Polylactic acid, maleic anhydride and dicumyl peroxide: NMR study of the free-radical melt reaction product

In this study, a detailed characterization was carried out of a product formed in the melt reaction of poly(lactic acid) PLA with maleic anhydride, initiated by dicumyl peroxide under the reaction conditions reported herein. The chemical structure of the reaction product was determined by 1H NMR and 13C NMR spectroscopy and by DEPT-135 and 13C-1H HSQC techniques. It was found that, under the conditions applied in this study, instead of the well-reported grafting of maleic anhydride onto the PLA, a product was formed from the reaction of two PLA macro-radicals, which probably occurs after the β-scission mechanism. The 13C NMR spectrum of the proposed reaction product was also calculated using the GIAO-DFT method and the result is in agreement with the experimental spectrum.