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 byortho-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 (TOFCr(III)= 1200 h−1vs.TOFAl(III)= 350 h−1, 1 mol% catalyst loadingvs.anhydride, 100 °C) and are significantly more active than the commercial catalyst for lactone ROP (TOFcr(III)= 3 h−1vs.TOFAl(III)= 300 h−1; 0.5 mol% catalyst loadingvs.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 (Mn= 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.