Synthesis and Characterization of Biobased Polyester Containing Isosorbide

Abstract

Advanced synthetic method to improve the low reactivity of isosorbide for the biobased polyester polymerization was investigated using acetic anhydride and ethylene glycol as a reliever of steric hindrance and a chain linker, respectively. The analysis of two dimensional nuclear magnetic spectroscopy, reactivity calculation by Fukui functions and sequence distribution were carried out in order to prove the effect of acetic anhydride and ethylene glycol during the polymerization process. In addition, thermal properties and crystallization kinetics were also studied. At the first chapter, 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 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 was performed to confirm the formation of a high-molecular-weight PICD (71,100 weight average molecular weight and 14,300 number average molecular weight) using 0.02 mole of Ac2O. The glass transition temperature of PICD was almost 131oC at 0.02 mol 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. Finally, we proposed infinite loop mechanism via in situ acetylation. At the second chapter, a solution for overcoming the low reactivity of terephthalic acid and isosorbide (ISB) is proposed that uses 1,4-cyclohexane dimethanol and ethylene glycol. Using the different reactivities, volatilities, and degree of steric hindrances among the three diols, a highly heat-resistive biobased terpolyester (PEICT; glass transition temperature = 93–143°C) was synthesized with a high degree of polymerization (weight-average molecular weight 65,400; number-average molecular weight 25,400). After esterification, most of the oligomer end groups were found to consist of ISB, which decreases the overall reactivity of transesterification due to its characteristics. However, this end group changed gradually into ethylene units, which accelerated the transesterification and chain growth in the polycondensation process via chain scission at the carbonyl carbon adjacent to the ethylene unit. To substantiate this mechanism, the Fukui function was used to calculate the reactivity difference between monomers. The sequence distribution was analyzed using 13C-nuclear magnetic resonance to elucidate the function of each diol unit in transesterification. Finally, a polycondensation process with the effect of ethylene glycol as a chain linker for the PEICT terpolyester is proposed.