Isomerization Polymerization of 4-Alkylcyclopentenes Catalyzed by Pd Complexes: Hydrocarbon Polymers with Isotactic-Type Stereochemistry and Liquid-Crystalline Properties

摘要

The physical properties of poly(α-olefins) vary to a large degree depending on the alkyl substituents derived from the monomer and the relative stereochemistry of the neighboring repeating units (tacticity). Polymers with five- or six-membered rings in the monomer units have unique thermal and optical properties.1 Early transition-metal complex-catalyzed polymerization of cyclic olefins and cyclopolymerization of dienes provide these polymers efficiently, although polymerization with regulated tacticity is rare. Ni- or Pd-diimine complexes catalyze the polymerization of α-olefins and cyclopolymerization of dienes with isotactic selectivity when a C_2-symmetric ligand is employed. The polymerization reactions, including cyclopolymerization of monoterminal dienes, involve isomerization of the growing polymer end via a chain-walking process. In this paper, we report polymerization of 4-alkylcyclopentenes catalyzed by Pd complexes to afford polymers with 1,3-disubstituted five-membered rings formed via olefin insertion and chain walking. The polymer with regulated tacticity exhibited liquid-crystalline properties.