Advanced Polymerization and Properties of Biobased High Tg polyester of Isosorbide and 1,4-Cyclohexanedicarboxylic Acid through in Situ Acetylation

Abstract

The synthetic problems associated with melt polymerizations to form homopolyesters of isosorbide (ISB) and rigid diacids could potentially be solved by using catalyst systems with acetic anhydride (Ac2O). A catalyst consisting of dibutyltin oxide, germanium oxide, and Ac2O exhibited excellent performance characteristics in syntheses of a high-molecular-weight homopolyester of ISB and cis/trans-1,4-cyclohexanedicarboxylic acid (CHDA), also referred to as poly(isosorbide cis/trans-1,4-cyclohexanedicarboxylate) (PICD). The acetylation of ISB using Ac2O during esterification decreased the steric hindrance of ISB and accelerated the chain growth of PICD. Gel permeation chromatography data confirmed the formation of a high-molecular-weight PICD (71 100 weight-average molecular weight and 14 300 number-average molecular weight) using 0.02 mol of Ac2O. The glass transition temperature of PICD was almost 131 °C at 0.02 mol of Ac2O and decreased with increasing amounts of Ac2O due to the breaking of the rigid ring of ISB at higher concentrations of Ac2O. The structure of opened ring ISB was confirmed using two-dimensional nuclear magnetic resonance (NMR) and distortionless enhancement by polarization transfer NMR.