Thermal behavior of oligo[(ε-caprolactone)-co-δ-gluconolactone] enzymatically synthesized in reaction conditions optimized by experimental design

Abstract

The thermal behavior of co-oligomers of e-caprolactone (ECL) with gluconolactone, compared to the e-caprolactone oligomer, has been assessed by thermogravimetric analysis, while differential scanning calorimetry was used to evaluate the melting comportment. As the insertion of more hydrophilic structural units can improve the properties and functionalities of the ECL oligoesters, the enzymatic in vitro oligomerization process was optimized by a 3-factorial/3-level experimental design, using the Box–Behnken method. The selected independent variables were the temperature, the enzyme amount, and the molar ratio of monomers, while the co-oligomerization degree and the mass average molecular mass (calculated from MALDI-TOF MS data) were the response variables. The results indicate that temperature has the most significant effect and is directly correlated with the formation of linear co-oligoesters. The overall effect of the other variables was also significant. The thermogravimetric analysis of the co-oligomer synthesized in the optimized conditions indicated a decrease of the thermal stability and compared to the ECL oligomer. Thermoanalytical techniques can consistently improve the utilization efficiency of polymer-based formulations in pharmaceutical and medical applications.