Temperature-Controlled Cyclic Polyester Molecular Weights in Ring-Expansion Polymerization

Ring-expansion polymerization of cyclic esters is a feasible approach to synthesize cyclic polyesters; however, controlling the molecular weight of cyclic polyesters is still a formidable challenge. In this work, the molecular weight of cyclic polyester can be easily controlled by regulating the polymerization rate and cyclization rate during a chain-growth polymerization process by adjusting the polymerization temperature. The molecular weights of cyclic polyesters (poly(salicylic phenyl glycolide)), ranging from 32.2 to 189.0 kg/mol, are controlled well because of an inverse relationship between the natural logarithms of molecular weights and temperatures. The molecular weights of cyclic polymers remain similar throughout polymerization, regardless of the different conversions at a fixed temperature. The cyclic structures of the polyesters are confirmed by gel permeation chromatography, mass spectrometry, and atomic force microscopy. Due to the incorporation of phenyl groups in the polymer side and main chains, the glass transition temperature can be as high as 116.6 °C.