Siloxanes vinyl groups

The synthesis of the monomer for Cyclotene resins (Equation 13) is accompanied by the formation of by-products that derive from internal rather than terminal aryl attack on the vinyl group. Further decrease of selectivity is caused by aryl attack on only one of the terminal carbon atoms of the two siloxane vinyl groups and by hydrogenolysis at the C-Si bond carbons, followed by aryl group attack on the terminal or the internal carbon atom of the vinyl group thus formed. 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

The TOFSIMS results thus indicate that the surface of the silane film consists mainly of a random mixture of partly oxidized vinylbenzyl groups and the silane end of the molecules. The silanol groups have formed siloxane groups to some extent and some crosslinking of the molecules has occurred via the vinyl groups. 

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). 

Fig. 12. Production diagram of polymethyl(phenyl)siloxanes with active hydrogen atoms and vinyl groups at the silicon atom 1 - 7, 9 - batch boxes 8, 17 - mixers 10 - hydrolyser 11, 15 - collectors 12 - nutsch filter 13 - vacuum distillation tank 14 - cooler 16 - settling box...

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. 

At present we are engaged in the preparation of siloxane polymers and block copolymers with a larger number of ftinctional groups attached to the chain. In the following we report on siloxanes containing vinyl groups. 

The syntheses of siloxanes with vinyl groups at the silicon atoms of the chain was performed by anionic ring-opening polymerization of vinyl group-containing cyclotri- or cyclotetrasiloxanes (03, 04 ) with alkyl lithium compounds as initiators. The polymerizations were terminated by chlorosilanes with additional silico- or carbofunctional groups or octyl groups. In the block copolymerizations we used 03 or 04 and hexamethylcyclotrisiloxane (D3) (Scheme 1 and 2). 

Vinyl-terminated polydimethyl siloxanes react with hydrogen silanes according to second order kinetics. The same kinetics are found in model reactions on monofunctional reactants at a lower concentration range. Also, a direct proportionality between the rate of reaction and platinum concentration is observed in both cases. Network formation does not inhibit the reaction. Polymers with lateral vinyl groups and very short chain polymers with vinyl end groups have q)proximately zero order kinetics with... 

In a modem variant of this vulcanization reaction, polysiloxanes containing a small amount, <1%, of methylvinylsiloxane groups are the starting materials. Aryl or alkyl peroxides are again used to initiate cross-linking, but the chemistry now involves radical addition to vinyl groups on neighboring siloxane chains, depicted in Scheme 1. 

A vinyl-terminated siloxane polymer is mixed with a compound containing several Si H groups, such as dJ, (MeSiHO)4 in the presence of a platinum catalyst, hydrosilation takes place to give Si H2 H2-Si crosslinks (equation 27). A related platinum-catalyzed system employs two siloxane prepolymers, one containing some Si H bonds and the other Si vinyl groups. The platinum catalyst is active in extremely small amounts, so that its use is practical despite the high cost of platinum. 

A pair of vinyl or other unsaturated groups could also be joined by their direct reactions with free radicals. Similar end groups can be placed on siloxane chains by the use of an end blocker during polymerization (16). Reactive groups such as vinyl groups can be introduced as side chains by random copolymerizations involving, for example, methylvinylsiloxane tri-mers or tetramers (7),... 

The silanone route of functionalization of siloxanes turned out to have a high fimctional group tolerance - not only alkoxy and vinyl group can thus be inserted into siloxane molecules, but also NH2, Cl, CF3 and CN (Table 1). In the following, these groups can be used for additional specific functionalization, grafting, or special cure of these siloxanes. 

Hydrosilylation of unsaturated organosilicon compounds has also found several applications in molecular and polymer organosilicon chemistry. In particular, the addition of polyfunctional silicon hydrides to poly(vinyl)organosiloxane, catalyzed exclusively by Pt compounds and providing an activated cure for silicon rubber [10], has been of great practical importance. Hydrosilylation of the vinyl group at silicon seems to be effective synthetic method for preparation of oligomers and polymers with a linear or cyclolinear stmcture (polyhydrosilylation), and can occur either via the addition of dihydro-carbosilanes and -siloxanes to divinyl-silanes and -siloxanes [25, 26] or by intermolecular hydrosilylation [4] (eq. (1)). 

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