Cobalt-catalyzed [2 + 2 + 2] cycloaddition copolymerization of diyne and internal alkyne monomers to highly branched polymers

Abstract

A novel synthetic method for hyperbranched polymers is reported. A cobalt catalyst previously developed in our group promotes the catalytic alkyne [2 + 2 + 2] cycloaddition polymerization of aromatic diynes with internal alkynes, which proceeds without gelation or production of insoluble materials to give the corresponding soluble polymer in good yields. The method is reproducible, and the polymerization behavior can readily be predicted by the results of model reactions. Thus, the molecular weight and a degree of branching (DB) of the resulting polymer can be controlled by selecting the internal alkyne monomer and its loading amount. The occurrence of effective endcapping reaction was confirmed by degradation of the polymer derived from a diyne bearing a silyl ether linker, and a high DB of more than 0.5 was obtained.