Poly (l-lactic acid) synthesis using continuous microwave irradiation-simultaneous cooling method

In this study, Poly(l-lactic acid) (PLLA) synthesis was studied using direct melt condensation polymerization (DMP) method in an experimental microwave (MW) system where external cooling was applied to keep both temperature (T) and MW power (P) continuous and constant during the polymerization. T, P, reaction time (t), catalyst type, and catalyst amount were considered to determine appropriate process conditions. In addition, some experiments were carried out under the similar process conditions using MW-assisted ring opening polymerization (MW-ROP) and conventional heating (CH) methods. These methods were compared in terms of process performance and various properties of the oligomeric PLLA. According to results, polymerization rate, polymer yield, average-molecular weight, the dispersity, and thermal properties of PLLA products were similar in both MW methods but higher than CH counterparts. Furthermore, low crystallinity of PLLA products synthesized by MW methods showed the effect of MW on the optical purity (L or D) of products. Finally, energy saving was accomplished by 73% and an increase of polymer production rate by 37.7% in MW-DMP method.