Aluminum-Catalyzed Ring-Opening Polymerization of Trimethylene Carbonate: A Route to Molecular-Weight-Controllable Cyclic Poly(trimethylene carbonate)

Cyclic polymers continue to attract significant interest in polymer science because of their distinctive looplike topology and the ongoing synthetic challenges associated with producing them with high purity and controllable molecular weight. In this work, we report the ring-opening polymerization of trimethylene carbonate (TMC) to synthesize cyclic poly(trimethylene carbonate) (cPTMC) using Schiff-base-ligated aluminum complexes as catalysts under mild polymerization conditions. The polymerization afforded highly cPTMC samples without no detectable linear contaminants under the applied analytical conditions, without requiring stringent polymerization conditions or postpolymerization purification, and the molecular weights could be readily adjusted by varying the molar ratio of TMC to catalyst. The formation of cyclic polymer was confirmed by NMR spectroscopy, MALDI-TOF mass spectrometry, TEM, DSC, and viscosity measurements. The generation of cPTMC is proposed to proceed via an intramolecular backbiting reaction mechanism.