Chemical modification of poly(lactic acid) induced by thermal decomposition of N‐acetoxy‐phthalimide during extrusion

Abstract

Chemical modification of poly(lactic acid) (PLA) with N‐acetoxy‐phthalimide (NAPI) was performed in the melt by reactive extrusion, without using any peroxide initiator. The aminyl and nitroxide radicals produced from the NAPI thermal degradation, were, respectively, used (a) to create PLA macroradicals, and (b) to functionalize the PLA samples through nitroxide radical coupling. Depending on the extrusion temperature and the initial NAPI concentration, grafting rates up to 0.24 mol % were measured, modifying the PLA optical properties. This study represents an original new way of modification of PLA without the use of conventional peroxide initiators. Indeed, the undesirable side reactions (PLA branching or crosslinking) usually observed when using peroxides to initiate the radical grafting of PLA were avoided when using NAPI. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 120–129

Functionalization of poly(lactide) with N‐phenyl maleimide using N‐acetoxy‐phthalimide during reactive extrusion

“…The incorporation of PhM in the PLA during reactive extrusion also had an influence on the final macromolecular structure as revealed by SEC analyses. Indeed, we previously showed that the extrusion of PLA with NAPI led to an important decrease of the PLA average molar masses . As an example, adding 4 mol % NAPI during PLA extrusion led to decreases of 32 and 15 % for M n and M w , respectively, ( M n = 38.1 kg mol −1 ; M w = 73.5 kg mol −1 ; Table ) in comparison to the PLA sample extruded without NAPI ( M n = 55.9 kg mol −1 ; M w = 86.2 kg mol −1 ).…”

“…PLA was extruded with various PhM concentrations (from 0 to 4 mol %) in the presence of NAPI (Table ), and without any peroxide. Experiments were performed at 200 °C during 30 min, considering our previous results showing that NAPI had a higher degradation rate at an extrusion temperature of 200 °C compared to 180 °C . We also chose to limit the NAPI concentration at 4 mol % (10.2 wt %).…”

“…). We showed earlier that this increase of the UV absorption was linked to the grafting of moieties from NAPI decomposition onto the PLA backbone . When adding 0.5–4 mol % PhM in the PLA during reactive extrusion, a continuous increase of the UV absorption was then observed in the PLA elution domain (9–15 min; Fig.…”

“…A higher PhM homopolymerization at higher starting PhM concentrations could explain these results. As previously discussed, some nonextractable moieties, that is, PINO nitroxide or α,α′‐dioneaminyl‐based radicals were found to be grafted onto the PLA backbone (0.15–0.19 mol %; Table ). This grafting occurred probably upon the combination of PINO nitroxide or α,α′‐dioneaminyl‐based radicals, both originated from NAPI thermal decomposition, with the alkyl centered radicals created on the PLA backbone during the extrusion process.…”

“…In a lower extent, phthalimide‐ N ‐oxyl (PINO) radicals (nitroxide) were also formed and scavenged the macroradicals . In a recent paper, we showed that thermal degradation of NAPI during PLA reactive extrusion could be used to form PLA macroradicals, and to graft some nitroxides (up to 0.24 mol %) onto the PLA backbone, without the use of peroxide.…”