Cross-Linking Of Methyl Silicone Rubbers. Part Ii. Analysis Of Extractables From Samples Cross-Linked Under Various Conditions

During the cross-linking under themal conditions of two pre-polymers, a variety of compounds may be formed in addition to the desired cross-linked network, i.e., branched chain, large ring, and linear chain of twice pre-polymer molecular weight. In order to evaluate these processes with as little chemical complication as possible, a series of two component methyl silicone pre-polymers (Sylgard 184, 186, and 188) have been cross-linked with vinyl silicone pre-polymer at various ratios of reactive groups and concentrations in silicone oil. These rubbers were evaluated by thermomechanical analysis (TMA) and then swollen with n-hexane. The cross-link density was evaluated from TMA and hexane swelling. The extracts were studied by gel permeation chromatography. As the “catalyst” concentration (active hydrogen containing pre-polymer) was increased from 5 to 60%, the percent and average molecular weight of the hexane-soluble fraction was found to decrease for the 186 and 188 samples. No higher molecular weight fraction was extractable from the. © 1974, Taylor & Francis Group, LLC. All rights reserved.