Anionic Grafting onto Divinylbenzene-Cross-Linked Polystyrene

Anionic grafting onto divinylbenzene (DVB)-cross-linked polystyrene is described. Using commercially available chloromethylated DVB-cross-linked polys...
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Anionic Grafting onto Divinylbenzene-Cross-Linked Polystyrene D. E. Bergbreiter* and Zhenqi Zhong Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012

Anionic grafting onto divinylbenzene (DVB)-cross-linked polystyrene is described. Using commercially available chloromethylated DVB-cross-linked polystyrene, a lithiated diarylmethyl derivative was prepared by a substitution of the chloromethyl chloride group by phenyllithium, which was followed by an in situ deprotonation by excess phenyllithium. Protonation of this resin led to a neutral phenylmethyl derivative of the original polystyrene that could be deprotonated by n-butyllithium, sec-butyllithium, phenyllithium, or sodium naphthalenide to form an anionic resin that in turn reacts readily with monomers like tert-butyl acrylate or 4-vinylpyridine to form anionically grafted products. Quantitative conversion of the tert-butyl acrylate grafts into poly(acrylic acid) grafts via acidolysis and the application of these poly(acrylic acid) grafts as a precursor for a Pd(0) hydrogenation catalyst is also described. Modification of insoluble cross-linked polystyrene resins is of historical and current importance. These materials are the basis of many of the commonly used ion exchange supports and are the most common sort of support used in biotechnology, combinatorial and high-throughput chemistry for synthesis.1-5 Modification of these common cross-linked polymers can be accomplished in various ways. The unfunctionalized insoluble polymer itself is available in various forms with varying extents of DVB-cross-linking and solvent swellabilitysparameters that often dictate the ultimate utility of resin supports that are further modified for synthesis. The nature of the cross-linking group itself can usefully be varied.6-8 However, the most important modifications usually are those that introduce functional groups onto the polymer. Most often this involves an electrophilic substitution followed by subsequent modification of the functional group on the resin.2 A less common approach has involved the introduction of graft copolymers onto cross-linked polystyrene. Such grafts can facilitate synthesis either by modification of the intraresin environment or by incorporation of additional functionality.9-13 Poly(alkene oxide) grafts are among the most common sorts of grafts. However, radical grafting too has been used to modify polystyrene supports to make them more useful in synthesis. In this report, we describe an alternative procedure that employs a readily available organolithium derivative of the most commonly available version of Merrifield resin (chloromethylated DVB-cross-linked polystyrene) to introduce polyester, poly(vinylpyridine), and poly(acrylic acid) grafts onto these supports. The preparation of synthetically useful solid alkalimetal derivatives of polymers or inorganic materials has been described.14-16 In this report, we used a very simple and convenient method we had developed earlier for formation of alkali-metal derivatives of commercially available DVB-cross-linked polystyrenes.17 This method involves the in situ generation and deprotonation of a polymeric analogue of diphenylmethane derived from commercially available 1% or 2% divinylbenzene crosslinked chloromethylated polystyrene (Merrifield resin), which reacts readily with excess phenyllithium in * To whom correspondence should be addressed. E-mail: [email protected].

ether-THF suspensions to form poly(styrylphenylmethyl)lithium (1) (eq 1). While this reactive polymer can be stored under appropriate water- and oxygen-free conditions, its water- and oxygen-sensitivity we led us to treat this polymer with methanol to form the neutral polystyrene-bound diphenylmethane analogue 2. Reaction of polymer 2 with any organolithium reagent (e.g commercially available n-butyllithium) could then regenerate 1 as needed (eq 2). Deprotonation of 2 with other strong bases (e.g., sodium naphthalene) could also be used to form other alkali metal derivatives of 2 (eq 3). In these deprotonation experiments, the polymers 1 or 3 were washed with THF prior to grafting to remove any soluble base. This ensured the any species that were used as initiator groups in subsequent grafting chemistry were immobilized on the beads.

Alkali-metal derivatives of 2 like 1 or 3 are highly colored insoluble solids (beads) whose rapid reaction with oxygen or protic species such as water or alcohols is visible by a rapid loss of color of the polymeric analogue of diphenylmethyllithium. This reactivity of 1 parallels the reactivity of low molecular weight diphenylmethyllithium and led us to expect that 1 would be a useful precursor for anionic grafting chemistry just as diphenylmethyllithium is useful in solutionstate anionic polymerization.18,19 Success in anionic grafting was first demonstrated by the reaction of 1 with tert-butyl acrylate (t-BA) to form polystyrene-grafted-poly(tert-butyl acrylate) (PS-g-Pt-BA 4) (eq 4). Gravimetric analysis of the grafted PS-g-PtBA resins prepared in different experiments with varying graft conditions showed that the extent of grafting did not vary much with conditions. Doubling the ratio of t-BA to 2 or changing reaction times at room tem-

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Ind. Eng. Chem. Res., Vol. 44, No. 23, 2005 8617 Table 1. Anionic Graft Polymerization of tert-Butyl Acrylate onto a Lithiated Polystyrenea procedure PS-diphenylmethane 2 (g) tert-butyl acrylate (mmol) reaction time (d) PS-g-Pt-BA product (g) loading of t-BA (mmol/g)

A 10.0 102 6 40.2 5.9

B 10.0 99 14 40.5 5.9

C 10.0 81 14 35.4 5.6

D 10.0 69 3 31.4 5.3

E 10.0 65 3 27.1 4.9

could also be grafted onto phenylmethylated DVB-crosslinked polystyrene. For example, 4.8 mmol of 4-vinylpyridine could be grafted onto this phenylated resin using the reaction shown in eq 6 based on gravimetric analysis.

a All the reactions used 10 g of 2 (10 mmol), 20 mL (32 mmol) of 1.6 N BuLi to generate the anionic polymer 1, and 400 mL of THF as the solvent for the graft polymerization that was carried out at room temperature.

perature from 3 to 14 d produced roughly the same loadings of grafted tert-butyl acrylate. These loadings ranged from 4.9 to 5.9 mmol of t-BA/g of resin. We did not ascertain if the lack of change in loading in reactions that spanned a 3-14 d time period is a steric issue or if the graft polymerization was not living past the point where loadings reached 5-6 mmol of t-BA/g since this level of loading is already close to the 7.8 mmol of ester groups/g that would obtain for pure tert-butyl acrylate. No detectable amount of soluble poly(tert-butyl acrylate) was formed in these grafting experiments, presumably because the enolate intermediates in these anionic grafting reactions unlike radical intermediates in radical grafting chemistry do not undergo chain transfer reactions with solvent or monomer. Representative results for the extent of grafting onto a functional polystyrene resin in several multigram grafting experiments are listed in Table 1.

Polystyrene-g-poly(tert-butyl acrylate) (PS-g-Pt-BA, 4) was also useful as a precursor for a poly(acrylic acid) graft since the tert-butyl ester group undergoes ready acidolysis with strong acids (eq 5). In a typical example, a 20 g sample of a PS-g-Pt-BA grafted resin that contained 5.6 mmol of t-BA/g of resin was treated with methanesulfonic acid to form 13.9 g of polystyrene-gpoly(acrylic acid) (PS-g-PAA). The weight loss and the titrimetrically measured loading of poly(acrylic acid) on the product PS-g-PAA confirmed the original analysis of the poly(tert-butyl acrylate) loading.

The PS-g-PAA formed in this acidolysis reaction behaved like other poly(acrylic acid) grafts in that the -CO2H groups could be quantitatively converted into sodium carboxylates by treatment with NaOH in water. This deprotonation and a subsequent protonation was completely reversible and quantitative based on the disappearance/reappearance of the -CO2H group at 1700 cm-1 on deprotonation/protonation. In addition to poly(tert-butyl acrylate), other monomers that can be polymerized by anionic polymerization

Swelling is an important characteristic of resins used in synthesis or catalysis.20-22 Our earlier work leading to the lithiated polymer 1 had indicated that the initial lithiation chemistry produced some lithiated sites that were not regenerable after protonation. We had earlier suggested that this low concentration of unregenerable basic sites arose from cross-linking of chloromethylphenyl anions on the resin.17 The anionically grafted resins described here should also contain this extra crosslinking and we expected this extra cross-linking would affect the product resin’s solvent dependent swellability. A comparison of the swelling ratios of the poly(tert-butyl acrylate) and poly(sodium acrylate) grafted polystyrene resins with reported swelling values for chloromethylated polystyrene and other functionalized polystyrene resins used in synthesis in 12 solvents at room temperature are listed in Table 2.23 While other substituted insoluble polystyrenes with polar groups have solvent dependent swelling, the PS-g-t-BA, PS-g-PAA, and PSg-PAA-Na prepared by these anionic grafting reactions had relatively small differences in swelling ratio for various solvents. While the Na salt derivative did swell more in polar solvents than in other solvents, the changes were not large. This result is in accord with the notion that some of the aforementioned cross-linking occurred during the lithiation step. These data show that PS-g-P(t-BA) and PS-g-PAA had moderate swelling ratios in a range of solvents. The data vary in a predictable way relative to the starting diphenylmethylated and chloromethylated DVB-crosslinked polystyrene resins. The sodium salt of PS-g-PAA, PS-g-PAA-Na (6), had a swelling ratio that was largely invariant to solvent though it did swell to ca. 50% more in the most polar solvent, water. Reported swelling data for DVB-cross-linked polystyrene were similar to the data we measured for the starting Merrifield resin. Data for other grafted resins showed they generally had more solvent dependent swellability that the anionically grafted resins prepared in our work. The work described above shows that grafted functionalized polystyrene with high loadings of poly(acrylic acid) is accessible by anionic polymerization from commercial chloromethylated resin. Preliminary work using metal sorption, reduction and catalysis shows that these resins can also serve as precursors of polymer-supported catalysts. In this work, we exchanged Pd(II) with the carboxylic acid salt of a PS-g-PAA-Na resin (eq 7). While this exchange process did not convert all the -CO2H groups of the poly(acrylic acid) graft into palladium salts, reduction of these Pd salts with H2 in EtOH did successfully produce a black resin supported Pd catalystsPS-g-PAA-Pd(0) (eq 7). Digestion and Pd analysis of the product resin showed that this process led to catalysts containing 1.1 mg atom of Pd/g of resin.

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Table 2. Comparative Solvent Swelling Studies of Grafted Cross-Linked Polystyrene Derivatives in Various Solvents resina

Merrifield PS-CHPh2b PS-g-t-BAc PS-g-PAAd PS-g-PAA-Nae polystyrene (1% DVB)f Hypogel 400f Tentagel Sf Tentagel HLf

H2O

MeOH

EtOH

CH2Cl2

PhMe

DMF

MeCN

THF

Et2O

1.02 1.02 1.09 1.48 1.65

1.05 1.37 1.15 2.05 1.32 1.00 1.71 2.12 2.12

1.07 1.17 1.31 1.90 1.20 1.05 1.65 1.71 2.06

4.16 2.39 1.64 1.33 1.20 5.19 4.06 3.71 3.35

4.20 2.45 1.65 1.10 1.10 5.31 3.24 2.82 2.41

3.15 1.84 1.42 2.33 1.10 3.50 3.06 2.76 2.71

1.30 1.18 1.28 1.24 1.15 2.00 2.71 2.47 2.29

4.60 2.51 1.63 1.67 1.15 5.50 3.12 2.94 2.47

2.06 1.56 1.35 1.23 1.15 2.50 1.53 1.12 1.41

1.06 2.12 1.82

a The Merrifield resin had a loading of 1.05 mmol of Cl/g and 1% DVB cross-linking and was the chloromethylated resin that served as a precursor to the tert-butyl acrylate and acrylic acid grafted materials. b The polystyryldiphenylmethyl resin had a loading of diphenylmethyl groups of 1 mmol of Ph2CH-/g of resin. c The PS-g-Pt-BA has a loading of 5.3 mmol of t-BA/g. d The PS-g-PAA had a loading of 8.0 mmol of -CO2H/g. e The PS-g-PAA-Na had a loading of 6.7 mmol of -CO2Na/g. f These data were obtained from product listings on the Internet (cf. http://www.rapp-polymere.com/preise/tent_s_d.htm#swelling) and are ratios of swelling of the polymeric support in the solvent listed relative to the volume of the polymer support in the absence of solvent.

Table 3. Hydrogenation Reactions Using PS-g-PAA-Pd(0) (7) and Various Alkenesa alkene

yieldb

cyclohexene 1-decene 1-decyne 10-undecenylic acid 4-allylanisole cinnamic acid diphenylethyne 4-acetoxystyrene

100b 100b,c 100b 100b,d 100b 95e 97b 99e

a The hydrogenation reactions were carried out at room temperature using 2 mol % of catalyst 7 in THF. Reaction times varied but reactions were typically complete in 8 h or less. b These are yields based on a GC analysis. c GC analysis before the reaction was complete indicated that some isomerization occurred for terminal alkenes. d A GC analysis of a competitive reaction of 1-decene and 10-undecylenic acid showed little or no chemioselectivity for these two different substrates. e These are yields of isolated reduced product.

These polystyrene-grafted poly(acrylic acid) supported Pd(0) species proved to be similar to conventional Pd(0) hydrogenation catalysts. Representative data for alkene hydrogenations with a range of substrates are shown in Table 3. While the PS-g-PAA-encapsulated catalyst was not remarkably more or less reactive than other Pd catalysts in polystyrene resin beads or Pd catalysts immobilized in polyacid grafts on other supports,24-29 the capacity of these Pd(0) supported catalysts for hydrogenation of the range of structurally diverse alkene substrates shows that these anionically grafted resins have the potential to be usefully modified to make other polymer-supported reagents and catalysts.

Figure 1. Kinetics for hydrogenation of cinnamic acid: 2 mol % of Pd/C in EtOH (b) (1 mmol scale reaction); 2 mol % of PS-gPAA-Pd(0) in EtOH (O) (1 mmol scale reaction); 5 mol % of PSg-PAA-Pd(0): in THF suspension in a first (9), second (gray box), or third (0) cycle on a 2 mmol scale.

styrene though the isolated yield of 4-acetoxyethane in a 4 h room-temperature reduction of this substrate in EtOH was excellent (99%). In the case of diphenylethyne, 2 mol % of the PS-g-PAA-Pd(0) catalyst 8 afforded a 97% yield of bibenzyl after 70 min in a hydrogenation in acetone. During this period, GC analysis showed that the maximum yield of stilbene was 5 mmol of functional groups/g of resin are easily obtained. The product resins are intermediate in their solvent-dependent swellability relative to other grafted resins. The poly(tert-butyl acrylate) grafts on these polystyrenes can be modified using conventional acidolysis chemistry to prepare highly loaded poly(acrylic acid) grafted resins that in turn can be used as precursors of heterogeneous Pd(0) catalysts. Extensions of this chemistry to other monomers, further derivatization of the intermediate poly(acrylic acid) grafts and further

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studies of the Pd catalysts in other Pd-catalyzed reactions are ongoing and will be reported in due course. Experimental Section General Methods. Merrifield resin (RGEN100) was obtained from American Peptide Company, Inc., as a 100-200 mesh resin and had a loading of 1.05 mmol of ClCH2- groups/g. Other reagents and solvents were obtained from the Aldrich Chemical Co. and used as received unless noted otherwise as described below. THF was dried by first distilling it from sodium benzophenone. Before use in reactions, it was further purified by five freeze-thaw cycles using vacuum and Ar. tert-Butyl acrylate was washed with aqueous NaOH (0.1 N) three times (50 mL) to remove inhibitors, then washed with distilled water, and finally dried with CaCl2. It was then distilled under reduced pressure in an all-glass apparatus. The middle fraction was collected, dried with 4 Å molecular sieve and freed from O2 by five freeze thaw cycles using vacuum and Ar. 4-Vinylpyridine was purified before use by distillation. Preparation of Poly(styrylphenylmethane) (2).17 In a typical procedure, 40 g of chloromethylated polystyrene (1.05 mmol of Cl/g) was placed in a 500 mL flame-dried, round-bottomed flask which was filled with N2. THF (300 mL) was added to this polymer to give a slurry of the solvent swollen polymer, which then was cooled to -78 °C. Addition of 100 mL of freshly prepared 1.0 M phenyllithium in ether produced a blackish resin that was allowed to shake for 26 h. Addition of 100 mL of CH3OH to this slurry of lithiated polymer in THF produced polymer 2 which was filtered, washed with THF (150 mL 4 times), and extracted for 18 h in a Soxhlet extraction apparatus with hot THF. After drying, 2 was obtained as light yellow polymer beads. Anionic Graft Polymerization. In a typical procedure, 10.0 g of poly(styrylphenylmethane) (2) was added to a 1-L flame-dried round-bottomed flask which was filled with N2 or Ar. THF (40 mL) was added to this polymer to give a slurry of the solvent swollen polymer which was then cooled to -78 °C. Addition of 20 mL of 1.6 M butyllithium in hexanes followed by shaking 3 h at room temperature produced a suspension of black resin beads. The supernatant solvent was transferred from this flask by forced siphon using a cannula and the resin beads were washed with THF three times with 30 mL portions of THF to remove any soluble base. Analysis of the last wash with aqueous phenolphthalein showed the last wash contained no base. At this point, the resin beads were still black. Then THF (400 mL) was added to the flask at room temperature using a cannula. The subsequent addition of 150 mL of tertbutyl acrylate led to an immediate color change of the resin beads from black to light yellow. The reaction mixture was then allowed to agitate on a wrist action shaker for 3 d at room temperature. The product was isolated by filtration after addition of 100 mL of CH3OH. Washing first with THF (3 × 100 mL), EtOH (3 × 100 mL), and finally acetone (3 × 100 mL) yielded (after air-drying) 40.1 g of PS-g-P(t-BA) 3 in the form of white beads. Acidolysis of PS-g-P(t-BA) (3). A 20.0 g sample of 3 was placed in a 300 mL round-bottomed flask. After addition of 150 mL of CH2Cl2 and 20 mL of MeSO3H, the resulting suspension was allowed to shake on a wrist action shaker at room temperature for 3 h. Filtration and washing first with water (3 × 50 mL),

EtOH (3 × 50 mL) and acetone (3 × 50 mL) was followed by drying in a vacuum for 48 h to yield 13.9 g of the product resin. The weight loss of 6.1 g corresponded to 109 mmol of isobutylene which gravimetrically corresponded to 7.84 mmol of product -CO2H groups/g of resin. This value agreed with a titrimetric analysis of the -CO2H loading. In this titrimetric analysis, a 0.2 g sample of this resin was allowed to react with an excess (0.1925 g) of NaOH in 20 mL of H2O. The supernatant aqueous base solution was then titrated to a phenolphthalein end point with 0.1 N HCl. This titration indicated that the 0.2 g sample of PS-g-PAA contained 1.54 mmol of -CO2H groups corresponding to a loading of 7.7 mmol of -CO2H groups/g. Sodium Salt Synthesis. A 5.0 g sample of the PSg-PAA resin was suspended in 100 mL of EtOH that contained 2.5 g of NaOH. After shaking on a wrist action shaker for 24 h at room temperature, the product resin was recovered by filtration and washed with three 50 mL portions of water and three 50 mL portions of EtOH to yield 6.05 g of PS-g-PAA-Na (6). Pd Catalyst Synthesis. A 5.0 g sample of the PSg-PAA-Na resin was suspended in a mixture 100 mL of acetone and 50 mL of water containing 8.98 g of palladium acetate and allowed to shake for 24 h at room temperature. Then the excess solution was removed and the product resin was washed with five 100 mL portions of water and three 100 mL portions of acetone and airdried to yield 5.78 g of dark brown peaks. Analysis of Pd Loading in PS-g-Pd Catalyst by Inductively Coupled Plasma Atomic Spectroscopy. Analysis of the Pd loading of the PS-g-PAA-Pd(0) catalyst was carried out according to a literature procedure.30 A sample of the PS-g-PAA-Pd(0) (0.20 g) was placed in a 20 mL quartz crucible. Combustion (1.5 h) in a furnace produced 38.1 mg of a black residue. This residue was then completely dissolved with heating using 5 mL of aqua regia (concentrated HCl:HNO3 ) 3:1) and 5 mL of fuming HNO3. The resulting solution was diluted to 25 mL using 10% HNO3 in a volumetric flask. A portion (1 mL) of this solution was diluted to 100 mL and this dilute solution was analyzed by inductively coupled plasma atomic emission spectroscopy. These results were calibrated with standard solutions that contained 10, 8, 6, 4, 2, and 1 ppm of Pd(II). The average analysis result for three separate analyses of the same PS-g-PAA-Pd(0) sample was 9.5 ppm - a value that corresponds to a loading of ca. 1.11 mg atom of Pd/g of PS-g-PAA-Pd(0) ((25 × 100 × 9.47 × 10-6/0.2) ) 0.118 g of Pd/g of PS-g-PAA-Pd(0)). A blank solution prepared using 0.20 g of PS-g-PAA as the “Pd” source was also prepared and had no detectable Pd. Hydrogenation Experiments. Hydrogenation experiments were typically performed using 2 mol % of the PS-g-PAA-Pd(0) catalyst using a flame-dried, 50 mL, round-bottomed flask with a sidearm. For the Pd catalyst that had a loading of 0.118 g of Pd/g of PS-gPAA-Pd(0) (a loading of 1.1 mg atom of Pd/g of resin), this corresponds to 18 mg of the polymeric catalyst/ mmol of substrate. Hydrogenations were also successful with lower (0.5 mol %) catalyst loadings. Solvents like THF or EtOH were used in the hydrogenation reactions. In kinetic studies, the flask with the catalyst suspended in solvent was attached to a gas buret containing H2 and then evacuated and filled with H2 3 times. The reaction mixture solution (10 mL) was added with a

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syringe. In kinetic studies, the volume of H2 uptake was recorded at convenient intervals and the data were plotted as time vs the consumed volume of H2 (mL). The PS-g-PAA-Pd(0) catalyst could also be used at higher pressure (40 psi) in a Paar apparatus and this procedure was used in 10 mmol scale hydrogenations of 4-acetoxystyrene and cinnamic acid. Products in those cases were isolated and characterized by NMR spectroscopy. In smaller scale or synthetic reactions, progress of reactions and yields were determined by gas chromatography using internal standards. Comparisons of synthetic reactions or of kinetic results with commercial 10% Pd/C used the same apparatus and the same reaction conditions. Swelling Studies. In these studies, a 0.2 g sample of resin was placed in an NMR tube. The height of the resin column was measured. Then a series of solvents were added to the resin. After 24 h at room temperature, the height of the wet resin was measured and the ratio of the height of the wet swollen resin to the original height is the swelling ratio listed in Table 2. Acknowledgment Support of this work by the National Science Foundation and by the Robert A. Welch Foundation is gratefully acknowledged. Literature Cited (1) McNamara, C. A.; Dixon, M. J.; Bradley, M. Recoverable Catalysts and Reagents Using Recyclable Polystyrene-Based Supports. Chem. Rev. 2002, 102, 3275-3299. (2) Guillier, F.; Orain, D.; Bradley, M. Linkers and Cleavage Strategies in Solid-Phase Organic Synthesis and Combinatorial Chemistry. Chem. Rev. 2000, 100, 2091-2157. (3) Shuttleworth, S. J.; Allin, S. M.; Sharma, P. K. Functionalized polymers. Recent developments and new applications in synthetic organic chemistry. Synthesis 1997, 1217-1239. (4) Shuttleworth, S. J.; Allin, S. M.; Wilson, R. D.; Nasturica, D. Functionalized polymers in organic chemistry; Part 2. Synthesis 2000, 8, 1035-1074. (5) Alexandratos, S. D.; Crick, D. W. Polymer-Supported Reagents: Application to Separation Science. Ind. Eng. Chem. Res. 1996, 35, 635-644. (6) Roice, M.; Kumar, K. S.; Pillai, V. N. R. Synthesis, Characterization, and Application of Butanediol Dimethacrylate CrossLinked Polystyrene: A Flexible Support for Gel Phase Peptide Synthesis. Macromolecules 1999, 32, 8807-8815. (7) Toy, P. H.; Reger, T. S.; Janda, K. D. Tailoring polystyrene solid-phase synthesis resins: incorporation of flexible cross-linkers. Aldrichimica Acta 2000, 33, 87-93. (8) Rana S, White P, Bradley M, J. Influence of resin crosslinking on solid-phase chemistry. J. Comb. Chem. 2001, 3, 9-15. (9) Hodges, J. C.; Harikrishnan, L. S.; Ault-Justus, S. Preparation of Designer Resins via Living Free Radical Polymerization of Functional Monomers on Solid Support. J. Comb. Chem. 2000, 2, 80-88. (10) Wisnoski, D. D.; Leister, W. H.; Strauss, K. A.; Zhao, Z.; Lindsley, C. W. Microwave-initiated living free radical polymerization: rapid formation of custom Rasta resins. Tetrahedron Lett. 2003, 44, 4321-4325. (11) Gooding, O. W.; Baudart, S.; Deegan, T. L.; Heisler, K.; Labadie, J. W.; Newcomb, W. S.; Porco, J. A., Jr.; Van Eikeren, P. On the Development of New Poly(styrene-oxyethylene) Graft

Copolymer Resin Supports for Solid-Phase Organic Synthesis. J. Comb. Chem. 1999, 1, 113-122. (12) Rapp, W. PEG grafted polystyrene tentacle polymers: physicochemical properties and application in chemical synthesis. Comb. Pept. Nonpept. Libr. 1996, 425-464. (13) Larpent, C.; Amigoni-Gerbier, S.; De Sousa, D.; A.-P. Synthesis of metal-complexing nanoparticles by post-functionalization of reactive nanolatexes produced by microemulsion polymerization. C. R. Chim. 2003, 6, 1275-1283. (14) Bergbreiter, D. E.; Killough, J. M. Reactions of potassiumgraphite. J. Am. Chem. Soc. 1978, 100, 2126-2134. (15) Bergbreiter, D. E.; Killough, J. M.; Parsons, G. L. Polymeric organometallics as precursors of polymer-supported catalysts. In Fundamental Research in Homogeneous Catalysis, Tsutsui, M., Ed.; Plenum: New York, 1979; pp 651-657. (16) Bergbreiter, D. E.; Killough, J. M. Polymer-bound alkali metal aromatic radical anions. Chem. Commun. 1980, 319-320. (17) Bergbreiter, D. E.; Blanton, J. R.; Chen, B. Polystyrenebound analogues of alkali metal diphenylmethyl anions. J..Org. Chem. 1983, 48, 5366-5368. (18) Baskaran, D. Strategic developments in living anionic polymerization of alkyl (meth)acrylates. Prog. Polym. Sci. 2003, 28, 521-581. (19) Jagur-Grodzinski, J. Functional polymers by living anionic polymerization. J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2116-2133. (20) Vaino, A. R.; Goodin, D. B.; Janda, K. D. Investigating resins for solid-phase organic synthesis: the relationship between swelling and microenvironment as probed by EPR and fluorescence spectroscopy. J. Comb. Chem. 2000, 2, 330-336. (21) Gambs, C.; Dickerson, T. J.; Mahajan, S.; Pasternack, L. B.; Janda, K. D. High-Resolution Diffusion-Ordered Spectroscopy To Probe the Microenvironment of JandaJel and Merrifield Resins. J. Org. Chem. 2003, 68, 3673-3678. (22) Wang, Z.; Luo, J.; Zhu, X. X.; Jin, S.; Tomaszewski, M. J. Functionalized Cross-Linked Poly(vinyl alcohol) Resins as Reaction Scavengers and as Supports for Solid-Phase Organic Synthesis. J. Comb. Chem. 2004, 6, 961-966. (23) Swelling data for commercially available resins in Table 2 were obtained from product data listed on the Internet (cf. http:// www.rapp-polymere.com/preise/tent_s_d.htm#swelling). (24) Bergbreiter, D. E.; Chen, B.; Lynch, T. J. Palladium/ polystyrene catalysts. J. Org. Chem. 1983, 48, 4179-4186. (25) Bergbreiter, D. E.; Chen, B.; Weatherford, D. New strategies in using macromolecular catalysts in organic synthesis. J. Mol. Catal. 1992, 74, 409-419. (26) Bergbreiter, D. E.; Kippenberger, A. M.; Tao, G. Functionalized hyperbranched grafts on polyethylene powder for support of Pd(0)-phosphine catalyst. Chem. Commun. 2002, 2158-2159. (27) Kidambi, S.; Dai, J.; Li, J.; Bruening, M. L. Selective Hydrogenation by Pd Nanoparticles Embedded in Polyelectrolyte Multilayers. J. Am. Chem. Soc. 2004, 126, 2658-2659. (28) Kidambi, S.; Bruening, M. L. Multilayered Polyelectrolyte Films Containing Palladium Nanoparticles: Synthesis, Characterization, and Application in Selective Hydrogenation. Chem. Mater. 2005, 17, 301-307. (29) Coleman, D. R.; Royer, G. P. New hydrogenation catalyst: palladium-poly(ethylenimine) “ghosts”. Applications in peptide synthesis. J. Org. Chem. 1980, 45, 2268-2269. (30) Bergbreiter, D. E.; Chandran, R. Polyethylene-bound rhodium(I) hydrogenation catalysts. J. Am. Chem. Soc. 1987, 109, 174179.

Received for review January 29, 2005 Revised manuscript received March 24, 2005 Accepted March 28, 2005 IE050116+