Four aluminum(III) trialkoxides, namely Al(III) ethoxide (1), Al(III) isopropoxide (2), Al(III) tert-butoxide (3), and Al(III) sec.-butoxide (4), were employed as initiators for the bulk ring-opening polymerizations of δ-valerolactone (VL) and ε-caprolactone (CL). Chemical structure and properties of the prepared polymers were assessed by various techniques, such as FTIR, H-NMR, GPC, TGA and DSC. The effects of initiator concentrations and solubility as well as temperature were investigated for optimum polymerization conditions. It was found that the optimal conditions were 120 °C for 72 hours with 0.2 %mol of initiator. However, 1 and 3 only partially dissolved in the CL monomer and gave no polymerization at low initiator concentration. In contrast, 4 was completely soluble in CL monomer and gave the highest yield (92%) and molecular weight ( M n = 2.83 x 104 g/mol). Both polymers exhibited similar melting characteristics, with PCL being thermally more stable than PVL.
