Ortho-vanillin derived Al(iii) and Co(iii) catalyst systems for switchable catalysis using ε-decalactone, phthalic anhydride and cyclohexene oxide

Abstract

Switchable catalysis is a useful one-pot method to prepare block polyesters utilising a single catalyst exposed to a mixture of monomers. The catalyst is switched between lactone ring-opening polymerization (ROP) and epoxide/anhydride ring-opening copolymerization (ROCOP) by controlling its chain-end chemistry. Here, novel aluminium(III) (1) and cobalt(III) complexes (2), coordinated by ortho-vanillin derived salen ligands, show excellent switchable catalytic activity and selectivity for the preparation of poly(ε-decalactone-block-cyclohexene phthalate-block-ε-decalactone) [PDL-b-PCHPE-b-PDL]. Both complexes have competitive activities with a commercial chromium salen catalyst for epoxide/anhydride ROCOP (TOF_Cr(III) = 1200 h⁻¹vs. TOF_Al(III) = 350 h⁻¹, 1 mol% catalyst loading vs. anhydride, 100 °C) and are significantly more active than the commercial catalyst for lactone ROP (TOF_cr(III) = 3 h⁻¹vs. TOF_Al(III) = 300 h⁻¹; 0.5 mol% catalyst loading vs. lactone, T = 100 °C). The catalysts are tolerant to low loadings (0.1 mol% vs. anhydride, 0.05% vs. lactone) and produce high molar mass triblock polyesters (M_n = 6–57 kg mol⁻¹). The efficient production of high molar mass polyesters allows for future optimization of the block polyester thermal–mechanical properties and applications.