Block copolymers of ethylene and styrene prepared via chain shuttling polymerization

Block copolymer of ethylene and styrene exhibits excellent insulation properties and high dielectric energy density, and thus is a promising insulation material.[1] Unfortunately, to the best  of our knowledge, only the expensive scandium-based catalysts could catalyze E/St copolymerization to give block copolymer[2] since the insertion energy of St into titanium active species is much higher than that of E, leading to titanium-based catalysts to produce “pseudo random” E-St copolymers.[3]  It is very attractive and challenging to explore the economic approach to prepare E/St block copolymer. Chain shuttling polymerization (CSP) has exhibited unique privilege to synthesize block copolymer via cross-coordination chain transfer polymerization.[4] The challenge is to construct the catalytic systems. Herein, we were inspired by the fact that the rare-earth metal complexes except scandium complexes are active to syndiotactic styrene polymerization but incapable to ethylene polymerization, and the hafnium complexes are usually inert to styrene polymerization to construct the chain shuttling catalytic system by employing the pyridyl-methylene fluorenyl yttrium complex (1) and pyridylamide hafnium complex (2). In the presence of AliBu3 as chain shuttling agent, the binary catalytic system catalyzed E/St copolymerization to generate the block copolymer of ethylene and styrene contaminated by the homopolymer. The composition can be tuned through regulating the ratio of 1 to 2.