Silicone rubber copolymerization

Uses. There are about forty to fifty organic peroxides commercially available in more than seventy formulations designed for specific applications which include (1) initiators for vinyl monomer polymerizations, and copolymerizations of monomers such as vinyl chloride, ethylene, styrene, vinyl acetate, acrylics, fluoroolefms and buta-dienestyrene (2) curing agents for thermoset polyesters, styrenated alkyds and oils, silicone rubbers and poly allyl diglycol carbonates ... 

A rather similar dependence was observed by Hoffman et al. 98) for heparin covalently immobilized on silicone rubber, which had been pre-modified by graft-copolymerization of hydroxyethyl methacrylate and N-vinylpyrrolidone (Table 11). 

Hsuie, G.H. Lee, S.D. Chang, P.C. Kao, C.Y. Surface characterization and biological properties study of silicone rubber material grafted with phospholipid as biomaterial via plasma induced graft copolymerization. J. Biomed. Mater. Res. 1998, 42, 134-147. 

Some of the applications Include contact lenses, medical tubing and protective gas masks. The silicone rubber for these applications is optically clear because the silicone polymer and the reinforcing silica used to prepare the rubber are isorefractive at a specified temperature, usually about 25 C. The polymers which have been used are copolymers with sufficient phenyl substitution to raise the refractive index, from 1.4023 (for PDMS) to approximately 1.43 which is the refractive index of tri methyl si lyl treated fumed silica (e.g., Cabosll S-17). Such copolymers are prepared by copolymerizing (Me2S10)x and (PhMeSiO) or (Ph2S10)x using equilibrium conditions. 

Yang, J. and Hsiue, G. 1996. Synthesis of acrylic acid grafted silicone rubber via preirradiation graft copolymerization and its physical and dielectric properties. J Appl Polym Sci. 61 221-229. 

The polydimethylsiloxane rubbers (methyl silicone rubbers) have low TgS of about -123 C but stiffen at about -60°C due to crystallization. Copolymerization of the dimethyl dichlorsilane with an intermediate containing phenyl groups raises the Tg but if just sufficient is used to inhibit crystallization effectively the stiffening temperature can be reduced by some 30-40T. Such copolymers may also exhibit, like the dimethyl silicone rubbers, a very good thermal stability. 

Scheme 6 Silicone rubber 18 by copolymerization of an oligomeric dimettylsiloxane 15 with a vinyl-containing siloxane 16 and styrene-based monomer 17 using chloroplatinic acid.

Scheme 7 Siloxane-modified divinylbenzene telomer and octamer before copolymerization with styrene and divinyl benzene to give a silicone rubber.

Silicone Resins. Hydrolysis of (CH3)2SiCl2 produces linear flexible molecules for rubber. Hydrolysis of CH3SiCl3 produces highly cross-linked molecules for thermoset plastics. These are too cross-linked and brittle for most purposes. Useful thermoset plastics are prepared by copolymerizing difunctional and trifunctional monomers. In commercial practice, the ratio of difunctional to trifunctional is generally 80/20 to 40/60. For some products, methyl silicon may be partly replaced by phenyl silicon. 

---