CATALYTIC-HYDROGENATION OF DIENE POLYMERS .1. KINETIC-ANALYSIS AND MECHANISTIC STUDIES ON THE HYDROGENATION OF POLYBUTADIENE POLYMERS IN THE PRESENCE OF RHCL(PPH3)3

Chemical modification of diene-based polymers via catalytic hydrogenation offers an efficient synthetic route to elastomers with high stability to oxidative degradation. Detailed kinetic studies involving the hydrogenation of cis-1,4-polybutadiene have been carried out in the presence of RhCl(PPh3)3 under mild reaction conditions (65 -degrees-C, < 101 kPa H2). Quantitative hydrogenation of carbon-carbon unsaturation has been achieved without any large scale changes in polymer chain length properties. Polymer structure characterization was accomplished using IR, H-1 and C-13 NMR spectroscopies. Based on detailed kinetic studies, a mechanism was postulated for the hydrogenation system in order to appreciate the important factors which influenced the nature and extent of the hydrogenation reactions. A rate law was derived from the proposed mechanism. Using this rate law model, statistical analysis of the experimental data has led to the successful estimation of reaction parameters. The selectivity of the catalyst for cis versus trans internal double bonds was also investigated, and the results show that steric effects are important for the catalyst selectivity. It was also found that catalytic hydrogenation of monodisperse polybutadiene could be used to produce monodisperse polyethylene or poly(ethyleneco-butylene) standard for gel permeation chromatography (GPC).