Novel Poly(Methylenelactide-g-L-Lactide) Graft Copolymers Synthesized by a Combination of Vinyl Addition and Ring-Opening Polymerizations

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 ((1)H- and (13)C-NMR) and Fourier-transform infrared spectroscopy (FT-IR) confirmed the grafted structure of P(MLA-g-LLA). The P(MLA-g-LLA) melting temperatures (T(m)) range of 144–164 °C, which was lower than that of PLA (170–180 °C), while the thermal decomposition temperature (T(d)) 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 ([Formula: see text]) = 4200–11,000 g mol(−1) and a narrow dispersity (Đ = 1.1–1.4).