Eco-friendly synthesis of biodegradable poly(ε-caprolactone) using L-lactic and glycolic acids as organic initiator

Biodegradable poly(ε-caprolactone) (PCL) was successfully synthesized by the green polymerization process that was conducted in the absence of heavy metal catalyst and toxic solvent. L-Lactic (LLA) and glycolic acids (GA) were utilized as green initiator for the bulk ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). These organic initiators could produce PCL with number average molecular weight (M_n) in the range of 8.46 × 10³–1.98 × 10⁴ g/mol and molecular weight distribution (MWD) of 1.71–1.81. GA could produce higher molecular weight PCL than LLA under identical synthesis condition. The catalytic performance of these initiators in the ROP of ε-CL was completely investigated by the non-isothermal differential scanning calorimetry (DSC). From non-isothermal DSC kinetics analysis, the reactivity of GA was higher than LLA in the bulk ROP of ε-CL as supported by the lower values of activation energy (E_a) and frequency factor (A) of GA than LLA initiator. The polymerization mechanism for the ROP of ε-CL initiated by LLA and GA was proposed through the activated monomer mechanism.