Selective Synthesis of 7-/14-membered Cyclic Carbonates by Temperature Gradient-Assisted Depolymerization and...

CO₂/epoxide copolymerization and ring-opening polymerization (ROP) of 6-membered cyclic carbonate have been widely used to prepare aliphatic polycarbonates (APCs) featuring 2- and 3-carbon spacer, respectively. However, the APCs with longer in-chain aliphatic spacer (≥ 4-carbon) were mainly prepared by step-growth-polycondensation, which generally suffered from harsh reaction conditions and low degree of control over molecular weight and chain microstructure. Herein, we presented a "temperature gradient-assisted" depolymerization strategy for selective synthesis of 7-membered cyclic 1,4-butylene carbonate (7-CBC) and its 14-membered dimer (7-CBC)₂. By using a highly active (amidoalkyl)pyridine-phenolate aluminum as catalsyt, both 7-CBC and (7-CBC)₂ underwent rapid ring-opening polymerization to afford poly(1,4-butylene carbonate) (PBC) with tailored molecular weight (from 27.3 kDa to 208.4 kDa), providing the opportunity to systematically investigate the effects of molecular weight on crystallinity, thermal, mechanical and rheology properties. PBC exhibited much superior mechanical strength and gas barrier property compared to high-density polyethylene (HDPE), low-density polyethylene (LDPE), and poly(ε-caprolactone) (PCL). This work resolved the synthetic challenges in the traditional step-growth-polycondensation and provided a powerful toolbox for developing high-performance aliphatic polycarbonates.