Polymerization of methylenecyclobutane,synthesis of an isopolyisoprene

The polymerization of methylenecyclobutane¹ in presence of LEWIS acids, and in presence of catalyst systems prepared from compounds of transition metals of Groups IV, V, VI, and VIII of the Periodic Table is discussed. The polymers obtained contained both mixed and unmixed cyclic and ethylenic structures. In cationic polymerization, cyclobutane structures predominate and coexist with structures comparable to those of a cyclised polyisoprene. With ZIEGLER-NATTA catalysts, the predominant structures are of the cyclised or uncyclised polyene type. It is only with certain transition metals of Groups IV, V, and VI, and especially with vanadium and chromium, that the polymers possess an isorubber structure, in which the C?C double bonds are in the exo position with respect to the chain. This isorubber cannot be obtained directly from an acyclic ethylenic monomer. It is also true that this isorubber is not obtained by simple opening of the small methylenecyclobutane ring; the exo methylene group of the monomer is different from that which appears in the structural unit of the polymer, because a ?non-classical”? alkyl bicyclobutonium ion takes part in the polymerization process.