NEW MOLECULAR AND SUPERMOLECULAR POLYMER ARCHITECTURES VIA TRANSITION-METAL-CATALYZED ALKENE POLYMERIZATION

Superstructure formation during crystallization has been examined as a function of isotactic poly(propene) and poly(ethene) molecular archit ectures, tailored by means of metallocene catalyzed propene polymeriza tion, metallocene catalyzed ethene/alk-1-ene copolymerization, and nic kel-catalyzed migratory insertion polymerization of ethene to afford m ethyl-branched poly(ethene) without using comonomers. The role of ster ic irregularities in the chain resulting from false insertion in stere oselective polymerization or from short chain branching, respectively, was investigated. Randomly distributed regio- and stereo-regularities in isotactic poly(propene) chains and variation of crystallization te mperature were the key to controlled poly(propene) crystallization and predominant formation of the gamma-modification. Poly(propene) meltin g temperature increased with increasing isotactic segment length betwe en stereo- and regio-irregularities. Superstructures of isotactic gamm a-poly(propene) were analyzed by means of light and atomic force micro scopy. Both types of short-chain branched poly(ethene)s, prepared by e thene/oct-1-ene copolymerization and migratory insertion homopolymeriz ation, showed similar dependence of melting temperature on the degree of branching, calculated as the number of branching carbon atoms per 1 000 carbon atoms. Phase transitions were monitored by means of wide an gle X-ray scattering and pressure-volume-temperature measurements. Ato mic force microscopy was applied to image both lamella- and fringed mi celle-type superstructures as a function of the degree of branching.