WO1997038027A1

WO1997038027A1 - A method of multiplication polymerization suitable for use in forming hyperbranched polymer films on a surface

Info

Publication number: WO1997038027A1
Application number: PCT/US1997/005747
Authority: WO
Inventors: Richard M. Crooks; David E. Bergbreiter; Yuefen Zhou; Merlin L. Bruening; Mona Wells
Original assignee: The Texas A & M University System
Priority date: 1996-04-09
Filing date: 1997-04-07
Publication date: 1997-10-16
Also published as: AU2445097A

Abstract

A multiplication polymerization process comprises providing a surface containing a plurality of reactive functional groups, reacting one or more of the reactive functional groups with a mer molecule capable of providing two or more reactive functional groups for each of the reactive functional groups reacted and repeating the foregoing steps until a desired polymeric film is attained. This method can be particularly employed with preparation of a hyperbranched polymer films on surfaces.

Description

TITLE OF THE INVENTION A METHOD OF MULTIPLICATION POLYMERIZATION SUITABLE FOR USE IN FORMING HYPERBRANCHED POLYMER FILMS ON A SURFACE

Field of the Invention The present invention relates to a method of polymerization and, in particular, a method of "multiplication" polymerization which is suitable for use in forming a hyperbranched polymer film on a surface.

Background of the Invention The modification of polymer film surfaces by grafting onto the surface of a substrate typically involves the use of an addition polymerization process. The most commonly employed of the addition polymerization techniques is free-radical polymerization.

Free-radical graft polymerization, as illustrated in Fig. 1, often begins with the modification of the surface on which the graft is to be introduced. In some cases intermediate functional groups are introduced.

Modification of such groups then leads to radical sites. Alternatively radical sites can be formed directly on a substrate. Regardless, upon modification of the surface, the formation of graft polymers by free-radical polymerization basically involves the typical three-stage free-radical polymerization process, i.e., chain initiation, chain propagation, and chain termination. Each of these three stages are notoriously well known and have been studied extensively. While addition polymerization processes are capable of forming a graft polymer film on a surface, the process has certain limitations. For example, as illustrated by Figure 1, the length of the individual graft polymer chains can vary greatly over the treated surface. That is, because formation of each chain is basically an individual "addition" process that occurs until termination, a number of very short and a number of very long polymeric chains are typically formed. Because of this, it is very difficult to provide any uniformity of, or control over, the individual polymer chains grafted onto the polymeric surface.

Accordingly, the need still exists for an improved technique for forming graft polymers on a surface.

Summary of the Invention The present invention is capable of overcoming the limitations associated with traditional addition polymeric methods such as free-radical polymerization.

In contrast to such prior techniques, the process of the present invention is a "multiplication" method of polymerization which comprises providing a plurality of reactive functional groups on a surface, and then reacting one or more of the reactive functional groups with a molecule, which upon reacting with the functional groups, is capable of introducing two or more "new" reactive functional groups, which groups are suitable for subsequent reaction with the molecule. By repeating this sequence of steps a number of times, a polymer film and in particular, a highly branched, or even preferably, hyperbranched polymer film can be formed on a surface. In one embodiment of the invention, the method comprises : (a) providing a plurality of reactive functional surface groups on a surface to be treated,

(b) reacting at least one of the reactive functional groups with a monomer, oligomer or polymer including a plurality of functionalities suitable for forming additional reactive functional groups; (c) converting one or more of the functionalities to additional reactive functional groups; and

(d) repeating (b) and (c) one or more times. As mentioned above, one specific area in which this process can be effectively employed is in the formation of highly branched, and preferably, hyperbranched grafted polymer film. As one example in this area, the process is capable of providing hyperbranched poly(acrylic acid) films on surfaces containing self-assembled monolayers. This hyperbranched polymer film is particularly advantageous insofar as it contains a high density of carboxylic acid groups which can selectively combine with metal ions or reacts with other molecules for subsequent derivatization.

Brief Description of the Drawings Figure 1 illustrates traditional free-radical polymerization onto a surface;

Figure 2 illustrates one example of a polymerization process according to the present invention;

Figures 3-8 illustrate various properties of polymer films produced in the examples.

Detailed Description of the Preferred Embodiments As discussed above, the present invention relates to a multiplication method for polymerization. By "multiplication," we are referring to the fact that, in contrast to traditional addition polymerization processes, the present invention involves a process which, through the use of a suitable oligomer or polymer, allows for each reactive functional group that is reacted to be "replaced" with two or more reactive functional groups. Accordingly, polymeric films produced by way of such a process grow in discrete steps. However, unlike most "layer by layer" approaches to polymerization, film thickness can increase nonunearly as a function of the number of layers and the branched polymeric architecture.

Moreover, this process allows for the preparation of thin, graft polymer films of highly branched, and preferably hyperbranched, polymers. Hyperbranched polymers are known in the art. In the past, hyperbranched polymers have also received a variety of other descriptive names, e.g., cauliflowers, combburst polymers and the like. As employed herein, the term, in effect, refers to a subset of the class of polymers known as dendrimers . Hyperbranching of polymers is of considerable interest insofar as it amplifies the number of functional groups on the treated surface. Moreover, hyperbranched polymers contain a high density of reactive functional groups. Accordingly, when suitable functional groups such as carboxylic acid groups are employed, they can selectively bind metal ions and can serve as reactive sites for subsequent derivatization. Thus, the polymer films so produced can be very relevant in the area of boundary layer phenomena such as adhesion, wetting, and chemical sensing.

In one preferred embodiment of the present invention, a hyperbranched polymeric film grafted on self-assembled monolayers is produced. Although the present invention will be discussed largely in terms of this preferred embodiment, the process is in no way limited to this environment. Instead, as will be seen, this method can be effectively employed in the production of a wide variety of polymer grafts.

As discussed above, the method involves reaction of suitable reactive sites of the surface or reactive functional groups that are attached to a surface with a mer, e.g., monomer, oligomer, polymer or the like. Suitable reactive functional sites/groups include any group that is capable of reacting with the desired monomer, oligomer or polymer. Such groups, in general, can include nucleophilic and electrophilic groups. Specific examples of such groups include carboxylic acid groups, hydroxyl groups, amino groups, epoxy groups and ester groups .

The reactive functional groups are secured to a surface upon which the polymer film is desired. Suitable surfaces for use in the process of the present invention include metal surfaces such as gold, aluminum, aluminum oxide, copper and silver, nonmetals such as glass, silicon and gallium arsenide, polymers such as polyolefins, polyesters and polyamides. In addition, combinations of the foregoing can be employed. For example, in one embodiment, a self assembled monolayer surface is provided on a suitable metal surface, e.g., gold.

The exact manner the reactive functional groups are secured to the surface is also not critical to the invention. For example, reactive sites can be a part of the material making up the surface. Alternatively, groups can be secured to the surface or even secured to an intermediate layer, e.g., which itself can be directly or indirectly secured to the surface. The key is that the reactive functional group be secured to the surface such that at least some of the reactive functional groups are accessible to the mer. Suitable means and methods of attachment would be in the purview of those skilled in the art.

As an example, one method for the attachment of suitable groups to a surface involves the use of self- assembled monolayers (SAMs) .

The formation of SAMs has been recognized in the art for a number of years as illustrated by U.S. Patent 4,539,061. Recently, one class of SAM that has received attention are organomercaptans. See, for example, Kim et al . , "Polymeric Self-Assembling Monolayers. 1. Synthesis and Characterization of w-Functionalized n- Alkanethiols Containing a Conjugated Diacetylene Group" Tetrahedron Letters, Vol. 35, No. 51., pp. 9501-9504, 1994; Kim et al . , "Polymeric Self-Assembling Monolayers. 2. Synthesis and Characterization of Self-Assembled Polydiacetylene Mono- and Multilayers." J.A .Chem.Soc. , 1995, 117, pp 3963-3967; Batchelder et al. , "Self- Assembled Monolayers Containing Polydiacetylenes" J. Am. Chem. Soc, 1994, 116, 1050-1053, each of which are incorporated by reference in their entirety.

Depending upon the oligomer or polymer ultimately employed, the reactive functional groups may be suitably activated prior to reaction with the mer. For example, in the production of hyperbranched polymer films on self- assembled monolayers, where the reactive functional groups are carboxylic acid groups, activation of such carboxylic acid groups so as to produce anhydride intermediates, acid chlorides or other active esters is preferably performed. The activated carboxylic acid groups are then reacted with the amine groups of the desired oligomer to form a surface grafted polymer. Suitable activation techniques are well within the purview of those skilled in the art and thus, need not be described in detail here. However, for sake of completeness, attention is directed to the discussion in J. March, "Advanced Organic Chemistry," 4th Ed., J. Wiley.

The reactive functional groups are reacted with a mer which provides the polymerization system with "new" reactive functional groups to replace the reactive functional group that reacted with the mer. - 7 -

Suitable " ers" which can be employed by this process include monomers, oligomers, polymers and the like. For example, suitable graft oligomer or polymer include a poly(amino acid) or derivative thereof, a polyamine, or derivative thereof, or a polycarboxylic acid or derivative thereof. In particular, where polymers are employed, those derived from a monomer with a degree of functionality greater than or equal to three are preferred. The only requirement is that the mer molecule include at least one functionality that can couple to a surface or modified surface and preferably two or more functionalities which are capable of further reaction or of being converted into a reactive functional group. As is the case with the reactive functional groups, the functionalities associated with the monomer, oligomer or polymer are not critical to the present invention as long as they are, or are capable of being converted into, a reactive functional group. Suitable examples of such functionalities include tert-butyl ester groups in poly(tert-butyl acrylate) (PTBA) , protected amines, alkenes, anhydrides, and epoxides.

The functionalities of the mer can be effectively converted into reactive functional groups by techniques which would be well within the purview of those skilled in the art. For example, in converting PTBA moieties to poly(acrylic acid) moieties, the tert-butyl ester groups can be hydrolyzed under acidic conditions and heat, e.g., 50-55 C, to form acrylic acid groups. Further, while the reactive functional groups associated with the mer molecule can be the same as the reactive functional groups already present, e.g., on the surface, they need not be the same. In fact, depending on the nature of the desired final product, the choice of different mer molecules may lead to the use of differing reactive groups. The determination of suitable reactive groups for use with various mers would also be within the purview of those skilled in the art and thus, is not described in detail here. Moreover, suitable reaction conditions for the reaction of the mer molecule with the reactive functional groups would be dependent upon the reactants employed and, as such would be determinable by those skilled in the art. For example, in the embodiment involving the production of hyperbranched polymers on SAMs, the reaction conditions are preferably compatible with the integrity of the SAM.

Subsequent to conversion of the functionalities into reactive functional groups, the foregoing steps are then repeated as needed to provide the desired polymer material. For example, with respect to the formation of hyperbranched polymers on a MUA SAM, the grafting preferably occurs at least 2 times, more preferably, 3 to 7 times depending on the desired thickness of the graft and the type of the mer used. However, this is largely based on patience and practicalities not any limitation on the chemistry.

This process is capable of providing a number of significant advantages over traditional polymerization processes. First, it can effectively compensate for insufficiencies in reaction associated with surfaces. Because there is a potential for having many grafting sites on each polymer chain, this method is capable of providing a hyperbranched polymer even if individual reactions proceed in relatively poor yield. Second, the grafted polymer films contain a high density of reactive functional groups that are suitable for further elaboration. Third, because branching occurs, to the subsequent layers contain more polymer chains, this method can lead to increasingly thicker (greater than 1000 angstroms) and more tightly packed polymer layers.

Finally, the process provides for an unusual amount of flexibility in producing a desired polymer. That is, the nature of the polymer film can be changed both during the process and derivatized subsequent to processing. This advantage can be provided while, at the same time, minimizing undesirable side reactions, e.g., chain transfer, coupling or adventitious quenching which limits the degree of polymer grafts onto the surface in additional polymerization.

In particular, the multiplication process lends itself to the production of a polymeric film having different thickness, and in fact, a polymeric film having layers of differing polymers within the film. This layer by layer approach greatly facilitates the use of the resulting polymer film in a variety of environments such as chemical sensors.

Derivatization of the resulting polymer films provides further flexibility in this regard. For example, the resulting polymer film can be derivatized in order to change interfacial properties and the like. Such derivatized films provides new platforms for chemical sensing applications and for tailoring polymer surface properties for a wide variety of technological applications.

Other examples of suitable derivatization of the polymers of the present invention includes the synthesis of fluorinated polymer films. Such films can be created by, for example, coupling an amino-terminated perfluoroalkane to layered, hyperbranched poly(acrylic acid) film. Such a feature allows for the creation of nanocomposite films with both hydrophobic, fluorinated interiors and acidic, hydrophilic exteriors. The uses for such derivatized films are potentially significant. For example, deprotonization of such films renders the surface completely hydrophilic and produces significantly reversible thickness changes.

The present invention will now be described in the terms of the following examples. These examples should be considered solely as illustrative in nature and should, in no way limit the invention described therein.

Example 1 Polymer-Grafting Procedure: Mercaptoundecanoic acid self-assembled monolayers (MUA SAMs) were prepared by immersing a plasma-cleaned gold coated slide (lOOOA Au on 50A Cr on silicon) in 0.001 M MUA in EtOH for 0.5 hour. The slide was then rinsed in EtOH and H₂0. The MUA SAM was put into a 20mL vial that contained 10 mL of dried DMF. 80/.L of N-methyl morpholine followed by 100 μL of isobutyl chlorformate was added to the vial while stirring. After 10 minutes, the slide was removed, rinsed with ethyl acetate, and blown dry with nitrogen. This slide was then placed in a solution of H₂NR-PTBA- RNH₂(200 mg in 4 mL DMF) within 20 minutes. A large excess of H₂NR-PTBA-RNH₂ (200 mg in 4 mL DMF) was employed in order to minimize crosslinking. The solution was stirred for 1 hour and the slide was then removed, rinsed with ethanol (30 mL) and dried with nitrogen. Hydrolysis of the tert-butyl ester groups was carried out by immersing the slide in a saturated benzene solution of p- toluenesulfonic acid at 50-60°C for 1 hour. The slide was then taken out, rinsed with EtOH and dried with nitrogen. Grafting of additional PTBA layers proceeded in the same manner.

Preparation of H-,NR-PTBA-RNH.,: 4' 4-Azobis (4- cyanovaleric acid) (380 mg, 1.36 mmol) , 1,4-dioxane (60 mL) and 20 mL (136 mmol) of tert-butyl acrylate were added to a flame-dried, three=necked flask under an inert atmosphere. The solution was refluxed for 20 hours. The polymer product was then precipitated from a mixture of ethanol and distilled water and dried overnight under vacuum. The product, H00CR-PTBA-RC00H (R=C (CN) CH₃) (CH₂) ₂) , was then analyzed by H and ¹³CNMR spectroscopy and was titrated with 0.01 M KOH in ethanol. A solution containing 5.0 g of the above polymer in 30 mL of CH₂C1₂ was added to a flame-dried flask under an inert atmosphere and then 324 mg of 1, 1' -carbonyldiimidazole was added under an inert atmosphere with vigorous stirring and the mixture was stirred for hours. Ethylene diamine (0.2 mL) was introduced and the stirring continued overnight. After reaction, 100 mL of CH₂C1₂ was added. The organic layer was washed (3 x 30 mL) with H₂0 and dried over anhydrous MgS0₄. The solvent was evaporated, and the product was dried overnight in vacuo to form H₂NR-PTBA-RNH₂(R=C(CN) (CH₃) (CH₂)₂C0NH(CH₂) ₂) . This final product was also analyzed by ¹H and ¹³C NMR spectroscopy and was titrated with 0.01 M HCl in an EtOH/H₂0 mixture. The Mn determined by this method was in the range of 10,000 -30,000.

Formation of a Hyperbranched Film A hyperbranched film was formed according to the synthesis method outlined in Figure 2. As illustrated by (i) and (ii) , activation of the carboxylic acid groups via a mixed anhydride followed by reaction with an α,ω-diamino-terminated poly( tert-butyl acrylate) (H₂NR-PTBA-RNH₂) yielded the grafted polymer layer, (1 of Figure 2) . Hydrolysis (p-TsOH, 50-55°C, 1 hour) then formed a grafted PAA layer, (2 of Figure 2) .

Repetition of these steps produced additional grafting at multiple sites on each prior graft leading to a layered, hyperbranched polymer film.

Each synthetic step was monitored using Fourier transform infrared external reflection spectroscopy (FTIR-ERS) . Activation of the carboxylic acid groups of the MUA monolayer (A-Figure 3) produced anhydride intermediates, which were stable enough to be observed spectroscopically at 1825 cm^"1 (B-Figure 3) . These anhydrides were then allowed to react with the amine groups of H₂NR-PTBA-RNH₂ (Mn=14, 600) to form amide bonds and hence the surface-grafted polymer. The FTIR-ERS spectrum of the grafted polymer contains a small peak at 1545 cm^"1 that we attribute to the amide bonds and a large peak at 1733 cm^"1 resulting from the ester groups of PTBA (C-Figure 3) . The tert-butyl ester group were then hydrolyzed to form a PAA graft. Peaks at 1394, 1369, 1258 and 1159 cm^"1 (D-Figure 3) due to the tert-butyl ester groups²² disappeared after hydrolysis. Changes in water contact angles from 86° to <10° and elemental analysis using X-ray photoelectron spectroscopy (XPS) confirmed that addition of the polymer and hydrolysis occurred.

Following hydrolysis of the first layer, the newly formed carboxylic acid groups were activated with isobutyl chloroformate and allowed to react with H₂NR- PTBA-RNH₂. Subsequent hydrolysis, confirmed by contact angle measurements, yielded the second grafted layer of PAA. Because each polymer chain contains several polymer grafts and each of these grafts contains additional polymer grafts, this process results in highly branched, graft polymers, Figure 4 shows FTIR-ERS spectra for films containing 1-7 grafted PTBA layers. The intensity of the C-0 peaks (1258 and 1159 cm^"1) of the tert-butyl ester, carbonyl peak (1733 cm^"1) and amide peaks (1678 & 1545 cm^"1) increased with the number of grafted layers. The nature of the polymer chains (that they are covalently grafted as opposed to just physically entangled) is confirmed by the fact that the intensity of the amide peaks increased nonlinearly. As shown in Figure 5, the ellipsometric thickness of the polymer films did not vary linearly with the number of grafted polymer layers. The thickness gained from each grafting step increased rapidly during formation of the first few layers because there were many more reactive carboxylic acid groups in each subsequent layer. This result is consistent with the trends in the intensities of the FTIR-ERS absorptions.

Figure 5 also shows the ratio of thicknesses in consecutive layers. These data suggest that a high level of branching occurs in the first few layers. in outer layers, space constraints restrict branching and layer thicknesses approach a constant value.

Example 2 Because of the large density of the functional groups, poly(acrylic acid) (PAA) films can serve as specific metal-ion binders. After exposure to an equimolar ethanolic solution Fe(Cl0₄)₃ and Ni(C10₄)₂) , the intensity of the acid carbonyl FTIR absorption (1731 cm- 1) decreased by >80% and new peaks corresponding to the symmetric and asymmetric stretches of carboxylate appeared (1582 cm^"1 and 1440 cm^"1) . These changes demonstrate metal complexation by the carboxylate receptors. In this competitive binding experiment, the films bound high levels of Fe³+ (XPS: 0/Fe=6, consistent with each Fe³⁺ coordinated to three carboxylates) , but no detectable Ni^2t. This result is in accord with the formation constants of Fe³⁺ and Ni²⁺-carboxylate complexes. To demonstrate that PAA films can be derivatized in order to change interfacial properties, the carboxylic acids on the hyperbranched polymer film (four grafted layers) were reacted with ethylene diamine. The reaction occurred after activating the COOH groups with isobutyl chloroformate as in the grafting process. The FTIR-ERS spectrum of the polymer film reveals large, newly formed amide peaks (1674,

1555 cm^"1) and a >65% decrease in the carboxylic acid carbonyl peak (1731 cm-1) .

Table 1. Ellipsometric thicknesses and contact angles (H₂0) of PTBA and PAA films as a function of the number of grafted layers.

Number Thickness³ before Contact Thickness³ of angle^b after grafted hydrolysis bafidrafter hydrolysis layers (PTBA) hydrolysis (PAA)

(A) (Degrees) (A)

MUA 14±1 <10, -- --

1 48±1 (34±2) 86, <10 30±1 (16±2)

2 144±14 (114±15) 88, <10 91+10(61 ±11)

3 330±40(240±50) 89, 25 220±20 (130±30)

4 520±60 (300±80) 88, 26 450±50(230±70)

5 840±60 (390±110) 88, 32 630±70 (180±120 )

6 1110±140 (480±210) 89, 32 1000±150 (370±2 20)

7 1510±360 (510+510) 87, 29 1340±220(340±3 70)

^a Thickness values are the average of five or more measurements on each of two samples carried through 7 layers. The values in parentheses represent the thicknesses of individual layers (total thickness minus the total thickness of the preceding hydrolyzed sample) . The water contact angles are the average of four measurements on each of two samples. The estimated error in the measurements is +2 degrees.

Example 3 Derivatization through coupling of amino- terminated perfluoroalkanes to hyperbranched PAA films was performed in two ways .

In the first method, a film containing the desired number of layers of PAA was prepared. The carboxylic acid groups throughout the film were activated and allowed to react with NH₂CH₂ (CF₂) ₇F (0.1 M in DMF) .

The second method involved grafting a mixture of H₂NR-PTBA-RNH₂ (M_n=20,100, ca 0.02 M in DMF) and NH₂CH₂ (CF₂)₇F in some or all of the layers during the synthesis of the hyperbranched polymer film.

Fluorination throughout a PAA film produced a thick, fluorinated film with a low surface energy as shown by Fourier-transform infrared external reflection spectroscopy (FTIR-ERS) , X-ray photoelectron spectroscopy (XPS) , contact angle analysis and ellipsometry. Figure 6 shows the FTIR-ERS spectra of three layers of hyperbranched PAA before and after fluorination with NH₂CH₂ (CF₂) ₇F. Upon fluorination amide peaks appeared (1680 and 1550 cm^"1) and the acid carbonyl peak (1730 cm^"1) vanished indicating that nearly all carboxylic acid groups reacted to form fluorinated amides. Figure 6 also shows the appearance of CF₂ and CF₃ stretches (1240, 1220,and 1150 cm^"1) . This highly fluorinated surface contains 45% F (XPS analysis) which represents 90% of the atomic concentration of F expected for a homopolymer of (CH₂CHCONHCH₂ (CF₂) ₇F)_n.

Figure 7 shows the XPS survey spectrum of this sample along with the high resolution C_la spectrum (inset) . There is a large C_ls peak at 291.0 eV due to CF₂ carbon and a smaller C_ls peak at 284.6 eV due to CH_X - 16 - carbon, again showing the extensive grafting. Essentially all of the accessible carboxylic acid groups inside or at the surface of the film reacted with NH₂CH₂ (CF₂) ₇F and are unavailable for further grafting. Fluorination of a hyperbranched PAA film also changed the film thickness. On a sample containing three layers of PAA grafting of NH₂CH₂ (CF₂)₇F doubled the ellipsometric thickness to about lOOOA. Such a large increase in thickness shows that grafting must be taking place throughout the film because the height of a single monolayer of NH₂CH₂ (CF₂) ₇F would only be about IOA. The total film thickness can be varied easily by changing the number of PAA layers in the film.

Contact angle measurements show that grafting of NH₂CH₂ (CF₂) ₇F lowers surface energy. The contact angle for a sample composed of 3 layers of PAA changed from 30° to 107° upon fluorination. By comparison, grafting a layer of pure NH₂CH₂ (CF₂) ₇F onto a MUA monolayer increased the contact angle from <10° to 113°. Example 4

In addition to forming fully fluorinated films, nanocomposite materials which possess fluorinated interiors were also produced. A mixed grafting of NH₂CH₂ (CF₂) ₇F and NH₂R-PTBA-RNH₂ (Scheme 1) was employed to create a small but sufficient number of PAA sites for subsequent grafting. A of Figure 8 shows the FTIR-ERS spectrum of a sample containing two layers of PAA on which we grafted a mixture of NH₂CH₂ (CF₂) ₇F and NH₂R-PTBA- RNH₂ (30:1 molar ratio in the grafting solution) . The C- F_x stretching modes (1240, 1220, and 1150 cm^"1) confirm fluorination. B of Figure 3 shows the spectrum of this sample after grafting an additional layer of pure PAA. This spectrum confirms additional grafting of PAA (the carbonyl peak increases) and the retention of the fluorinated layer (the C-F_x stretches are still present) . The top layer of pure PAA fully attenuated the F XPS signal indicating that the fluorinated layer was indeed covered with a PAA layer. The FTIR-ERS and XPS data demonstrate the formation of a nanocomposite with a fluorinated interior.

Example 5 A hydrophilic surface on a hydrophobic fluorinated interior was also created. In this regard, a layer of NH₂CH₂ (CF₂) ₇F and PAA (500:1 ratio in the grafting solution) was grafted directly onto MUA. In this case, the film surface was very hydrophobic (θa = 100°) . No change in hydrophobicity occurred after exposure to a 0.1 M NaOH solution (θa = 99°) . After grafting two additional layers of pure PAA onto this mixed layer, the surface became hydrophilic (θa = 14°) and was completely wet after exposure to 0.1 M NaOH. Thus a very hydrophobic fluorine-containing film was made very hydrophilic simply by covalently capping this layer with pure PAA layers. Although the present invention has been described in terms of certain preferred embodiments, those skilled in the art would recognize that various modifications, substitutions, omissions and other changes could be made without departing from the spirit thereof. Accordingly, the scope of the present invention should be limited only by the scope of the following claims including equivalents thereof.

Claims

What is claimed is:

1. A method of forming a graft polymer comprising: reacting an oligomer or polymer with a reactive surface or reactive functional group attached to a surface; said oligomer or polymer being capable of providing two or more reactive functional groups for subsequent reaction with additional molecules, and repeating the foregoing step one or more times so as to form a graft polymer on the surface.

2. The method according to claim 1 wherein the monomer, oligomer or polymer include two or more functionalities which are converted to reactive functional groups after the molecules are reacted with a reactive surface or reactive functional group.

3. A method of multiplication polymerization comprising:

(a) providing a surface including reactive functional groups or reactive sites; (b) reacting one or more of the reactive functional group or reactive site with a monomer, oligomer or polymer so as form a covalent bond therewith, with the monomer, oligomer or polymer being capable of providing two or more additional reactive functional groups for subsequent reaction with a monomer, oligomer or polymer; and

(c) repeating (a) and (b) one or more times.

4. The method according to claim 3 wherein the monomer, oligomer or polymer include two or more functionalities which are converted to reactive functional groups after the molecules are reacted with a reactive site or reactive functional group.

5. A method of multiplication polymerization capable of forming a highly branched polymer on a surface comprising:

(a) providing a surface containing reactive functional groups or reactive sites;

(b) reacting at least one reactive functional group or reactive sites with a monomer, oligomer or polymer which includes a plurality of functionalities capable of forming additional reactive functional groups;

(c) converting one or more of the functionalities to provide additional reactive functional groups; and

(d) repeating (b) and (c) one or more times to provide a polymer film.

6. The method according to claim 5 wherein the reactive functional groups involved in hyperbranching are carboxylic acid groups, hydroxyl groups, amino groups, epoxy groups or ester groups.

7. The method according to claim 5 wherein the functionalities are derived from acrylic acid groups.

8. The method according to claim 5 wherein the graft oligomer or polymer comprises a poly(amino acid) or derivative thereof, a polyamine, or derivative thereof, or a polycarboxylic acid or derivative thereof.

9. The method according to claim 5 wherein the polymer is derived from a monomer with a degree of functionality greater than or equal to three.

10. A method according to claim 5 wherein at least two different oligomer or polymers are sequentially employed to provide a polymer film having at least two layers.

11. A method according to claim 5 wherein the polymer film is derivatized so as to modify an interfacial property of the polymer film.

12. The method according to claim 11 wherein the polymer film comprises poly(acrylic acid) and derivatization comprises coupling amino-terminated perfluoroalkanes to acrylic acid moieties of the polymer film.

13. The method according to claim 5 wherein the polymer film is a hyperbranched polymer film.

14. A method of forming a graft polymer film on a self-assembled monolayer comprising:

(a) providing a self-assembled monolayer on a substrate, said self-assembled monolayer having reactive functional groups on the surface thereof, (b) reacting the functional groups with a diamino-terminated poly( ert-butyl acrylate) to provide a grafted polymer layer;

(c) hydrolyze the grafted polymer layer so as to provide a grafted layer comprising poly(acrylic acid) ; (d) activation of the carboxylic acid groups for formation of an amide bond; and

(e) repeat (b) - (d) one or more times to provide a polymer film.

15. The method according to claim 14 wherein said self-assembled monolayer is formed form a mercaptonundecanoic acid on the surface thereof; and where the process further comprises, between (a) and (b) : activating the acid groups of the mercaptonundecanoic acid to form a mixed anhydride or an active ester.

16. The method according to claim 14 wherein the substrate comprises gold, aluminum, aluminum oxide, copper, silver, glass, silicon, gallium arsinide, or a reactive polyolefin, polyester, or polyamide.

17. The method according to claim 14 wherein the polymer film is a hyperbranched polymer.