxldic catalysts such flS benzoyl peroxide, acetyl peroxide, di-t-butyl peroxide 2~ 3'~0~

;~ 29 and the llke. Alternatively, the polymerlzatlon can be c~rried out ln suspension to yleld a dry powder or in emulsion, usually resulting in a latex of polystyrene which can be coagulated to yield the solld powdery polystyrene. The polymerization can also be carried out ln solution with precipitation of the product, if desired. Solvent can be removed by standard techniques such as steamstripping or solvent avaporation.
High impact polystryene (HIPS) also can be successfully ~~
employed in blends with the invention copolymers. Sult~ble high lmpact polystyrenes can be prepared by polymerizing styrene in the presence of an elastomer, typically polybmtadiene rubber. In these resins the polystyrene forms the bulk of the resin throughout which the grafted rubber polystyrene particles flre dispersed. -~
The blends of this inventlon can be prepared by any suitable means lncludlng blendlng, tumbllng and extruslon. Examples of these methods lnclude, but are not limited to, dry mixing in the form of a powder or pellets, wet mixing in the form of a solution or slurry, and melt extrusion ~ ng.
The polymers and any other ingredients or additives may be me-h~n~lly blended together in the desired proportions wlth the aid of any suitable mlxing device conveniently used for mixing rubbers or plastics, such as, for example, A differentlal roll mill, a ~anbury mixer, or an extruder.
In these types of blending methods the polymers and any other c~ml ~- ts and ~ddltlves used can be in any form, such as, for example, fluff, powder, granulate, pellet, solutlon, slurry, and/or emulslon.
Any additive can be combined with the polymers according to any method known ln the art. Examples of lns~ rorstlon methods lnclude, but are i ' ~ ' r~

~ 1 3 ''I ~ 2 fi 33159CA

not limited to, dry mlxlng tn the form of a powder and wet mixlng in the form of a solution or ~lurry.
Melt extrusion compoundin~ c~n be carried out using any suit~ble method such as in s~ngle screw or twin screw extruders or other melt extruders st temperatures above the melting point or glass trsnsition temper~ture of the polymers.
The presently preferred method compri~es blendlng the polymers ln powder or gr~nulste form and extruding the blend in sheet form to feed a thermoformer or direct feed to an in~ection or blow molder. ;~
In order to facilitate thorough mixing of the polymers and to ~ ~*,;
develop the deslred combin~tion of physical properties, pellets are gener~lly met0red by loss-ln-weight feeders or by screw feeders ~t a ' temperature low enough to avoid softenlng the pellets. The metered ~ ;
pellets are dropped into an extruder which melts and blends the ~-c-m,_:.e ts to provlde a h ~geLJ.~ melt.
Alternatlvely, solutlon blendlng methods known in the art msy be used.
The ranges of amounts of polymers useful in blends varles sccordlng to the properties and economics requlred. For example, when sn invention copolymer iB blended with a polymer of styrene, prsctlcsl r~Dges include using amounts such a8 from sbout 10 to sbout 70 weight percent polymer of styrene, more ususlly from about 20 to about 65 weight percent polymer of styrene, and most preferflbly from about 30 to ~ -about 60 weight percent polymer of styrene with the balance belng one or more of the polymodal resinou~ copolymer p~t~ts of thls invention.
For a more psrtlculsr exsmple, when the inventlon copolymers are blented ;
with genersl purpose polys~yLenc~ brosd rsnges lnclude uslng smounts 21 ~ 2 ~
,-~ 33159 such ~ from ~bout 10 to abollt 70 weight percent polystyrene, more usually from ~bout 20 to About 65 welght percent polystyrene, and most preferably from about 30 to flbout 60 weight percent polystyrene with the balflnce belng one or more o~ the polymodal resinous copolymer products of this lnvention. Generally, use of too much of the invention copolymers ln a blend would reisult ln good properties but loss of economlc advantage. Use of too little of the invention copolymers in a blend would result in loss of impact reslstance. These blends can be economical ways of gaining the desirable attributes of both polystyrene ;~
and the invention polymers while maintaining low blueness in articles made from the blends.
The compositions of thls invention or blends thereof caD be extruded, thermoformed, in~ection molded, blow molded, or made into films or sheets. Articles made from the compositions of this invention are transparent with low blueness, have good impact strength and have other physical properties within acceptable ranges for such applications as drinking cups, lids, bottles, other food containers, medical drainage units, shrink wrap and over-wrap. Articles made from blends of the copolymers of thls invention can economically provide adv~ntageous properties for similar applications.

Test P,.~id e3 The blend blueness values were determined on a Hunter Lab colormeter Model D 25 using the Hunter Lab procedure. Blueness values are expressed as -b, where larger absolute numbers indicate more blueness.

2~ 32~

~: ' ;: 32 Other properties were tested using ASTM procedures as shown in Table 7.

Test Procedures Used Property ASTM Method Flow rate, g/10 min D 1238-88 ~ -Condition 200~C/5.0 kg ~ .
Haze, % D 1003-61 (1990) .
Transmittance, % D 1003-61 (1990) Shore D hardness D 2240-91 Tenslle strength at yield and D 638-91 at 50 mm/min '~
break, MPa Type I test specimens Elongation at yield and break, % D 638-91 at 50 mm/mln Flexural modulus, MPa D 790-86 Izod lmpact strength, D 256-88 ~ .
notched, J/m ~ :
Vlcat softeDlng point, ~C D 1525-91 ~ ~ ' Total energy dart drop, J D 4272-85 ~ h :,~

E~ P1e8 .
The followlng examples will describe in more detall the experimental process used and the polymodal tapered block copolymers wlth vlnylarene termlnal blocks obtalned a8 a result of the process and blends made wlth the invention copolymers. These examples should be taken as illustrative and not restrictlve. :~'~

'' 213 ~ ~ 2 ~ 33159CA

Styrene and butadiene were chosen AS monomers to exempllfy the lnvention, and randomizer, initiator, coupling agent and diluent flppropriate for these monomers were used. Quantities of reagents are usually expressed in parts per hundred monomer (phm) based on the total weight of monovinylarene and con~ugated diene employed.

Example I
This example descr~bes four invention polymerization runs (1, 2, 3, 4) that were carried out to produce resinous polymodal, coupled, tspered block styrene-butadiene copolymers with resinous terminal blocks. These runs exemplify the first embodlment of the invention.
Styrene (from Stlrling Chemical) and 1,3-butadiene (from Texas El Paso) were drled by psssage over actlvated alumlna (Kaiser A-201), and then copolymerized and coupled ln a 4-stage proces~ using n-butyllithium lniti~tor (from Lithium Corporation of Amerlca). ;
Polymerizatlon runs were carried out under nitrogen in a stirred, ~acketed, stainless steel 7.6-liter reactor employing essentlally anhydrous reactants and condltions. The anhydrous mixtures were stlrred continuously during the polymerization process. The cyclohexane diluent, whlch contalned 0.04 phm tetrflhydrofuran (THF) ln each polymerization in this example, wss preheated to about 50~C before r- ~ -r~ were charged to the reactor. The n-butyllithium was charged as a 2 welght percent solutlon ln cyclohexane. In the polymerlzation step in which both butsdiene and styrene were chsrged, they were chsrged simultaneously a8 a mixture.
In the coupllng step, the Vikoflex0 7170 coupling agent used was an epoY~ e~ vegetable oil commerclally available from Viking 2 1 ~ 1 ~ 2 ~ 33159CA

Chemical Company. In the terminatlng step, carbon dloxlde from a pressurlzed container was admitted to provlde about 0.4 phm csrbon dioxide to the reactor. Water was also added in an amount slightly in stoichiometric excess of the inltiator to separate the lithium residues :
from the polymer chains.
. . .,, ~ .
The antioxidant mixture added in the stabilizing step contained a hlndered phenol [octadecyl 3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate, commerclally available ~.:: ~:
as Irganox~ 1076 from Clba-Geigyl and an organlc phosphlte (trisnonylphenyl phosphite, avsilable &S TNPP from GE Speclalty Chemlcals). Esch stabillzer was dlssolved separAtely in cyclohexane and mixed together. Enough of the mlxture was added to the reactor to provide 0.25 phm hindered phenol snd 1 phm organic phosphite. In auns 1 and 2 a microcrystalllne wax (~E Square~ 195) was also added as an : ,, sntiblocklng agent.
After each addition of monomer, inltiator or sdditive, the feed lines were rinsed with approximately 10-20 phm cyclohexane solvent and cleared with a nitrogen sparge.
Following the stabilization step, each copolymer solution was flashed at 178-180~C to remove a portlon of the diluent. Substantially all of the r~ n~ng diluent was removed in a vacuum oven by drying at 90~C for one hour. The resulting polymer was chopped in a granulator lnto crumb size and then drled for an addltional hour in a vacuum oven.
In each of the four runs (1, 2, 3, and 4), 1500 g total monomers (butadiene and styrene) were used. About 76 weight percent of the total amount of cyclohexane diluent (3130 g) was cbarged lnltlally.
The L~m~in~ng cyclohexane dlluent wa~ added during the run as a dlluent 2 ~
f~ 33159CA

or flush for the varlous reactants added in subsequent steps. In these four polymerlzations, the weight ratlo of total monomers charged was 75/25 styrene/butsdiene.
The charges flnd the results of the runs are summarized in Table 8. Tapered butadiene/styrene bloc~s were formed in step 3 by charglng both butadiene flnd styrene monomers. The charging sequence used was i, S1, i, S2, Bl/S3, coupling flgent. The monomer ratios corresponding to the S1, S2, Bl/S3 sequence were 40, 10, 25/25. Weight ratios of amounts of initiator used in the first two steps of each of the four runs was kept constflnt at 1:1, but the amounts were decreased from 0.08 phm in run 1 to 0.055 phm in run 4 to provide a series of decreasing melt flow resins.
The devolfltilized copolymers from runs 1, 2, 3, and 4 were designated invention copolymers 1, 2, 3 and 4, and had melt flows of 39.1 g/10 min, 19.0 g/10 min, 9.0 g/10 min flnd 4.B g/10 mln, respectively. The differences in melt flows were attributable to dlfferences ln amounts of lnitiator used in each of the four runs.

" ' ':
,' ~"'';

; s "~ "~ " ~ " ~ "

213~.~2~ 33159US

Invention Runs - First Embodiment Component~a Run 1 Run 2 Run 3 Run 4 Step 1 Cyclohexane, phm 145 145 145 145 Tetrahydrofuran, phm 0.04 0.04 0.04 0.04 '-~
n-Butylllthium lnltiator, phm 0.08 0.07 0.06 0.055 Styrene, phm 40 40 40 40 Polymerizatlon Tlme, min 12 12 12 12 Peak Polymerizatlon Temperature, ~C 82 81 85 85 ~ -~
Step 2 n-Butyllithium initiator, phm 0.08 0.07 0.06 0.055 Styrene, phm 10 10 10 10 ~-Polymerlzatlon Tlme, min 12 12 12 12 Peak Polymerization Temperature, ~C 67 70 71 70 Step 3 Butadlene, phm 25 25 25 25 Styrene, phm 25 25 25 25 Polymerization Tlme, min 16 16 16 16 Peak Polymerization Temperature, ~C 122 122 122 116 Step 4 (Coupling) -~
Vikoflex 7170, phm 0.4 0.4 0.4 0.4 Time, min 16 16 16 16 T~~eraLule, ~C 94 93 90 93 Step 5 (Terminstln~) Water, phm 0.2 0.2 0.2 0.2 Carbon Dioxide, phm 0.4 0.4 0-4 0-4 Time, min 25 25 25 25 Temperature, ~C 80 93 87 81 Step 6 (Stabilizin~) i Stabilizer Mixture, phm 1.25 1.25 1.25 1.25 BE Square wax 0.15 0.15 0.15 0.15 Time, min 5 5 5 5 Temperature, ~C n.a. n.a. 84 n.a.

~ t 3 'L 3 2 ~ 33159US
-~ 37 TABLE 8 (Contlnued) Invention Runs - Flrst Embodiment C~ entsa Run 1 Run 2 Run 3 Run 4 Recovered Resin Helt Flow, g/10 min 39.1 19.0 9.0 4.8 Mw/Hn, tholl~An~c 105/63 108/53 ~28/65 143/91 Hetsrogeneity Index 1.67 2.05 1.97 1.57 ~After each additlon of monomer, lnitlator or additive, the feed lines were rinsed with approximately 5-20 phm cyclohexane diluent and clenred with nitrogen. -E~ample II
Thrse more polymerization runs were carried out according to the flrst embodiment of the present invention to demonstrate the effects of varying the weight ratio of smount3 of initiator in each of the two initiator charges. The charges and results of the runs are shown in Table 9. Again, the weight ratio of styrene to butadiene charged was 75 ~-to 25. Samples were made with i, S~, i, S2, Bl/S3 addition sequence followed by coupling; monomer ratios of 40, 10, 25/25 were used.
In each of the three run~ of this example, 0.03 phm lnitiator was charged in the first step. The amount of initiAtor charged in the second step was uaried from 0.08 phm (run 5) to 0.95 phm (run 7) for a range of ratios of amount of initiator in first step to ~mount in second step from 1:2.7 (run 5) to 1:3.2 (run 7). ~ d~
Copolymers from runs 5, 6 and 7 were devolatilized to form invention copolymers 5, 6 and 7, which had melt flows of 5.0 g/10 min, 5.4 g/10 min, and 7.1 g/10 min, respectlvely.
'"~

, -,~ . ..

..::..

2 ~ 3 '1 ~ 2 ~ 33ls9~s ;

Invention Runs - Flrst Embodiment Component~a Run 5 Run 6 Run 7 :~

Step 1 Cyclohexane, phm 145 145 145 Tetrahydrofuran 0.04 0-04 0-04 ::-n-8utyllithlum 0.03 0.03 0-03 initlator, phm :::
Styrene, phm 40 40 40 Polymerlzatlon Tlme, mln12 12 12 Peak Polymerizatlon ~-Temperature, ~C 77 79 76 -~
Peak Polymerizatlon Pressure, psl Step 2 -n-Butylllthlum 0.08 0.085 0.095 ~ :
lnltiator, phm Styrene, phm 10 10 10 Polymerlzation Time, mln12 12 12 Peak Polymerizatlon Temperature, ~C 64 71 65 Step 3 Butadlene, phm 25 25 25 :~
Styrene, phm 25 25 25 Polymerlzatlon Tlme, mln16 16 16 Peak Polymerlzatlon Temperature, ~C 117 121 111 Step 4 (Couplin~) Vlkoflex 7170, phm 0.4 0.4 0.4 Tlme, ~ln 16 16 16 T. ~raLure, ~C 88 87 89 Step 5 (TermlnatlnR) Water, phm 0.2 0.2 0.2 Carbon Dioxide, phm 0.4 0.4 0-4 Time, mln 25 25 25 :~
Trq~3ra~ure, ~C 82 82 84 , 2~34~2~ 33159~)S
,, .-'' 39 TABLE 9 (Continued) Inventlon Runs - First Embodiment Componentsa Run 5 Run 6 Run 7 ~-Step 6 (Stablllzin~) -Stabillzer Mixture, phm 1.25 1.25 1.25 BE Square W8X 0.15 0.15 0.15 Tlme, mln 5 5 5 Recovered Resin Melt Flow, g/10 min5.0 5.4 7.1 Mw/Mn, thousands 181/114 177/111 138/93 Heterogeneity Index1.6 1.6 1.69 ~.

aAfter each addltion of monomer, inltlator or additive, the feed lines were rlnsed with approxlmately 5-20 phm cyclohexane diluent and cleared with nitrogen. :~

Lx~mple III
To demonstrate the second embodiment of this invention, three more polymerization runs were carrled out according to the procedures described ln Example I, wlth the exceptlon that the sequences and amounts of charges were as shown ln Tsble 10. Tapered butadiene/styrene blocks were formed in the third and fourth steps by charging a mixture -.
::...:~ :, of butadlene and styrene monomers. The monomer addltion sequence was i, ~l, l, S2, Bl/S~, B2/S~ followed by coupling; the monomer weight ratios were 40, 10, 12.5/12.5, 12.5/12.5, respectively. The polymers were 75 :
percent styrene and 25 percent butadlene.
In eQch of the three runs of this example the weight ratio of amount of initiator in the first step to the amount in the second step was kept constant at 1:1 with the absolute amount varied from 0.06 phm (run 8) to 0.055 phm (run 10).

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The copolymers produced ln the three runs were designated invention copolymers 8, 9, and 10, and had melt flows of 14.3, 6.40 and :~
10.8 respectlvely. It is believed that lower melt flows are attributable to lower amounts of initlator. The polymerizations of :
invention runs 8, 9 and 10 are shown in Tabl~ 10.

. ., Invention Runs - Second Embodiment ~:
Cc... .ehtsa Run 8 Run 9 Run 10 ~ ;

Step 1 Cyelohexane, phm 145 145 145 Tetrflhydrofuran, phm 0.04 0.04 0.04 n-Butylllthlum 0.06 0.05 0.055 inltlator, phm Styrene, phm 40 40 40 Polymerizatlon Tlme, mln 12 12 12 Peak Polymerlzatlon ~ .~' Ta eraLure~ ~C 85 82 . 84 Step 2 n-Butylllthium 0.06 0.05 0.055 ~ -lnltlator, phm Styrene, phm 10 10 10 :~
Polymerlzation Tlme, mln 12 12 12 ~
Peak Polgmerlzatlon ~ ~ -T~sla~ule, ~C 69 69 70 Step 3 ~ ~ :
Butadiene, phm 12.5 12.5 12.5 Styrene, phm 12.5 12.5 12.5 Polymerizatlon Time, mln 16 16 16 Peak Polymerlzatlon ~*
TP .~a~ure~ ~C 84 83 84 : Step 4 Butadlene, ph~ 12.5 12.5 12.5 Styrene, phm 12.5 12.5 12.5 Polymerization Time, min 16 16 16 ~ Peak Polymerlz~tion Temperature, ~C 96 102 102 ~;
'':
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TABLE 10 (Continued) Invention Runs - Second Embodiment ComponentsaRun 8 Run 9 Run 10 Step 5 (CouplinR) Vlkoflex 7170, phm 0.4 0.4 0.4 Time, min 16 16 16 Temperature, ~C 82 89 89 Step 6 (Termin~tin~) Water, phm 0.2 0.2 0.2 Carbon Dioxide, phm 0.4 0.4 0.4 Time, min 25 25 25 Temperature, ~C 80 82 82 Step 7 (Stabilizing) Stabilizer Mixture, phm 1.25 1.25 1.25 Antiblocking agent, phm 0.15 0.15 0.15 Time, min 5 5 5 Temperature, ~C 80 n.a. 81 Recovered Resin Melt Flow, g/10 min 14.3 6.4 10.8 Mw/Mn, thousands 154/104 173/115 147/91 Heterogeneity Index 1.48 1.50 1.62 ~After each addition of monomer, lnltlsitor or addltive, the feed lines were rinsed with approxlmately 5~20 phm cyclohexane dlluent and cleared wlth nltrogen. -~
~ :..",, ''..'. '.' E~ample IV ;~
Two comparative polymers were used for CompflriSOnS of physicsl properties of blends made with pol~ ene. Comparative polymer 11 was a reslnous styrene-butadiene copolymer with a melt flow of 8.4 g/10 min. -Polymer 11 was polymodal from multiple initiator and monomer charges (S, 1, 1, S, B, i, S, B) and coupled with an epo~ ed vegetable oil coupllng agent. Polymer 11 contained nomlnally 75 wt % styrene and 25 - ~
wt % butsdiene with no styrene/butadiene t~pered blocks. Polymer 11 ~ -forms 50:50 by welght blends with polystyrene that have hlgh blueness ~-nnd modest physical properties.

3 ~ ~ 2 ~ 33159US

Compsratlve polymer 12 was a styrene-bu~adiene copolymer with no tapered block segments. ~olymer 12 contained nominally 75 wt %
styrene ~nd 25 wt % butadiene and had ~ melt flow of 8.8 g/10 min. It had A polymodal molecular weight from multiple lnitiator and monomer charges (S, i, i, S, B) ~nd was coupled with an epoxidized vegetable oll coupllng agent. Polymer 12 formed 50:50 blends by weight with polystyrene that have low bll]eness and modest impact properties.

ExamPle V
A sQrles of blends of the invention polymers from Examples I
and II Wa8 prepared with Novacor~ 555 general purpose polystyrene to demonstrate the properties of blends of copolymers containing a single tapered block (lnvention embodiment 1). Polymer S was not included in the blend series slnce it had a melt flow essentially the same as that of polymer 4. Polymers 11 and 12 were also blended wlth poly~yiene for compflrison.
The blends were 50:50 by weight and were prepared by solution - .;
blending in cyclohexane in a reactor at 100~C with stirring for one hour. Each solutlon was fl~shed to remove the solvent ~nd the polymer was dried, chopped in a grsnulator, and dried again. The dry polymer was processed on a roll mill and chopped again before inJectlon molding on an Arburg model 90 in~ection molder with zones 1, 2, 3, and nozzle at 210~C, 210~C, 220~C, and 210~C, respectively, to make specimens to test for propertles.
For convenient reference, blends are designatet as blends with the cor.es~vl,ding polymer number and a prime. For example, a blend prep~red from polymer I and poly~ienc i9 blend 1' and a blend prepared from polymer 2 and poly~yiene is desi8nated blend 2'.

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The blend test results are shown in TAble 11. Test specimens made from the first four blends had less blueness than test specimens made from the comparative polymers. Specimens made from blends 6' and 7' had essentially the same btueness a9 specimens made from blend 12'.
Test specimens made from blends 1', 2', 3', 4 , and 6' had Izod impact values higher than those mflde from comparative blends 11' and 12'. Test specimens made from blend 7' had a lower Izod impact value than those made from the other blends. It is possible that the hlgh level of lnltlator ln step two of the polymerizatlon of polymer 7 .. .....
and the resultlng hlgher melt flow of the flnal resln prevented ~I ~v.~r~ t ln the Izod impact value of Arburg test specimens made from blends polymer 7. ;
Test specimens made from blends 1', 2', and 3' had higher haze values and speclmens made from blends 1' and 2' had hlgher melt flows than those made from the other blends.

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~ 45 Example VI
A serles of blends of double tapered block invention polymers ~ -~
(second invention embodiment~ wlth polystyrene WAS preparet to demonstrste the propertles of flrtlcles mflde from the blends. Copolymers 8, 9, and 10 from Example ITI were blended flS described in Example V in 50:50 by weight mixtures with general purpose polystyrene to form blends 8', 9', and 10'. Test specimens were in~ection molded from the blends . ~ ~.
as described in Example V. .
The results (Table 12) show that flrticles made from blends of :~
lnvention polymers 8, 9, and 10 had better Izod impact values than those '' made from comparatlve blends 11' and 12' (shown in Table 11). Articles made from blends of the lnventlon polymers also have less blueness than those made from comparative blend 11'. '-, . ..,: ~ "

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46 ~-Physical Properties of Polymer Blends With Polystyrenea Invention Invention InventionComparative ~lend Blend Blend ~lend Property 8' 9' 10' 11' Styrene-butadiene copolymer 8 9 10 11 .' ; ' Blend melt : ~.
flow, g/10 mln 14.8 12.0 14.8 16.8 ' :~

Haze, % 4.1 4.0 5.1 4.3 Hunter blueness, b -17.9 -18.5 -17.9 -20.3 Shore D hardness 76 77 76 77 Notched Izod impact, J/m14.9 17.1 19.2 12.3 Vicat softening, ~C 89.3 90.5 90.5 85.3 Tenslle Strength ' yield HPa 43.2 43.9 42.5 37.8 break MPa 28.6 28.7 28.7 28.0 Elongatlon yleld, X 6.4 6.5 6.5 4.8 break, % 17.9 16.7 13.6 32.0 Flexural modulus, MPa1988 1949 1986 1979 a50:50 S~ylene butadiene copolymer:polystyrene Exaeple VII
Three more invention copolymers were prepared on a larger scale to demonstrate further the effect of two butadiene/styrene tapered blocks in improvlng impact properties of articles msde from blends of the invention copolymers with poly~iene. These polymerizations varied " ';, ; 7 ~ i i ' ~ , I i . t~
~ S~ f~

~ 2~3~026 33159CA
,. 47 the size of the two tapered blocks and the weight ratlos of initiator charges. The polymerizations were carrled out in a 380 L reactor. ;~
The polymer polymerizatlon recipes are shown in Table 13.
Each polymer was prepnred with the sequence i,S,i,S,B/S,~/S. Polymer 13 had monomer charge welght ratios of 40, 10, 6.9/7.8, 18.1/17.2. Polymer 14 had monomer charge weight ratlos of 40, 10, 5.9/10, 19.1/14.4. ;
Polymer 15 had monomer charge ratlos of 40, 10, 5.9/10, 19.1/14.4.
Monomer charge ratios for polymers 14 and 15 do not add up to 100 phm ~ ~
because of charge irregulArities; phm indicated above was that actually '' charged. The initiator weight ratlos for steps 1:2 ln polymerizations 13, 14, and 15 were 1:0.79, 1:0.92, and 1:0.89, respectlvely. ~ - ' Flow rates for the three polymers were 7.0, 11.5, and 13.7 g/10 min.

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. 48 TABLE 13 :~
Invention Runs - Second Embodiment Run 13 Run 14 Run 15 ~
~ ':
Step 1 Cyclohexsne, phm 168.9 168.9 168.9 Tetrahydrofur~n, phm.04 .04 0.04 n-~utylllthium initi~tor, phm 0.061 0.061 0.065 Styrene, phm 40 40 40 Cyclohexane, phm 1.1 1.1 1.1 Peak Polymerization Temperature, ~C 83 83 83 Peek Polymerization Pressure, psi 31 32 30 .
Step 2 n-Butyllithium Initiator, phm 0.048 0.056 0.058 ~:
Styrene, phm 10 10 10 Cyclohexane, phm 1.1 1.1 l.l Peak Polymeriz~tion Temperature, ~C 81 82 82 Peak Polymerization Ple~ure, psi 35 37 34 Step 3 ~utatlene, phm 6.9 5.9 5.9 Styrene, phm 7.8 10 10 Cyclohexane, phm 1.1 1.1 1.1 ~ -Peak Polymerization Temperature, ~C 110 109 109 Peak Polymerizstion P aEsule, psi 57 58 55 ~ Step 4 Hutadiene, phm 18.1 19.1 19.1 Styrene, phm 17.2 14.4 14.4 Cyclohexane, phm l.l 1.1 l.l Peak Polymerlzation Temperature, ~C 95 98 97 Peak Polymerlzatlon ~ .
PLe~re, psi 52 54 50 . . .
- -..

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TABLE 13 (ContiDued~
Invention Runs - Second Embodiment Run 13 Run 14 Run 15 Polymer An~lysis (prior to couping) :.
Mw/Mn, thousAndsa (GPC Area composition)b Peak 1 104/99 (64) 100/95 (63) 95/90 (64) Peak 2 50/46 (36) 47/44 (37) 46/43 (36) ~:~
Step 5 (Couplin~) : R
Vikoflex 7170, phm 0.4 0.4 0.4 ' Cyclohexsne, phm 0.55 0.55 0.55 :~ :
Temperature, ~C 88 86 88 Pressure, psi 50 52 48 Step 6 (Termlnatlng) W~ter, phm 0.2 0.2 0.2 Carbon Dloxide, phm0.1 0.1 0.1 ::
Tempersture, ~C 87 87 87 Pressure, psi 50 50 50 .
Step 7 (Stabillzin~) Stabllizer Mixture, phm 1.25 1.25 1.25 Antlblocklng agent, phm 0.3 0.3 0-3 M
Recovered Resln Melt Flow, g/10 min7.0 11.5 13.7 :~

~PO1~ Lene equivAlent Mw/Mn. Mw/Mn of polystyrene with the ssme hydrodynamic volume a5 the polymer pesk.
bResponse of a dielectric detector in an Applied Automation process control GPC.

E~CBmP1e VIII
Two comp~rative polymers (16 And 17) were prep~red for compArlson with the invention polymers from Example VII. Polymer 16 Wh8 ~ :
coupled polymodal ~tyrene/butadlene copolymer cont~ining 75 wt X
styrene and 25 wt % but~diene. Polymer 16 was prepared wlth the ~.-d ' ~

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sequence l,S,l,S,B/S,l,S,B using monomer charge weight ratios of 37, 19, 7.5/5, 14, 17.5, respectively.
Polymer 17 was a coupled polymodal styrene/butadlene copolymer ~ -contalnlng 70 wt % styrene flnd 30 wt % butadiene. Polymer 17 was prepared with the sequence i,S,i,S,B,l,S,B using monomer charge welght ratlos of 37, 19, 9, 14, 21, respectlvely.
These comparat~ve polymers were prepflred ln a 380 L reactor accordlng to the procedure ln Table 14.
Polymer 16 yielded blends with polystyrene which were made into test speclmens that had low blueness and modest physical properties. Polymer 17 formed blends wlth polystyrene which were made into test speclmens that had hlgh blueness and good physical properties.
The flow rates for polymers 16 and 17 were 8.2 and 8.6 g/10 min, respectively.

f - ~ 21~ 33159CA

TABIE'. 14 - ~h Invention Runs - Second Embodiment ~ -.
Componentsa Run 16Run 17 , . :--Step 1 :
Cyclohexane, phm 168 168 ~ :
Tetr.shydrofurAn, phm 0.02 0.02 n-Butylllthium initiator, phm 0.034 0.031 Styrene, phm 37 37 Peak Polymerization Temperature, ~C 88 87 ~ ::
Peak Polymerlzation Pressure~ psi 37 36 :~ ~:
Step 2 n-Butyllithium 0.048 0.053 initiator, phm Styrene, phm 19 19 Peak Polymerlzatlon :
Temperature, ~C 86 85 Peak Polymerization Pressure, psi 33 32 :~
Step 3 -Butadiene, phm 7.5 9 Styrene, phm 5 0 Peak Polymerlzation Temperature, ~C 82 83 Peak Polymerization Pressure, psi 37 36 :~
Step 4 n-Butyllithlum initiator, phm 0.085 0.110 Styrene, phm 14 14 Peak Polymerization .
Temperature, ~C 87 8S :
Peak Polymerizatlon Pressure, psi 41 40 -Step 5 Butadiene 17.5 21 Peak Polymerizatlon T~ml)er.s~ure, ~C 101 107 Peak Polymerization Pressure, ~C 54 58 Step 6 (CouPlinR) Vikoflex 7170, phm 0.4 0.4 T:m~-ra~u~e~ ~C 89 95 :~
Ples~u~e, psi 51 54 ~ -''','~:~
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TABLE 14 (Contlnued) Invention Runs - Second Embodiment Componentsa Run 16 Run 17 Step 7 (Terminating) Water, phm 0.2 0.2 Csrbon Dioxide, phm 0.1 0.1 Temperature, ~C 87 87 Pressure, p9i 50 50 Step 8 (Stabilizin~) Stabilizer Mixture, phm 1.25 1.25 Antiblocking flgent, phm 0.3 0.3 Recovered Resin Melt Flow, g/10 min 8.2 8.6 aAfter eflch addition of monomer, initiator or additive, the feed lines were rinsed with approximately 5-20 phm cyclohexane diluent ~nd cleflred with nitrogen.

E~anple IX
Polymers from Examples VII and VIII were blended with Novflcor~
555 general purpose poly~Lyiene to produce blends 13', 14', 15', 16', and 17' for evaluation. The resu]ting blend was extruded on an 8.9 cm ;
dlameter extruder and sheet line. All blends were 50:50 by weight except for blend 16', which was a 60:40 copolymer:polystyrene by weigbt blend. A 0.51 mm die gap opening was used for the preparation of a 0.38 mm thick extruded sheet for evaluation.
The extruded sheet samples were evaluated and the results are shown in Table 15. The fold test involves bending the sheet on itself in the machine direction (MD) to induce fl transverse directional (TD) breflk. The sheet i8 folded flt two dlfferent rAtes to allow differentlfltion between brittle shest sflmples. In flddition, the ~ !"~, "; , ~

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behavior of the sheet in response to a teflr in mflchine and transverse directions was determined.
Sheets msde from invention blends 13', 14' and 15' All had less blueness than sheets made from comparatlve blend 17', but more blueness than sheets made ~rom comparativs blend 16'.
Sheets made from blent 13' had the highest total energy dart drop value of sheets from this set of blends. Sheets made from blends 14' and 15' had low total energy dart drop values simllar to the values of sheets made from blend 16'. Sheets made from comparfltiVe blend 16' had the lowest blueness value of any ln the group, but had a low total energy dart drop value and brittle fold test. Sheets made from comparative blend 17' had the highest blueness value and better ductility than invention blends 14' and 15'.

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fi Physlcal Properties of Polymer Blends With Polystyrene Invention Inventlon Invention Comparfltive Comparative Property Blend Blend Blend Blend Blend 13' 14' 15' 16' 17' Styrene-butadiene copolymer 13 14 15 16 17 Copolymer:Styrene blend ratio 50:50 50:50 50:50 60:40 50:50 Hunter blueness b-8.0 -10.0 -10.1 -5.7 -13.5 Haze, % 2.46 2.48 2.97 1.63 3.60 Transmission, % 89.6 89.3 89.2 89.8 88.8 Total energy dart .
drop, J 3.17 0.80 1.11 0.95 1.61 ' .

Transver~e dlrection : ' Fold (fast/slow) D/D B/D B/D B/B D/D ' Machine direction Tesr~ D D D D D

Tr&n~ve~e directlon ;~
Tear D D D D D

~D=ductile, B=brittle.

These results show thflt either of the embodiments of the :~
inventlon cAn be used in blends with polymers of styrene to produce resins from whlch can be made articles havlng low blueness and othér properties comparable to or better than the properties of articles made from blends of polymers of styrene wlth other monovinylaromatic/con~ugated diene copolymers. More particularly, a comparison of the 50:50 (copolymer:styrene) invention blends 13', 14' .:

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:;
.J.i 55 and 15' wlth the 60:40 (copolymer:styrene) comparative blend 16' shows that 8 smaller amount of lnvention copolymer than comparatlve copolymer can be used to show comparflble improvements in reduction of blueness.
Other surprising blend properties are demonstrsted by these runs. For example, invention blend 13' which had a total of about 75 wt Z total styrene in the blend composition had total energy dart drop of 3.17 J
compared to a total energy dart drop of 1.61 J for comparative blend 17' which had only about 70 wt 1 total styrene in the blend composition.
While the polymers and methods of this invention have been described in detsil for the purpose of illustrfltion, the inventive polymers and methods are not to be construed as limited thereby. This patent is intended to cover fl II changes and modifications within the ~-spirit and scope thereof.

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Claims (65)

1. A method of preparing a polymer under solution polymerization conditions in a reaction zone comprising:
(a) charging a monovinylaromatic monomer and an initiator and in the presence of a randomizer allowing polymerization to occur until essentially no free monomer is present; thereafter (b) charging an initiator and a monovinylaromatic monomer, and allowing polymerization to occur until essentially no free monomer is present; thereafter (c) charging a mixture of monovinylaromatic monomer and conjugated diene monomer, and allowing polymerization to occur until essentially no free monomer is present; and thereafter (d) charging the reaction mixture with a coupling agent.

2. A method according to claim 1 wherein each said monovinylaromatic monomer contains 8 to 12 carbon atoms and each said conjugated diene contains 4 to 6 carbon atoms, said monomers being added in a ratio of about 55 to about 95 weight percent monovinylaromatic monomer and about 5 to about 45 weight percent conjugated diene monomer, thus giving a resinous tapered block copolymer.

3. A method according to claim 1 wherein each said monovinylaromatic monomer contains 8 to 12 carbon atoms and each said conjugated diene contains 4 to 6 carbon atoms, said monomers being added in a ratio of about 60 to about 90 weight percent monovinylaromatic monomer and about 10 to about 40 weight percent conjugated diene monomer, thus giving a resinous tapered block copolymer.

4. A method according to claim 1 wherein each said monovinylaromatic monomer contains 8 to 12 carbon atoms and each said conjugated diene contains 4 to 6 carbon atoms, said monomers being added in a ratio of about 65 to about 85 weight percent monovinylaromatic monomer and about 15 to about 35 weight percent conjugated diene monomer, thus giving a resinous tapered block copolymer.

5. A method according to claim 1 wherein the weight ratio of the amounts of said monovinylaromatic monomer and said conjugated diene monomer in step (c) is within the range of about 1:0.63 to about 1:2.

6. A method according to claim 1 wherein the weight ratio of said monovinylaromatic monomer and said conjugated diene monomer in step (c) is within the range of about 1:0.67 to about 1:1.8.

7. A method according to claim 1 wherein the weight ratio of said monovinylaromatic monomer and said conjugated diene monomer in step and (c) is within the range of about 1:0.8 to about 1:1.5.

8. A method according to claim 1 wherein said monovinylaromatic monomer charged in step (a) is from about 27 to about 80 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (b) is from about 5 to about 21 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (c) is from about 7 to about 60 weight percent of the total monovinylaromatic monomer charged in said method.

9. A method according to claim 1 wherein said monovinylaromatic monomer charged in step (a) is from about 40 to about 67 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (b) is from about 8 to about 19 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (c) is from about 27 to about 40 weight percent of the total monovinylaromatic monomer charged in said method.

10. A method according to claim 1 wherein said monovinylaromatic monomer charged in step (a) is from about 47 to about 60 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (b) is from about 11 to about 16 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (c) is from about 29 to about 37 weight percent of the total monovinylaromatic monomer charged in said method.

11. A method according to claim 1 wherein said initiator in steps (a) and (b) is charged in amounts effective to provide proportionate amounts of polymeric species in said polymer such that articles made from blends of said polymer with polymers of styrene have improved impact strength.

12. A method according to claim 1 wherein said initiator in steps (a) and (b) is charged in amounts effective to provide proportionate amounts of polymeric species in said polymer such that articles made from blends of said polymer with polymers of styrene have low blueness.

13. A method according to claim 1 wherein said initiator in steps (a) and (b) is charged in amounts effective to provide polymer having a melt flow in the range from about 2 to about 50 g/10 min.

14. A method according to claim 1 wherein said initiator in step (b) is present in an amount at least equal to the amount of said initiator in step (a).

15. A method according to claim 1 wherein the amount of initiator in step (b) is from about 0.25 to about 300 times as much, based on weight as the amount of initiator in step (a).

16. A method according to claim 1 wherein the amount of initiator in step (b) is from about 0.3 to about 10 times as much, based on weight, as the amount of initiator in step (a).

17. A method according to claim 1 wherein each said conjugated diene monomer is 1,3-butadiene, each said monovinylaromatic monomer is styrene, said organomonoalkali metal initiator is n-butyllithium, said randomizer is one chosen from the group of tetrahydrofuran and diethyl ether, and said coupling agent is epoxidized vegetable oil.

18. A method according to claim 1 wherein polymerization is carried out in a hydrocarbon diluent;
wherein said polymerization is carried out in a substantial absence of oxygen and water at temperatures ranging from about -10°C to about 150°C;
wherein, after said coupling agent reacts with products of said polymerization, the system is treated with a terminating agent and a stabilizer; and wherein, after termination with said terminating agents, any remaining hydrocarbon diluent is flashed off.

19. Polymodal copolymers produced in accordance with the method of claim 1.

20. Articles made from the polymer of claim 19.

21. A polymodal coupled resinous block copolymer of a monovinyl aromatic compound and a conjugated diene, said copolymer having polymer chains which result from coupling S-S-B/S-Li S-B/S-Li wherein S = monovinylaromatic block B = conjugated diene block B/S = tapered block Li = living polymer site or coupling site.

22. A copolymer as recited in claim 21 having from about 55 to about 95 weight percent polymerized monovinylaromatic monomer based on total weight of monomers in said copolymer.

23. A copolymer as recited in claim 21 having from about 60 to about 90 weight percent polymerized monovinylaromatic monomer based on total weight of monomers in said copolymer.

24. A copolymer as recited in claim 21 having from about 65 to about 85 weight percent polymerized monovinylaromatic monomer based on total weight of monomers in said copolymer.

25. Articles made from the copolymer of claim 21.

26. Blends of a polymer of styrene and the copolymer of claim 21.

27. A blend as recited in claim 26 wherein said polymer of styrene is present in an amount in the range from about 10 weight percent to about 70 weight percent, based on total weight of said blend.

28. A blend as recited in claim 26 wherein said polymer of styrene is present in an amount in the range from about 20 weight percent to about 65 weight percent, based on total weight of said blend.

29. A blend as recited in claim 26 wherein said polymer of styrene is present in an amount in the range from about 30 weight percent to about 60 weight percent, based on total weight of said blend.

30. Articles made from the blend of claim 26.

31. A method of preparing a polymer under solution polymerization conditions in a reaction zone comprising:
(a) charging a monovinylaromatic monomer and an initiator and in the presence of a randomizer allowing polymerization to occur until essentially no free monomer is present; thereafter (b) charging an initiator and a monovinylaromatic monomer, and allowing polymerization to occur until essentially no free monomer is present; thereafter (c) charging a mixture of monovinylaromatic monomer and conjugated diene monomer, and allowing polymerization to occur until essentially no free monomer is present; thereafter (d) charging a mixture of monovinylaromatic monomer and conjugated diene monomer, and allowing polymerization to occur until essentially no free monomer is present; and thereafter (e)charging the reaction mixture with a coupling agent.

32. A method according to claim 31 wherein each said monovinylaromatic monomer contains 8 to 12 carbon atoms and each said conjugated diene contains 4 to 6 carbon atoms, said monomers being added in a ratio of about 55 to about 95 weight percent monovinylaromatic monomer and about 5 to about 45 weight percent conjugated diene monomer, thus giving a resinous tapered block copolymer.

33. A method according to claim 31 wherein each said monovinylaromatic monomer contains 8 to 12 carbon atoms and each said conjugated diene contains 4 to 6 carbon atoms, said monomers being added in a ratio of about 60 to about 90 weight percent monovinylaromatic monomer and about 10 to about 40 weight percent conjugated diene monomer, thus giving a resinous tapered block copolymer.

34. A method according to claim 31 wherein each said monovinylaromatic monomer contains 8 to 12 carbon atoms and each said conjugated diene contains 4 to 6 carbon atoms, said monomers being added in a ratio of about 65 to about 85 weight percent monovinylaromatic monomer and about 15 to about 35 weight percent conjugated diene monomer, thus giving a resinous tapered block copolymer.

35. A method according to claim 31 wherein the weight ratio of the amounts of said monovinylaromatic monomer and said conjugated diene monomer in each of steps (c) and (d) is within the range of about 1:0.63 to about 1:2.

36. A method according to claim 31 wherein the weight ratio of said monovinylaromatic monomer and said conjugated diene monomer in each of steps (c) and (d) is within the range of about 1:0.67 to about 1:1.8.

37. A method according to claim 31 wherein the weight ratio of said monovinylaromatic monomer and said conjugated diene monomer in each of steps (c) and (d) is within the range of about 1:0.8 to about 1:1.5.

38. A method according to claim 31 wherein said monovinylaromatic monomer charged in step (a) is from about 27 to about 80 weight percent of the total monovinylaromatic monomer charged in said method, and wherein said monovinylaromatic monomer charged in step (b) is from about 5 to about 21 weight percent of the total monovinylaromatic monomer charged in said method;
and wherein said monovinylaromatic monomer charged in step (c) is from about 3 to about 19 weight percent of the total monovinylaromatic monomer charged in said method;
and wherein said monovinylaromatic monomer charged in step (d) is from about 13 to about 36 weight percent of the total monovinylaromatic monomer charged in said method.

39. A method according to claim 31 wherein said monovinylaromatic monomer charged in step (a) is from about 40 to about 67 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (b) is from about 8 to about 19 weight percent of the total monovinylaromatic monomer charged in said method;
and wherein said monovinylaromatic monomer charged in step (c) is from about 5 to about 16 weight percent of the total monovinylaromatic monomer charged in said method;
and wherein said monovinylaromatic monomer charged in step (d) is from about 16 to about 32 weight percent of the total monovinylaromatic monomer charged in said method.

40. A method according to claim 31 wherein said monovinylaromatic monomer charged in step (a) is from about 47 to about 60 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (b) is from about 11 to about 16 weight percent of the total monovinylaromatic monomer charged in said method; and wherein said monovinylaromatic monomer charged in step (c) is from about 8 to about 13 weight percent of the total monovinylaromatic monomer charged in said method;
and wherein said monovinylaromatic monomer charged in step (d) is from about 20 to about 25 weight percent of the total monovinylaromatic monomer charged in said method.

41. A method according to claim 31 wherein said initiator in each of steps (a) and (b) is charged in amounts effective to provide proportionate amounts of polymeric species in said polymer such that articles made from blends of said polymer with polymers of styrene have improved impact strength.

42. A method according to claim 31 wherein said initiator in steps (a) and (b) is charged in amounts effective to provide proportionate amounts of polymeric species in said polymer such that articles made from blends of said polymer with polymers of styrene have low blueness.

43. A method according to claim 31 wherein said initiator in steps (a) and (b) is charged in amounts effective to provide polymer having a melt flow in the range from about 2 to about 50 g/10 min.

44. A method according to claim 31.
wherein said initiator in step (b) is present in an amount at least equal to the amount of said initiator in step (a).

45. A method according to claim 31 wherein the amount of initiator in step (b) is from about 0.25 to about 300 times as much, based on weight, as the amount of initiator in step (a).

46. A method according to claim 31 wherein the amount of initiator in step (b) is from about 0.3 to about 10 times as much, based on weight, as the amount of initiator in step (a).

47. A method according to claim 31 wherein each said conjugated diene monomer is 1,3-butadiene, each said monovinylaromatic monomer is styrene, said organomonoalkali metal initiator is n-butyllithium, said randomizer is one chosen from the group of tetrahydrofuran and diethyl ether, and said coupling agent is epoxidized vegetable oil.

48. A method according to claim 31 wherein polymerization is carried out in a hydrocarbon diluent;
wherein said polymerization is carried out in a substantial absence of oxygen and water at temperatures ranging from about -10°C to about 150°C;
wherein, after said coupling agent reacts with products of said polymerization, the system is treated with a terminating agent and a stabilizer; and wherein, after termination with said terminating agents, any remaining hydrocarbon diluent is flashed off.

49. Polymodal copolymers produced in accordance with the method of claim 31.

50. Articles made from the polymer of claim 49.

51. A polymodal coupled resinous block copolymer of a monovinyl aromatic compound and a conjugated diene, said copolymer having polymer chains which result from coupling S-S-B/S-B/S-Li S-B/S-B/S-Li wherein S = monovinylaromatic block B = conjugated diene block B/S = tapered block Li = living polymer site or coupling site.

52. A copolymer as recited in claim 51 having from about 55 to about 95 weight percent polymerized monovinylaromatic monomer based on total weight of monomers in said copolymer.

53. A copolymer as recited in claim 51 having from about 60 to about 90 weight percent polymerized monovinylaromatic monomer based on total weight of monomers in said copolymer.

54. A copolymer as recited in claim 51 having from about 65 to about 85 weight percent polymerized monovinylaromatic monomer based on total weight of monomers in said copolymer.

55. Articles made from the copolymer of claim 51.

56. Blends of a polymer of styrene and the copolymer of claim 51.

57. A blend as recited in claim 56 wherein said polymer of styrene is present in an amount in the range from about 10 weight percent to about 70 weight percent, based on total weight of said blend.

58. A blend as recited in claim 56 wherein said polymer of styrene is present in an amount in the range from about 20 weight percent to about 65 weight percent, based on total weight of said blend.

59. A blend as recited in claim 56 wherein said polymer of styrene is present in an amount in the range from about 30 weight percent to about 60 weight percent, based on total weight of said blend.

60. Blends of a polymer of styrene and the copolymer of claim 49.

61. A blend as recited in claim 60 wherein said polymer of styrene is present in an amount in the range from about 10 weight percent to about 70 weight percent, based on total weight of said blend.

62. A blend as recited in claim 60 wherein said polymer of styrene is present in an amount in the range from about 20 weight percent to about 65 weight percent, based on total weight of said blend.

63. A blend as recited in claim 60 wherein said polymer of styrene is present in an amount in the range from about 30 weight percent to about 60 weight percent, based on total weight of said blend.

64. Articles made from the blend of claim 56.

65. Articles made from the blend of claim 60.