Abstract
Although the copolymerizations of l-lactide (LA) with seven- or six-membered ring lactones have been extensively studied, the copolymerizations of LA with four-membered ring lactones have scarcely been reported. In this work, we studied the copolymerization of LA with β-propiolactone (PL) and the properties of the obtained copolymers. The copolymerization of LA with PL was carried out using trifluoromethanesulfonic acid as a catalyst and methanol as an initiator to produce poly(LA-co-PL) with Mn of ~50,000 and PL-content of 6–67 mol %. The Tg values of the copolymers were rapidly lowered with increasing PL-contents. The Tm and ΔHm of the copolymers gradually decreased with increasing PL-contents, indicating their decreased crystallinity. Biodegradation test of the copolymers in compost demonstrated their improved biodegradability in comparison with the homopolymer of LA.
Highlights
Aliphatic polyesters such as poly(L-lactic acid) (or poly(L-lactide), PLA), poly(ε-caprolactone) (PCL), and poly(β-hydroxyalkanoate)s (PHAs) such as poly(β-hydroxybutyrate) (PHB) are known as typical biodegradable polymers [1,2,3,4,5,6,7]
PHAs including PHB were originally produced by fermentation with some bacteria [14,15], while the ring-opening polymerization of the corresponding four-membered ring lactones such as β-butyrolactone (BL) gives the structurally same polymers with PHAs [16,17]
The melting temperature (Tm), heat of fusion (∆Hm), and glass transition temperature (Tg) of the polymers were measured on a differential scanning calorimetry (DSC) using a DSC 6220 apparatus (Seiko, Tokyo, Japan)
Summary
Aliphatic polyesters such as poly(L-lactic acid) (or poly(L-lactide), PLA), poly(ε-caprolactone) (PCL), and poly(β-hydroxyalkanoate)s (PHAs) such as poly(β-hydroxybutyrate) (PHB) are known as typical biodegradable polymers [1,2,3,4,5,6,7]. Unsubstituted four-membered ring lactone, β-propiolactone (PL), can be subjected to ring-opening polymerization to form poly(β-propiolactone) (PPL) [16], which is known to show excellent degradability [18,19,20,21]. IInn oorrddeerr ttoo ssyynntthheessiizzee hhiigghh mmoolleeccuullaarr wweeiigghhtt ccooppoollyymmeerrss,, tthhee ffeeeedd mmoonnoommeerr ttoo iinniittiiaattoorr rraattiioo wwaass iinnccrreeaasseeddttoo775500//11. IInn tthhee ddeeggrraaddaattiioonntteesstt ((FFiigguurree 22)),, tthhee LLAA--PPLL ccooppoollyymmeerrss ddeeggrraaddeedd ffaasstteerr tthhaann PPLLAA hhoommooppoollyymmeerr. Could come from the inherent degradability of the PPL segment and/or the decreased crystallinity of the copolymers
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