Cationic Zr catalysts for the sequential polymerisation of alkenes and cyclic oxygenated monomers

Abstract

Block copolymers (BCPs) featuring an apolar polyalkene and a polar polyester segment are attractive materials that can be synthesised through one-pot procedures with rare-earth metal catalysts, including those based on Sc. However, examples remain limited to the copolymerisation of conjugated olefins, such as isoprene and myrcene, with cyclic esters. While Zr is diagonally related to Sc in the periodic table, and Zr-based catalysts excel at non-conjugated olefin polymerisations, cationic Zr complexes remain unreported for apolar polyolefin/polar polyester BCPs. Here, we show that cationic Zr amine bisphenolate and zirconocene complexes are effective catalysts for the sequential polymerisation of various alkene and cyclic ester/ether monomers, yet deliver two separate homopolymers instead of copolymers. Mechanistic studies combined with DFT calculations suggest that the alkene monomer is polymerised via a coordination–insertion pathway, whereas ε-caprolactone polymerisation follows a cationic ring-opening mechanism under these conditions.