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

The hydrogenation of styrene–butadiene copolymers of known global composition, monomeric distribution, molecular weight and microstructure is here reported. The saturation was carried out through a sequential polymerization–hydrogenation process which efficiency relies on the use of the polymerization solvent and initiator (cyclohexane and n-butyllithium) as the hydrogenation solvent and catalyst promoter, respectively. The SBRs, dissolved in cyclohexane, were homogeneously hydrogenated using a Ziegler–Natta type catalyst, prepared with nickel acetylacetonate and n-butyllithium. The only species, which was not present in both parts of the global process, is the catalyst for the homogeneous hydrogenation: nickel acetylacetonate. Three types of SBRs were investigated on the basis of their monomeric distribution: diblock (D-SBR), triblock with polystyrene extremes (T-SBR) and random (R-SBR). All the copolymers studied were synthesized by anionic solution polymerization. The precursors and corresponding hydrogenated polymers were analyzed by infrared spectroscopy (FTIR) and nuclear magnetic resonance (1HNMR) to determine the 1,2-vinyl and 1,4-trans double bond content in the butadiene portion of the copolymers. These data were used to calculate the saturation degree, X, considering the amount of double bonds of the precursor copolymers and the corresponding hydrogenated copolymer: X=(Ci0−Ci)/Ci0.