Post-polymerization modification of poly(lactic acid) via radical grafting with itaconic anhydride

• Poly(lactic acid) grafted was grafted with itaconic anhydride in melt.
• Reaction temperature 190 °C was applied with respect to properties of initiator.
• Side reactions were detected as a result of different concentration of reactants.
• Grafting yield strongly depends on concentration of both monomer and initiator.
• Melt behavior of grafted poly(lactic acid) change due to side reactions.

Poly(lactic acid) (PLA) was functionalized via radical grafting with itaconic anhydride (IAH) in melt. Reaction was initiated using 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (L101). Experiments were achieved in order to determine the relationship between reaction conditions and grafting yield, whereas different concentrations of IAH (0.5–10 wt%) and L101 (0.1–2 wt%) were used for reaction. Reaction temperature 190 °C (calculated according to Arrhenius equation) guaranteed complete decomposition of L101 upon reaction period 6 min. Grafted IAH onto PLA backbone was proved by infrared spectroscopy (FTIR). Structure analysis also proved IAH isomerization to citraconic anhydride (CAH) which affects monomer reactivity at processing temperature. Homopolymerization of IAH was predicted regarding thermal stability of extracted byproducts compared to poly(itaconic anhydride) (PIAH) prepared by radical polymerization in solution. Acid–base titration proved that amount of grafted IAH increases with increasing IAH and L101 concentrations. However, increasing IAH and L101 concentrations lead to higher extent of undesired reactions which were detected by melt flow rate measuring (MFR).

Simplified scheme illustrating PLA grafting with itaconic anhydride initiated by free radicals in melt.Figure optionsDownload as PowerPoint slide