Selective hydrogenation of butadiene-styrene copolymers using a Ziegler-Natta type catalyst 1. Kinetic study

The hydrogenation of styrene-butadiene copolymers of known global compositi on, monomeric distribution, molecular weight and microstructure is here rep orted. The saturation was carried out through a sequential polymerization-h ydrogenation process which efficiency relies on the use of the polymerizati on solvent and initiator (cyclohexane and n-butyllithium) as the hydrogenat ion solvent and catalyst promoter, respectively. The SBRs, dissolved in cyc lohexane, were homogeneously hydrogenated using a Ziegler-Natta type cataly st, prepared with nickel acetylacetonate and n-butyllithium. The only speci es, which was not present in both parts of the global process, is the catal yst for the homogeneous hydrogenation: nickel acetylacetonate. Three types of SBRs were investigated on the basis of their monomeric distribution: dib lock (D-SBR), triblock with polystyrene extremes (T-SBR) and random (R-SBR) . All the copolymers studied were synthesized by anionic solution polymeriz ation, The precursors and corresponding hydrogenated polymers were analyzed by inf rared spectroscopy (FTIR) and nuclear magnetic resonance ((HNMR)-H-1) to de termine the 1,2-vinyl and 1,4-trans double bond content in the butadiene po rtion of the copolymers. These data were used to calculate the saturation d egree, X, considering the amount of double bonds of the precursor copolymer s and the corresponding hydrogenated copolymer: X = (C-i0 - C-i)/C-i0. (C) 2000 Elsevier Science Ltd. All rights reserved.