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

Tanyaluck Mekpothi; Puttinan Meepowpan; Montira Sriyai; Robert Molloy; Winita Punyodom

doi:10.3390/polym13193374

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

Polymers (Basel). 2021 Sep 30;13(19):3374. doi: 10.3390/polym13193374.

Authors

Tanyaluck Mekpothi^{1

2}, Puttinan Meepowpan^{1

2

3}, Montira Sriyai^{3

4

5}, Robert Molloy^{4

5}, Winita Punyodom^{1

2

3

4

5}

Affiliations

¹ Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
² Center of Excellence for Innovation in Chemistry (PERCH-CIC), Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
³ Bioplastics Production Laboratory for Medical Applications, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
⁴ Center of Excellence in Materials Science and Technology, Chiang Mai University, Chiang Mai 50200, Thailand.
⁵ Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.

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 (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 (M¯w) = 4200-11,000 g mol^-1 and a narrow dispersity (Đ = 1.1-1.4).

Keywords: bromolactide; methylenelactide; poly(methylenelactide); poly(methylenelactide-g-L-lactide); ring-opening polymerization (ROP); thermal stability; vinyl addition polymerization.