Synthesis and Biodegradability of Tartaric Acid-Based Poly(ester- thioether)s via Thiol-Ene Click Polymerization

Using scandium triflate [Sc(OTf)3] as a catalyst, chemoselective esterification of tartaric acids by 3-butene-1-ol was performed, and we produced three dialkene monomers: L-di(3-butenyl) tartrate (BTA), D- BTA, and meso-BTA. Thiol-ene polyaddition of these dialkenyl tartrates and dithiols including 1,2-ethanedithiol (ED), ethylene bis(thioglycolate) (EBTG), and D,L-dithiothreitol (DTT) proceeded in toluene at 70 degrees C under nitrogen to give tartrate-containing poly(ester-thioether)s (Mn, (4.2-9.0) x 103; molecular weight distribution (Mw/Mn), 1.6-2.5). In differential scanning calorimetry, the poly(ester-thioether)s showed single Tgs between -25 and -8 degrees C. In biochemical oxygen demand (BOD) tests using activated sludge, poly(L-BTA-alt-EBTG) and poly(L-BTA-alt-ED) showed 32 and 8% biodegradability, which is comparable to that of similar L-malate-containing poly(ester-thioether)s (23 and 13% biodegradation, respectively). Notably, we observed enantio and diastereo effects on biodegradation because poly(L-BTA-alt-EBTG), poly(D-BTA-alt-EBTG), and poly(meso-BTA-alt-EBTG) showed different degradation behaviors during the biodegradation test (BOD/theoretical oxygen demand (TOD) values after 28 days, 32, 70, and 43%, respectively). Our findings provide insights into the design of biomass-based biodegradable polymers containing chiral centers.