New molecular and supermolecular polymer architecturesvia transition metal catalyzed alkene polymerization

Abstract

Superstructure formation during crystallization has been examined as a function of isotactic poly(propene) and poly(ethene) molecular architectures, tailored by means of metallocene catalyzed propene polymerization, metallocene catalyzed ethene/alk-1-ene copolymerization, and nickel-catalyzed migratory insertion polymerization of ethene to afford methyl-branched poly(ethene) without using comonomers. The role of steric irregularities in the chain resulting from false insertion in stereoselective polymerization or from short chain branching, respectively, was investigated. Randomly distributed regio- and stereo-regularities in isotactic poly(propene) chains and variation of crystallization temperature were the key to controlled poly(propene) crystallization and predominant formation of the γ-modification. Poly(propene) melting temperature increased with increasing isotactic segment length between stereo- and regio-irregularities. Superstructures of isotactic γ-poly(propene) were analyzed by means of light and atomic force microscopy. Both types of short-chain branched poly(ethene)s, prepared by ethene/oct-1-ene copolymerization and migratory insertion homopolymerization, showed similar dependence of melting temperature on the degree of branching, calculated as the number of branching carbon atoms per 1000 carbon atoms. Phase transitions were monitored by means of wide angle X-ray scattering and pressure–volume–temperature measurements. Atomic force microscopy was applied to image both lamella- and fringed micelle-type superstructures as a function of the degree of branching.