Ring‐opening polymerization of ε‐caprolactone in the presence of dicarboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL) has been investigated in the presence of succinic acid in nitrogen atmosphere at 225°C. Analysis of the resultant polymers suggests that the poly(ε‐caprolactone) (PCL) obtained has two terminal carboxylic groups. VPO, 1H NMR and titration are used to determine the number‐average molecular weight of the PCL obtained at ε‐CL to acid molar ratios of 4, 8, 12, 14, 16 and 20, respectively. It is found that the molecular weight of the PCL is not related to the ratio of ε‐CL to succinic acid except for low ε‐CL concentrations. At a molar ratio of 14, the molecular weight of PCL reaches a maximum at a reaction time of 3 h. Beyond 3 h the ester exchange reaction becomes predominant, and the molecular weight approaches the equilibrium value (M̄e) due to the ratio of ε‐CL to succinic acid in the feed.