Biodegradability of poly(ester-thioether)s containing chiral biomass via a Michael-type thiol-ene click reaction

Abstract

We prepared dianhydrosugar-based diacrylates: isosorbide bis(acrylate) (ISDA) and isomannide bis(acrylate) (IMDA) from the corresponding dianhydrosugars. Using a scandium triflate as the catalyst, the chemoselective dehydration of D-, L-, and meso-tartaric acids with 2-mercaptoethanol selectively synthesized three dithiols: L-bis(2-mercaptoethyl)tartrate (META), D-META, and meso-META. The thiol-Michael click polyaddition of ISDA or IMDA with the three dithiols proceeded in N,N-dimethylformamide (40 °C) using triethylamine as the catalyst, yielding the expected six poly(ester-thioether) diastereomers (M_n, 8.2 × 10³ to 9.2 × 10³; molecular weight distribution (M_w/M_n), 1.29–1.51). The synthesized poly(ester-thioether)s showed a single glass transition temperature (T_g) between −8 and 14 °C. In biodegradation measurements, monitored by biochemical oxygen demand (BOD) values in active sludge, poly(IMDA-alt-meso-META), poly(ISDA-alt-L-META), and poly(ISDA-alt-D-META) showed lower biodegradability. In contrast, poly(IMDA-alt-L-META), poly(IMDA-alt-D-META), and poly(ISDA-alt-meso-META) showed 16% to 28% biodegradation after 30 days, indicating diastereomeric effects on biodegradability. Since enzymatic hydrolysis using lipase showed a similar trend to the BOD tests, we concluded that biodegradability depends on the stereochemistry along the polymer backbone.