Scandium-Catalyzed Cyclocopolymerization of 1,5-Hexadiene with Styrene and Ethylene: Efficient Synthesis of Cyclopolyolefins Containing Syndiotactic Styrene-Styrene Sequences and Methylene-1,3-cyclopentane Units

The polymerization of 1,5-hexadiene (HD) and its copolymerization with styrene and ethylene by a series of half-sandwich scandium dialkyl complexes bearing various auxiliary ligands have been examined. Significant ligand influence on the catalytic activity and selectivity has been observed. The THF-free aminobenzyl scandium complex with a sterically demanding ligand, such as (C(5)Me(4)SiMe(3))Sc(CH(2)C(6)H(4)NMe(2)-o)(2) (4e), in combination with an equivalent of [Ph(3)C][B(C(6)F(5))(4)], serves as an excellent catalyst for the cyclocopolymerization of HD with styrene to afford a new family of polymer materials containing methylene-1,3-cyclopentane (MCP) units, vinyltetramethylene (VTM) units, and unique syndiotactic styrene-styrene sequences. By use of this catalyst, the terpolymerization of HD, styrene, and ethylene has also be achieved for the first time to afford novel cyclopolymer materials containing the five-member ring MCP units, ethylene-ethylene blocks, and syndiotactic styrene-styrene sequences. The composition of the copolymers can be controlled in a wide range simply by changing the comonomer feeding ratios. Most of the resulting copolymers show high melting points originating from the syndiotactic polystyrene blocks and polyethylene blocks well as in the case of the terpolymers.