Poly -polysiloxane hydrosilylation

A very versatile and important methodology for controlling the properties of polysiloxanes involves hydrosilylation [eqn (10.33)]. Reaction of poly(methyl-hydrosiloxane) or poly(methylhydrosiloxane)-poly(dimethylsiloxane) copolymers with vinyl-capped species allows the introduction of side groups which give rise to a variety of interesting properties. 

Hydrosilylations of buckminsterfullerene (Cgo) with a poly(hydrosiloxane) (301) or H(SiMe20)3SiMe2H in the presence of Karstedt s catalyst (vide supra) proceed smoothly at 29 °C to give the corresponding (1 1) Cgo-polysiloxanes (302) with molecular weights of 5000 and 4000, respectively (equation 112)297. 

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. 

On the other hand, there is a need to use inhibitors of the platinum catalysts temporarily to reduce their catalytic activity in the presence of hydro- and vinyl-polysiloxanes in order to stop the curing process at room temperature, but to allow the platinum catalyst to be activated at elevated temperature. Among the principal types of compounds reported are alkenyl derivatives, esters of unsaturated acids, crown ethers, organic nitrogen compounds, phosphines, linear and cyclic vinyl-siloxanes, and poly(vinyl)siloxanes [2], and recently fumarate [44] and maleinate [33]. New co-activators of the catalysts (precursors) have been revealed in the 1990s to reduce to ppm the levels of platinum required to effect hydrosilylation curing [45, 46]. 

Polysiloxane random co-polymers (with molecular weights of 5,000-10,000) with pendant ferrocene groups have recently been synthesized 37 via hydrosilylation of vinylferrocene or 9-ferrocenyl-l-nonene with a poly(methylhy-drosiloxane)-r-poly(dimethylsiloxane) random co-polymer (Equation (12)). These materials were used as ampero-metric biosensors for the detection of glucose. In this case, the polymers effectively mediated electron transfer between reduced glucose oxidase and a conventional carbon paste electrode. The response of the sensor to glucose was dependent upon the nature of the polymeric backbone. The optimal response was achieved by finding a compromise between increased polymer flexibility and decreased spacing between individual relay (i.e., ferrocene) sites. 

The aim of the present work was the synthesis of alternating copolymers of tetramethyldisiloxane and different diolefinic molecules via hydrosilylation polyaddition followed by an equilibration reaction with SiH-containing polysiloxanes (PMHS) and poly(dimethylsiloxane) (PDMS) (see Schemes 1 and 2). 

The hydrosilylation processes of carbon-carbon multiple bonds, applied in the field of polymer chemistry and materials science, are described in part three (section 4) of this article. It includes functionalization (and cross-linking) of polysiloxanes and (poly)silsesquioxanes as well as hydrosilylation polymerization of difunctional organosilicon monomers besides the application of hydrosilylation in the synthesis of silicon-containing dendrimers and hybrid organic-inorganic materials. 

The hydrosilylation of 1-heptene, allyl glycidyl ether, and allylpolyether by heptamethyl(hydrosiloxane) and their respective polysiloxanes catalyzed by rhodium siloxide complex in imidazolinum ionic liquids, especially [TriMIM]MeS04, gives heptylglycidoxjdunctional (poly)siloxanes and silicone polyethers with high yield and selectivity. The catalytic system can be easily separated and successfully reused up to five times (123). 

Weyershausen group from Degussa have used a variety of platinum precatalysts such as K2[PtCl4] and [Pt(PPh3)4] dissolved in the ionic liquid [CyPy][BF4] and [C4-3-pic] [BF4] tested in the modification of polysiloxanes via the biphasic hydrosilylation of 1-hexadecene and terminal poly ether olefins (124). 

A slightly different but widely used variant of this method is a hydrosilylation reaction between reactive poly-siloxanes and the mesogenic monomers of the olefin type, which can be used for LC polysiloxanes ... 

Another well-known example pertains to polysiloxane- tocfc-polyamide diblock copolymers obtained by anionic copolymerization of -caprolactam from a poly-dimethylsiloxane (PDMS) macroinitiator the latter is prepared by hydrosilylation of the unsaturated moiety carried by an acyllactam, using a a-hydrogenated PDMS ... 

---