The role of 2,3-butanediol stereochemistry in polyester synthesis

Abstract

The shift toward sustainable platform chemicals enables the development of innovative, renewable polyesters that can potentially compete on performance. 2,3-Butanediol (2,3-BDO) is a monomer that can be produced from biomass and it can increase the glass transition temperature of the polyesters it is incorporated into. The use of biotechnological routes will generate either a pure form or a mixture of the 2,3-BDO stereoisomers. To assess potential differences in reactivity of these stereoisomers, several catalysts were tested in a model transesterification reaction of phenyl benzoate with meso- and R,R-2,3-BDO. After ∼1 h, some catalysts, such as calcium acetate, did not show significantly different results in phenyl benzoate conversion between stereoisomer batches. Other catalysts, such as zirconium butoxide, showed higher yields when a batch of R,R-2,3-BDO was used. The opposite was observed for titanium butoxide, which showed more promising results for meso-2,3-BDO. Next, these zirconium and titanium butoxide catalysts were used for polymerization reactions with dimethyl terephthalate, resulting in similar trends for the different stereoisomers as was observed for the model reaction. The thermal degradation curves of the meso- and R,R-2,3-BDO-based terephthalate polyesters were similar, and no crystallinity was observed for either polyester. The catalysts La(acac)₃ and Zn(OAc)₂·2H₂O gave the highest yields in the transesterification model reaction. However, in polymer synthesis, both catalysts failed to reach the desired near-quantitative conversion with the commercial 2,3-BDO isomer mixture. Thus, the model transesterification reaction cannot be used to predict performance in polymer synthesis, but it can provide useful insight into performance trends related to 2,3-BDO stereochemistry.