The present invention relates to a process for selectively hydrogenating a block copolymer having at least one butadiene polymer block and at least one isoprene polymer block with a hydrogenation catalyst that hydrogenates isoprene blocks and butadiene blocks at a different rate, which process comprises (a) choosing a desired polymer molecular weight and a desired level of residual unsaturation in the isoprene block(s) and in the butadiene block(s) and determining the molecular weights of the butadiene block(s) and isoprene block(s) such that the time required to hydrogenate the butadiene block(s) and isoprene block(s) with the hydrogenation catalyst to the desired residual unsaturation levels is substantially the same; (b) anionically polymerising butadiene and isoprene to form a block copolymer as determined in step (a); and (c) selectively hydrogenating the block copolymer with the hydrogenation catalyst until the butadiene block(s) and/or the isoprene block(s) have reached the desired level of residual unsaturation. The present invention further relates to embodiments in which either the isoprene or butadiene block(s) molecular weight(s) are chosen. According to yet another embodiment both the isoprene and the butadiene block(s) molecular weights are chosen and the microstructure adapted such that the time required to hydrogenate the butadiene and isoprene blocks is substantially the same.
Minimum residence time hydrogenation process for polyisoprene-polybutadiene block copolymers