Synergistic effect of GMA and TMPTA as co-agent to adjust the branching structure of PLLA during UV-induced reactive extrusion

Abstract

In this work, glycidyl methacrylate (GMA) and trimethylol propanetriacrylate (TMPTA) are employed to adjust the branching structure of poly L-lactide acid (PLLA) during reactive extrusion induced by UV irradiation. The reaction of GMA epoxide with terminal carboxyl or hydroxyl groups at PLLA chain end can introduce C=C groups onto PLLA molecular chains. Chain branching reaction occurred via the free-radical grafting reaction of the vinyl group in TMPTA with both PLLA backbone and the C=C group terminated PLLA induced by UV irradiation. As a result, varied branching levels can be obtained by changing the ratio of GMA and TMPTA. The characterizations of rheological properties and size exclusive chromatograph correlated to the chain branches were performed to evaluate the chain branching extent. The increases in shear viscosity and storage modulus at terminal zone, and the reduced branching degree were observed in the branched PLLA samples. The results from 1H-NMR and FIRT indicate that the grafting reaction of GMA onto PLLA take place successfully. Thus, this study proposes a strategy to adjust LCB-PLA structure using GMA and TMPTA as co-agents, which is of great importance for the industrialization of PLA products.