Improving Grafting Efficiency of Dicarboxylic Anhydride Monomer on Polylactic Acid by Manipulating Monomer Structure and Using Comonomer and Reducing Agent

Maleic anhydride (MA) grafted polylactic acid (PLA) acting as reactive compatibilizer for PLA blends and composites has been reported. However, melt free-radical grafting of MA on PLA is often subject to steric and electron effects of the substituents in the monomer and low initiation efficiency, yielding low grafting efficiency (E g). In this work, five dicarboxylic anhydride monomers, including MA, itaconic anhydride (IA), cis-1,2,3,6-tetrahydrophthalic anhydride (TA), 4-allyltrimellitate anhydride (ATA), and 4-methacryloxyethyl trimellitate anhydride (META), were grafted onto PLA, and the effect of steric hindrance on E g was assessed. It is noted that E g values followed the order of ATA > META ≫ MA ≥ TA > IA. The introduction of styrene as a comonomer selectively increased the E g values of three electron-deficient monomers, MA, IA, and META, while Sn­(Oct)2 as a reducing agent increased E g for all monomers. Both styrene and Sn­(Oct)2 exhibited a synergistic effect when used in grafting MA, IA, and META.