Hydrosilylation grafting

Chen et al. utUized a direct chemical reaction with a given solution (wet treatment) to modify the surface of the silicone rubber. The presence of a layer of PEO on a biomaterial surface is accompanied by reductions in protein adsorption, and cell and bacterial adhesion. In order to obtain a PEO layer on top of the silicone rabber surface, the surface was firstly modihed by incorporating an Si-H bond using (MeHSiO) , and followed by PEO grafting to the surface using a platinum-catalyzed hydrosilylation reaction. These PEO-modified surfaces were demonstrated by fibrinogen adsorption both from buffer and plasma, as well as albumin adsorption from buffer. Reductions in protein adsorption of as much as 90% were noted on these surfaces. 

The synthesis and characterization of a series of dendrigraft polymers based on polybutadiene segments was reported by Hempenius et al. [15], The synthesis begins with a linear-poly(butadiene) (PB) core obtained by the sec-butyllithium-initiated anionic polymerization of 1,3-butadiene in n-hexane, to give a microstructure containing approximately 6% 1,2-units (Scheme 3). The pendant vinyl moities are converted into electrophilic grafting sites by hydrosilylation with... 

The simultaneous hydrosilylation and ring-opening polymerization process provides a powerful method for the construction of a variety of novel polymer networks including comb, block and graft polymers, e.g. 272 (equation 102)271. 

Hydrosilylation was also applied to the preparation of thiophene-terminated dimethyl-siloxane macromonomer, which is used for the synthesis of thiophene-dimethylsiloxane graft copolymers by oxidative polymerization281. Polycarbosilanes have been prepared by hydrosilylation-polymerization of l,4-bis(ethenylmethylphenylsilyl)benzene with 1,4-bis(methylphenylsilyl)benzene in various ratios282. 

Chemical modifications of copoly[methylsilylene(alkylene)/l,4-phenylene] bearing Si—H moieties as well as poly(methylhydrosiloxane) are readily performed through Pt-catalyzed graft hydrosilylation with functionalized allyl ethers, 3-cyano-l-propene, and allyl carbamates in a manner similar to the process shown in equation 107 (vide supra)290,291. 

Ober and coworkers117 have grafted siloxanes onto a styrene-isoprene block copolymer via hydrosilylation of the pendant vinyl groups of the diene block with pentamethyldis-iloxane (30) (equation 12). 

Hydrosilylation is also a very useful chemical modification which leads to silane modified polymers with special properties [60-62]. Silane modified polymers have improved adhesion to fillers and better heat resistance. It also acts as a reactive substrate for grafting or moisture catalysed room temperature vulcanisation. Guo and co-workers [61] carried out catalytic hydrosilylation of BR using RhCl(PPh3)3 as the catalyst. Hydrosilylation reactions followed anti-Markovnikov rule as shown in the Scheme 4.4. 

In spite of the large number of grafted and side functionalized polysilox-anes commercially available and the variety of modification techniques available [25,50] (hydrosilylation, thiol-ene chemistry, halogen substitution, polycondensation), only a few of them have been used as in situ-formed graft copolymer compatibilizers. 

Gornowicz [135] grafted a fluorocarbon resin (e.g. either a homo- or copolymer of VDF) with siloxane to enhance its compatibility with PDMS. For example, vinyl triethoxysilane was first grafted onto fluorocarbon resin using peroxide. Then, an added silicone phase was vulcanizated via hydrosilylation. 

Abstract New polymeric supports, that can be used for preparation of novel catalytic systems, were obtained by grafting poly(vinylmethyl-co-dimethyl)siloxane arms onto multifunctional carbosilane moieties which belong to the class of exceptionally sterically hindered tris(silyl)methanes (Tj,.). Three types of Tj, molecules were applied 3-functional HCCSiMe Br) (type A), 9-functional HC[SiMe2(CHj)j-C (SiMejBr) ] (type B) and 4-functional Tg -derivative [SiMe2C(SiMe2Br)j]j (type C). The periphery-functionalized carbosilane-siloxane materials offer uniformly distributed and accessible sites for coordination of active catalytic species. New catalytic systems were thus prepared by coordination of platinum to vinyl moieties of the reported polymers, and used in hydrosilylation of vinyltrimethylsilane with 1,1,3,3-tetramethyldisiloxane. 

We have described a new system of polymeric snpports based on multifunctional, exceptionally sterically hindered carbosilane moieties, grafted with block poly(vinylmethyl-co-dimethyl)siloxane arms. They offer uniformly periphery-distribnted active sites (-CH = CH moieties) and can be used for preparation of novel catalysts. Platinum was thus attached to the polymers via coordination to vinyl gronps. The materials used in hydrosilylation of vinylsilanes can be considered as an alternative for traditional platinum catalysts. The utility of the catalysts seems to be dependent on the ratio [D]/[V] in the copolysiloxane arm. Those with too high amonnt of vinyl groups suffer from poor solubility and catalytic performance dne to excessive inter/intra-chain coordinative cross-linking. 

Cinchonidine displays a tertiary amine, an aromatic amine and a free hydroxyl functionality. Direct hydrosilylation with unprotected cinchonidine (derivatized with a double bond for hydrosilylation), led to a cross-linked product. Thus, hydrosilylation was performed on PHMS with the trimethylsilyl derivative 1 (Fig. 10), in the presence of (EtjS)jPtClj as catalyst (0.05%), for 6h at 80°C in toluene. The hydroxyl group was deprotected with methanol at 65°C during 120 h. Size Exclusion Chromatography showed that the polysiloxane backbone was not degraded. A maximal grafting percent of 15% could be obtained, relative to the SiH units. 

In order to understand the limitations and suggest improvements, the kinetics of the grafting reaction of P-cyclodextrin was investigated. Thus, the hydrosilylation reaction was run with either PMHS homopolymer or HMS-301 copolymer and stoichiometric amonnts of peracetylated monoallyl P-cyclodextrin in toluene solvent at 60°C. The kinetics was followed by IR analyses of the residual Si-H at 2160 cm [33]. Typical spectra are shown in Fig. 3. 

The main drawback of this method is that aminopolysiloxanes are not easily available in aU desired grafting ratios and molecular weights. Only a little range of MW (up to 8000) and grafting ratios (1-7%) are available commercially. This is due to limitations when polycondensation reactions are carried out with aminopropylsi-loxane units. Methods for obtaining aminopolysiloxanes by hydrosilylation, in their NH form suitable for nucleophilic reactions, are not available either. 

Attempts for Grafting Unprotected Sugars on Polysiloxanes by Hydrosilylation... 

Stadler et al. has synthesized several sugar-grafted polysiloxanes obtained by multistep procedures, including the preparation of the protected allyl-functionalized-sugars, the hydrosilylation with a statistical poly(dimethyl-co-hydrogenomethyl)-siloxane and finally the removal of the carbohydrate protective groups. 

Fig. 7 Hydrosilylation with trimethylsilyl protected allyl-grafted sugar followed by deprotection...

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