Polylactic acid macromonomer radical propagation kinetics and degradation behaviour

Abstract

Polylactic acid ethyl ester methacrylate (PLA_NEMA) macromonomers are synthesized with N = 1, 5, 7, and 9 average number of polyester units. While propagation rate coefficients (k_p) determined by pulsed laser polymerization experiments for bulk PLA₁EMA and PLA₅EMA are not significantly different over the 40–100 °C temperature range, they are elevated by 60% compared to methyl methacrylate, indicating that the nature of substituents several units beyond the methacrylic group does not decisively impact bulk k_p measurements. Compared to bulk PLA₅EMA, the apparent k_p in 75 wt% n-butanol solution is enhanced due to hydrogen bonding, whereas in 75 wt% dimethylformamide solution it is reduced by 35% because of differences in macromonomer and solvent molar volumes. The PLA₅EMA macromonomers are used to produce nanoparticles (NP) by emulsion radical polymerization that degrade almost four times more slowly than NPs produced from their hydroxyl terminated macromonomer counterpart.