Synthesis and kinetic study of a PCL-GAP-PCL tri-block copolymer

Abstract

An energetic tri-block copolymer PCL-GAP-PCL (Mn = 1794) was synthesized by a ring-opening polymerization of ε-caprolactone with glycidyl azide polymer (GAP) of low molecular weight (Mn = 1006 g/mol) as initiator, in the presence of dibutyltin dilaurate (DBTDL) as catalyst, at 100 °C in the absence of solvent. The products obtained in high yield were characterized by FTIR, gel permeation chromatography (GPC), and 1H and 13C NMR spectroscopy. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were used to study the thermal behaviour of the polymers. An advanced isoconversional method has been applied for kinetic analysis. The activation energy, calculated by the Flynn-Wall-Ozawa (FWO) and Kissinger methods, and thermal analysis revealed that the tri-block copolymer has greater thermal stability than homopolymer GAP. The results of the activation energies from the Kissinger method for the first and second steps were 180.3 kJ·mol-1 and 209.8 kJ·mol-1, respectively. Furthermore, for the copolymer, the activation energy versus the level of conversion was calculated by the FWO method. The glass transition temperature (Tg) for GAP was influenced by the PCL blocks; as a result the copolymer (Tg = -64 °C) showed better thermal properties than homopolymer GAP (Tg = -48 °C).