Abstract
In this work, a novel poly (methylenelactide-g-L-lactide), P(MLA-g-LLA) graft copolymer was synthesized from poly(methylenelactide) (PMLA) and L-lactide (LLA) using 0.03 mol% liquid tin(II) n-butoxide (Sn(OnBu)2) as an initiator by a combination of vinyl addition and ring-opening polymerization (ROP) at 120 °C for 72 h. Proton and carbon-13 nuclear magnetic resonance spectroscopy (1H- and 13C-NMR) and Fourier-transform infrared spectroscopy (FT-IR) confirmed the grafted structure of P(MLA-g-LLA). The P(MLA-g-LLA) melting temperatures (Tm) range of 144–164 °C, which was lower than that of PLA (170–180 °C), while the thermal decomposition temperature (Td) of around 314–335 °C was higher than that of PLA (approx. 300 °C). These results indicated that the grafting reaction could widen the melt processing range of PLA and in doing so increase PLA’s thermal stability during melt processing. The graft copolymers were obtained with weight-average molecular weights () = 4200–11,000 g mol−1 and a narrow dispersity (Đ = 1.1–1.4).
Highlights
Poly(lactic acid) or polylactide (PLA), an aliphatic polyester derived from renewable starch-containing resources such as corn; sugar beet; and cassava, is one of the most significant biodegradable polymers extensively used as a petroleum-based materials replacement due to its biodegradability and environmentally-friendly properties [1,2,3,4,5,6,7,8,9,10,11]
Synthesis of Poly(methylenelactide) (PMLA) The synthetic pathway of PMLA is as shown in Scheme 2
The effect of the bromination reaction was the production of strong acids of hydrobromic acid (HBr) which was removed by using an excess of 0.2 M sodium bisulfite solution
Summary
Poly(lactic acid) or polylactide (PLA), an aliphatic polyester derived from renewable starch-containing resources such as corn; sugar beet; and cassava, is one of the most significant biodegradable polymers extensively used as a petroleum-based materials replacement due to its biodegradability and environmentally-friendly properties [1,2,3,4,5,6,7,8,9,10,11]. For the modification of PLA by copolymerization, most studies have been paying attention to the copolymerizing of the lactide with either lactide/lactone monomers or other monomers with functional groups such as amino and carboxylic groups, etc [34,35,36] The copolymers such as poly(lactide-co-glycolide) (PLGA), poly(lactide-co-ε-caprolactone) (PLCL), poly(lactic acid)-poly(ethylene oxide) (PLA-PEO) and poly(lactic acid-glutamic acid) (PLGM) are generally synthesized via ring-opening polymerization (ROP) of cyclic ester monomers [37,38,39]. These copolymers could synergistically combine the advantages of both components showing greater properties, overcome the limitations of the individual ones. The experimental conditions must be optimized in order to obtain the suitable polymerization process for the designed system
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