Formation of poly(dimethylsiloxane) gels

One of the most important reactions used for room temperature vulcanization of elastomers, hydrosilylation, was investigated by end-linking samples of vinyl-terminated poly(dimethylsiloxane) (PDMS) with silanes having number-average functionalities of 3, 4, and 40-50. The reaction was monitored through SiH consumption up to and beyond the gel point via Fourier transform infrared spectroscopy (FTIR). Size exclusion chromatography (SEC) was used to determine the molecular weights of the sol fractions throughout the reaction. Gel samples were swollen in toluene so that the cycle rank (the proportion of useful intramolecular bonds) could be estimated. The experimental results were compared to results from simulations generated by Accelrys' polymer modeling software. The simulations were also used to predict fractions of loop and dangling chain defects in the gel and distributions of cycle ranks in the sol molecules. The success of this study should encourage extension to other systems, particularly the commercially important polyurethanes.