Relationship between structure and properties in polydimethylsiloxane molecular composites

Poly(dimethylsiloxane) (PDMS) networks were prepared by tetrafunctionally endlinking hydroxyl terminated chains with tetraethoxysilane (TEOS). Molecular composites were prepared by in-situ base catalyzed reactions resulting in the formation of reinforcing fillers within the network. The resulting structure and growth process of the reinforcing fillers was studied using small-angle X-ray scattering (SAXS). Mechanical properties were examined by equilibrium stress-strain measurements.; The co-silica-titania reinforces the PDMS network better than silica or titania alone. The growth process proceeds by formation of uniform titania particles and then formation of larger silica particles. The titania reinforces the PDMS network well at small elongations. The in-situ titania reaction is very fast. Both systems yield dense particulates with fractally rough surfaces.; Poly(dimethylsiloxane) (PDMS) networks were prepared by tetrafunctionally endlinking hydroxyl terminated chains with tetraethoxysilane (TEOS). The resulting networks were filled in-situ by acid- and base-catalyzed reactions using novel precursors. The structures of the filler were examined by SAXS. The mechanical properties were determined using equilibrium stress-strain measurements.; Novel precursors with monomethoxy reactions sites on the silicon atoms did not generate stable filler particles. Those with trimethoxy groups on the silicon atoms did generate stable particulates. Only partially-hydolyzed TEOS provided reinforcement comparable to silica/PDMS systems.; Networks of PDMS were prepared by endlinking hydroxyl-terminated chains of varying molecular weights by TEOS. The resulting networks were filled in-situ by the sol-gel method generating silica particles. The resulting silica particles were examined by SAXS to determine the effects on silica particle formation as a function of molecular weight, weight percent filler, catalyst concentration, and swelling ratios (amount of precursor in the network).; Results show larger particle sizes with increasing molecular weights. Particle sizes are constant at low weight percents but show marked increases at higher filler concentrations. The swelling ratio, as expected, is in direct correlation to the mass of filler generated within the system. High catalyst concentrations result in larger particulates.