Cross-linking of linear vinylpolysiloxanes by hydrosilylation – FTIR spectroscopic studies

Abstract Linear polysiloxanes with regular vinyl group distribution along the chains, obtained by ring-opening polymerizations of 1,3,3,5,5-pentamethyl-1-vinylcyclotrisiloxane (D 2 V) and 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane (V 3 ) have been cross-linked with hydrogensiloxanes of various functionalities and molecular structures. The reactions have been performed in the presence of Karstedt's catalysts at equimolar ratios of reactive groups and followed by ATR-FTIR spectroscopy. It has been found that in none of the systems the cross-linking process proceeds completely. The highest amount of unreacted Si H groups has remained when tetrafunctional 2,4,6,8-tetramethylcyclotetrasiloxane (D 4 H ) has been used in the process, lower in the case of the reactions with tetrafunctional branched tetrakis(dimethylsiloxy)silane (Q(M H ) 4 ) and the lowest for linear difunctional 1,1,3,3-tetramethyldisiloxane ( H MM H ). The differences have been explained by differences in functionality and molecular structure of hydrogensiloxanes applied as cross-linking agents. Lower concentration of vinyl groups in D 2 V polymer than in V 3 polymer has facilitated its reaction with tetrafunctional hydrogensiloxanes as compared to the most reactive difunctional H MM H . Results of the studies may be helpful when planning application of polysiloxanes cross-linked by hydrosilylation as preceramic materials.