Biodegradability of unsaturated poly(ester-thioether)s synthesized by thiol-yne reactions

Abstract

We prepared the dialkynyl monomers 1,4-butanediol dipropiolate, meso-erythritol dipropiolate, and isomannide dipropiolate (IMDP) via the reactions of 1,4-butanediol, meso-erythritol, and isomannide, respectively, with propiolic acid. The thiol-Michael polyaddition of three dialkynyl monomers with several dithiols, namely, 1,4-butanedithiol, ethylene bis(thioglycolate), 3,6-dioxa-1,8-octanedithiol, D,L-dithiothreitol, and D-2,5-di-O-(2-mercaptoacetate)-1,4:3,6-dianhydromannitol (MAIM), proceeded in chloroform, tetrahydrofuran, or N,N-dimethylformamide (25 °C) using triethylamine as the catalyst to give unsaturated poly(ester-thioether)s with the expected structures (Mn, 2.4 × 103 to 22.6 × 103; molecular dispersity index [Mw/Mn], 1.26–2.00). All of the poly(ester-thioester)s had single glass-transition temperature (Tg) values between −27 and 49 °C. While the rigid main chains improved the glass transition temperature, all of the poly(ester-thioester)s showed apparent enzymatic hydrolysis by lipase but low biodegradability in biodegradation tests using activated sludge. The poly(IMDP-alt-MAIM) with the highest biobased degree (55%) showed the highest biodegradability (10%) and the highest Tg (49 °C), suggesting that dianhydrosugars are suitable as biomass for improving biodegradability as well as thermal properties. The thiol-Michael polyaddition of three dialkynyl monomers with several dithiols proceeded using triethylamine as the catalyst to give unsaturated poly(ester-thioether)s with the expected structures (Mn, 2.4 × 103 to 22.6 × 103; molecular dispersity index [Mw/Mn], 1.26–2.00). All of the poly(ester-thioester)s had single glass-transition temperature values between −27 and 49 °C. While the rigid main chains improved the glass transition temperature, all of the poly(ester-thioester)s showed apparent enzymatic hydrolysis by lipase but low biodegradability in biodegradation tests using activated sludge.