Synthesis and Biodegradability of Poly(ester-urethane)s via the Thiol-Michael Polyaddition of Dianhydro Sugar-Based Diacrylates

Abstract

We prepared dianhydro sugar-based diacrylate monomers, d-2,5-di-O-(urethane ethylene acrylate)-1,4:3,6-dianhydroglucitol (AOIIS) and -1,4:3,6-dianhydromannitol (AOIIM), via the respective reaction of 1,4:3,6-dianhydroglucitol (isosorbide (IS)) and 1,4:3,6-dianhydromannitol (isomannide (IM)) with 2-isocyanatoethyl acrylate (AOI). The thiol-Michael polyaddition of the two dianhydro sugar-based diacrylate monomers with several dithiols (ethylene bis(thioglycolate)) (EBTG); 3,6-dioxa-1,8-octanedithiol (DODT); 1,2-ethanedithiol (EDT); dl-dithiothreitol (DTT); and d-2,5-di-O-(2-mercaptoacetate)-1,4:3,6-dianhydromannitol (MAIM) proceeded in N,N-dimethylformamide (40 °C) using triethylamine as the catalyst to give poly(ester-urethane)s with the expected structures (Mn, 8.4 × 103 to 164.6 × 103 molecular dispersity index [Mw/Mn], 1.32-2.47). All of the poly(ester-urethane)s had single glass-transition temperature (Tg) values between -32 and 36 °C. In biodegradation tests using activated sludge, poly(AOIIS-alt-DODT) and poly(AOIIS-alt-DTT) had little biodegradability, but poly(AOIIS-alt-EBTG), poly(AOIIS-alt-EDT), and poly(AOIIS-alt-MAIM) showed 9, 8, and 32% of biodegradation, respectively, after 28 days. Using a conditioned sludge activated by a model compound of poly(ester-urethane), the biochemical oxygen demand (BOD)/total oxygen demand (TOD) value increased to 59% because the number of organisms able to degrade poly(AOIIM-alt-EBTG) was increased in the conditioned sludge relative to the natural sludge. Poly(AOIIS-alt-EBTG) also showed 36% of biodegradation in the activated sludge, indicating diastereo effects on biodegradability.