Molecular structure design and epoxy functional modification of star-shaped poly(lactic acid) by a melt polycondensation strategy

The preparation of polylactic acid (PLA) by melt polycondensation has received increasing attention due to its simple process and lower cost. However, the low molecular weight of PLA prepared through melt polycondensation limits its application range. The introduction of branched structures and active groups into PLA has emerged as an important means to expand its application. In this study, pentaerythritol and sorbitol were used as core molecules for melt polycondensation with l-lactic acid. The effect of reaction parameters on the viscosity average molecular weight of two types of star-shaped PLA was studied. The branched structure of PLA was characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the effects of branch chain length and number on the rheological and crystallization behavior of PLA were further analyzed. The star-shaped PLA was solution-grafted with allyl glycidyl ether, which is flexible and difficult to self-polymerize, resulting in the preparation of epoxy-functionalized star-shaped PLA with an epoxy value of 0.293 mol/100 g and gel content of 5.15%. This material is expected to find applications in environmentally friendly epoxy coatings, adhesives, and special compatibilizers for PLA, and to address the problems of difficult degradation and nonrecycling of thermosetting epoxy resin. PET and SB were used as core molecules for melt polycondensation with LA. The 6PLAs was solution-grafted with AGE, which is flexible and difficult to self-polymerize, resulting in the preparation of 6PLAs-g-AGE with an epoxy value of 0.293 mol/100 g.