CONTRIBUTION TO A BETTER KNOWLEDGE OF THE CROSS-LINKING REACTION OF POLYDIMETHYLSILOXANE (PDMS) BY END-LINKING - THE FORMATION OF STAR-BRANCHED PDMS BY THE HYDROSILYLATION REACTION

Monofunctional polydimethylsiloxanes with a dimethylsilyl or a dimethy lsilylvinyl end-group were reacted with respectively 1,3,5,7-tetrameth yltetravinylcyclotetrasiloxane and 1,3,5,7-tetramethylcycloterasiloxan e. The hydrosilylation reaction, carried out in bulk and in the toluen e solution, were followed by FTi.r. spectrometry and the star-branched samples formed analysed by SEC-LS. In the second case, for PDMS silyl vinylic function at the chain-end, the reaction is noticeably faster a nd the final conversions reached are higher than in the first case. Th e principal parameter which limits the maximum conversion is the conce ntration of functional groups in the medium. Copyright (C) 1996 Elsevi er Science Ltd.