Isohexide hydroxy esters: synthesis and application of a new class of biobased AB-type building blocks

Abstract

Here we present the synthesis of a new family of sugar derived 1,4:3,6-dianhydrohexitol based AB-type monomers, containing one methyl ester group and a secondary hydroxyl group in all four possible stereo isomers (RR, RS, SR, SS). Structural characterization of the monomers (5a–d) was established by 1D and 2D NMR analysis, which was further confirmed by single-crystal X-ray structure determination. The application of these monomers in step-growth polymerization afforded fully isohexide based stereo-regular polyesters. Homo polyesters based on the RR and RS monomers were obtained with reasonable molecular weights by melt polymerization (M_n 2400 and 2500 resp.). These materials showed unexpectedly low glass-transition temperatures of 20 °C and 15 °C respectively. In contrast, the monomers with SR and SS configuration yielded only low molecular weight oligomers. Surprisingly, copolymerization of the RR and SR monomers gave a polyester with higher molecular weight (M_n 4100) and a high T_g of 80 °C. These preliminary results show that isohexide hydroxyesters are an intriguing new class of biobased building blocks with many potential applications.