Liquid Silicone Rubber Vulcanizates: Network Structure - Property Relationship and Cure Kinetics

Liquid silicone rubber (LSR) vulcanizates have been prepared from vinyl-end capped polydimethylsiloxane (PDMS) and polymethylhydrogenosiloxane (PMHS) in presence of platinum catalyst using solution casting technique. The science involving synthesis of usable silicone rubber by curing with polymethylhydrogenosiloxane has been studied in details. The effects of vinyl content of PDMS and the ratio of hydride crosslinker to vinyl concentration on crosslink density, mechanical, dynamic-mechanical and thermal properties have been discussed. It has been found that at optimum level of crosslinker, the LSR vulcanizate shows a maximum crosslink density with highest improvement in mechanical and thermal properties. The amount of crosslinker required, depends upon the number of vinyl functionality per unit length of the polymer chain and the chemical composition of the hydride crosslinker. This study makes a novel attempt to determine cure kinetics of PDMS by using Fourier Transform Infrared spectroscopy. Measurements have been done at three different temperatures and found to follow the first order reaction with respect to consumption of vinyl (C=C) and silyl hydride groups (Si-H). The activation energy and kinetic parameters have been determined as well.