Vinyl polysiloxane

Pendergrass, P. B., Belovicz, M. W., and Reeves, C. A. (2003), Surface area of the human vagina as measured from vinyl polysiloxane casts, Gynecol. Obstet. Invest., 55,110-113. 

Gas chromatography is the method of choice for the determination of TCPM and TCPMe. Non-polar or medium-polar columns, such as DBS and CP Sil 8 (5% phenyl 95% dimethylpolysiloxane) [1, 4, 8], DB17 (50% phenyl 50% di-methylpolysiloxane) [4,10], and CP Sil 12 (58% CP Sil 8 and 42% CP Sil 19 (85% methyl 7% phenyl 7% cyanopropyl 1% vinyl polysiloxane)) [8] can be used. TCPM and TCPMe elute relatively late in the chromatograms, normally just before octachloronaphthalene, with GC oven temperatures around 270-300°C. Splitless injection can be used [8]. 

The grafting of the living vinylated polysiloxanes to the reactive groups (Si-Cl) on the silica sur ce occurs with a yield fiom 12 to 20%. In the same conditions, the polysiloxane bearing the phosphine groups is attached to the surface with a still low yield, about 14%. The characteristics of selected hybrids are presented in Table 1. Full details are described in Ref. [5]. 

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]. 

Two vinyl polysiloxane (silicone) impression materials [Examix Light-Body, GC America, Alsip, IL, USA Reprosil Light-Body, LD Caulk, Milford, DE,... 

Additional TMDSC study of other vinyl polysiloxane, polyether and polysulfide impression materials is important to verify if the polymer transitions shown in Figures 16 to 19 generally exist in different products and to investigate the effects of other temperature modulation conditions. Complementary research on correlations with clinically relevant mechanical properties of the elastomeric impression materials is needed to verify if these thermal analyses have useful predictive power. Interestingly, when compared at apparently similar viscosities, the reported values of the elastic modulus [3] are highest for the vinyl polysiloxane silicone impression materials, intermediate for the polyether impression materials, and lowest for the polysulfide impression materials, in reverse order to the relative values of Tg fovind in our thermal analyses [45]. Our X-ray diffraction and scanning electron microscopic study [47] of these impression materials has shown that they contain substantial amounts of crystalline filler particles in the micron size range, which are incorporated by manufacturers to achieve the clinically desired viscosity levels. Tliese filler particles should have considerable influence on the mechanical properties of the impression materials. 

Thermal cure system. The thermal cure system is based on a hydrosilylation addition reaction between vinyl-functionalized and silicon-hydrido functionalized polysiloxanes [32,33,35], Unsaturated organic groups react with a Si-H functionality in the presence of a platinum-based catalyst (Scheme 10). 

The physical properties of radiation and peroxide cured polysiloxanes have been compared by several investigators [402]. Vinyl-substituted (0.14 mol%) radiation-cured polysiloxane is found to have better strength properties than the chemically cured analogue. The phenyl substitution (7.5 mol%) has only marginal effect. The physical properties of radiation and thermally cured sUica-filled polyvinylethyldimethylsiloxane compounds are found to be similar. 

Thermal Transition Property Standard Polysiloxane Unmodified Phenyl Modified Phenyl-vinyl Modified... 

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