Thermoplastic elastomers from ni-catalyzed ?-olefins polymerization

Polymerization of ethylene by late transition metal complexes typically provides highly branched amorphous polymers through a chain-walking mechanism, while the chain-straightening polymerization of ?-olefins gives semicrystalline polymers. In this work the polymerization of 1-hexene, 1-octene and 1-dodecene by an ?-diimine Ni(II) complex in combination with diethylaluminium chloride is studied. The effect of monomer size and monomer concentration on activity, polymerization "livingness" and polymer structure - properties relationship , i.e., total branching, branch type and frequency, thermal and mechanical behavior, was investigated. While the length of the monomer dictates the competition between the chain-walking and the chain-straightening mechanism, thus influencing the overall branching content, the monomer concentration strongly affects the branching distribution. Under optimized conditions at ambient temperature, the polymerization of 1-dodecene proceeds in a quasi-living manner to give, in quantitative yield, semicrystalline poly(ethylene)-like materials with high molecular weight, narrow molecular weight distribution and melting temperature up to 81 °C. Additionally, semicrystalline/amorphous di- and tri-block copolymers were successfully synthesized by sequential monomer addition from 1-dodecene and ethylene. Mechanical investigation has shown that the block copolymers behave as thermoplastic elastomers with different performances, depending on the composition, length of the blocks and material's overall crystallinity. The results make this synthesis route attractive for the preparation of thermoplastic elastomers from readily accessible starting materials.