Ni(II)-diimmine-catalyzed 1-dodecene polymerization: thermoplastic elastomers of block copolymers

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-dodecene by an ?-diimine Ni(II) complex in combination with diethylaluminium chloride is studied. The effect of monomer concentration on activity, polymerization "livingness" and polymer structure-properties relationship, i.e., total branching, branch type and frequency, thermal and mechanical behavior, is investigated. 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. The living/controlled polymerization of 1-dodecene provides a viable access to precise synthesis of block copolymers. The fabrication of tri-block copolymer, composed of an amourphous middle-block, and di-block copolymer is completed by successive addition of 1-dodecene and ethylene, without requiring any intermediate separation step. Although chemically identical, each block exhibits distinct features, varying from semicrystalline to amorphous, taking advantage of the different polymerization mechanism involved in the polymerization of 1-dodecene and ethylene. Investigation on mechanical behavior by uniaxial stretching until failure and step-cycle tensile tests shows that the block copolymers behave as thermoplastic elastomers with different performances depending on the composition, length of the blocks and crystallinity. We demonstrate that this approach is a route to fabricate thermoplastic elastomers from readily accessible starting materials.