Anionic copolymerization of styrene and isoprene in cyclohexane

Abstract

AbstractThe copolymerization of isoprene with styrene initiated with sec‐butyllithium in cyclohexane solution has been studied by kinetic methods. The rates of the homopolymerization have been measured by normal methods. The rates of the cross‐propagation reactions were measured by the rate of appearance or disappearance of the ultraviolet absorption of polystyryllithium when the individual chain ends were reacted with the opposite monomer in the absence of the first. The rates of some of the reactions were also measured in the presence of the other monomer. It was found that polyisoprenyllithium reacted with both monomers with a one quarter‐order dependence, and the polystyryllithium with a one half‐order dependence. It was found possible to describe the copolymerization in terms of the four individual rate constants and to predict the initial copolymer composition. It was not found necessary to resort to explanations based on preferential absorption of isoprene around the chain ends to explain the high isoprene content of the copolymer.