Preparation and properties of PDMS elastomer cross-linked with hydrolyzate of tetraethoxysilane, hexaethoxydisiloxane, and octaethoxytrisiloxane: influence of cross-linker structure.

Ethoxysilanes were hydrolyzed, and the resulting hydrolyzates were dimethylsilylated to produce Si–H terminated oligosiloxanes (CLs). These CLs were characterized using gel permeation chromatography, nuclear magnetic resonance, and Fourier-transform infrared spectroscopy. The results indicated the formation of highly condensed cyclic siloxanes, four-membered cyclic siloxanes, and linearly condensed cyclic siloxanes when derived from tetraethoxysilane, hexaethoxydisiloxane, and octaethoxytrisiloxane, respectively. The CLs were subsequently reacted with vinyl-terminated polydimethylsiloxane in the presence of the Karstedt catalyst to yield PDMS elastomers, which are comprised of di- and quadra-functional silicones. Tests for transmittance, thermal properties, tensile strength, and swelling in toluene were conducted to assess the impact of the molecular weight and microstructure of the CLs on the final products. As the number of silicon atoms in the ethoxysilanes increased, there was a rise in the secant modulus and a reduction in the degree of swelling. These findings suggest that the structure of PDMS elastomers can be tailored by varying the structure of the ethoxysilanes used as a cross-linking agent. Highlights: Si–H terminated oligosiloxanes were synthesized from hydrolyzates of tetraethoxysilane, hexaethoxydisiloxane, or octaethoxytrisiloxane and chloro(dimethyl)silane. PDMS elastomers were synthesized via the hydrosilylation of the Si–H terminated oligosiloxanes with vinyl-terminated polydimethylsiloxane. Secant modulus increased, while the degree of swelling decreased, with an increase in the number of silicon atoms in ethoxysilanes. Mechanical testing and the swelling test in toluene demonstrated that the structure of PDMS elastomers can be influenced by the structure of ethoxysilanes used as a cross-linking agent. [ABSTRACT FROM AUTHOR]