Towards a better control of the radical functionalization of poly(lactic acid)

A deepening insight the radical functionalization of poly(lactic acid) is here reported with new chemical approaches to control the grafting level and the ultimate structure by stabilizing the macroradical intermediates. The radical functionalization of poly(lactic acid) (PLA) with maleic anhydride (MA) was thoroughly investigated using different chemical approaches with the purpose of controlling both the grafting degree and the structure/architecture of the final products. First, a new methodology was developed able to provide clear evidence of the grafting and to identify the structure of the inserted groups. The method consists in the derivatization reaction of the grafted succinic anhydride with a fluorescent derivative (1-naphthylmethylamine), which allows the functionalization to be assessed qualitatively and quantitatively and therefore improves understanding of the radical functionalization mechanism. Then, in order to control the incidence of secondary reactions, which affect the radical process in the presence of MA, new chemicals were investigated as functionalizing agents or as functionalizing co-agents together with MA. Butyl 3-(2-furyl)propenoate was used as a functional molecule capable of stabilizing the macroradical intermediate and then controlling the ?-scission reaction. 4-Benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl was tested as a radical mediator capable of modulating the insertion of MA through a simple reversible coupling reaction. The results obtained by both approaches suggest the possibility of stabilizing the PLA macroradical intermediates and accordingly keeping the radical process under control. © 2014 Society of Chemical Industry.