Dehydrogenation of poly(1,3‐cyclohexadiene)–polystyrene binary block copolymers

The dehydrogenation of poly(1,3‐cyclohexadiene)–polystyrene binary block copolymers obtained by anionic copolymerization with alkyllithium/amine systems was investigated for the first time. The dehydrogenation of the poly(1,3‐cyclohexadiene) block, which was composed of 1,2‐cyclohexadiene (1,2‐CHD) and 1,4‐cyclohexadiene (1,4‐CHD) units, was strongly affected by the polymer chain structure. The existence of 1,2‐CHD units prevented the dehydrogenation of the poly(1,3‐cyclohexadiene) block in the binary block copolymer. The rate of dehydrogenation was fast on a long sequence of 1,4‐CHD units, whereas it was relatively slow for 1,2‐CHD/1,4‐CHD (≈1/1) unit sequences. The bonding of the polystyrene block to the polymer chain effectively improved not only the rate of dehydrogenation of a long sequence of 1,4‐CHD units but also that of the polymer chain with a high content of 1,2‐CHD units. The dehydrogenation of a poly(1,3‐cyclohexadiene) block containing a small number of 1,2‐CHD units progressed via step‐by‐step reactions. The dehydrogenation of a long sequence of 1,4‐CHD units proceeded as the first step. Subsequently, in the second step, the 1,2‐CHD/1,4‐CHD (≈1/1) unit sequences remaining in the polymer chain were dehydrogenated.