Polymerization of isoprene and butadiene with unparalleled stereoselectivity catalysed by rare-earth metal cationic species bearing a novel tridentate ligand†

Rare-earth metal complexes bearing a novel tridentate ligand with a phenylthiol sidearm have been synthesized. The corresponding rare-earth metal cationic species, with the exception of the lutetium-based complex, showed unparalleled stereoselectivity in the polymerization of isoprene and butadiene to respectively produce cis-1,4-polyisoprene and trans-1,4-polybutadiene. The unusual reactivity ratio in the yttrium-catalyzed copolymerization of isoprene and butadiene (r_IP = 2.61 and r_BD = 0.57) suggested that the generated copolymer possessed a unique sequence distribution. The excellent livingness of the reactions enabled the yttrium-based catalytic system to produce isoprene-butadiene block copolymers, which could be completely hydrogenated to serve as thermoplastic elastomers. Stress–strain experiments and hysteresis testing revealed the pivotal role that the sequence length plays in determining the mechanical properties of the hydrogenated copolymers.