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

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.