Poly [(4-hydroxybutyric acid)-alt-(glycolic acid)]:: Synthesis by thermal polycondensation of metal salts of 4-chlorobutyric acid carboxymethyl ester

A new sequential copolyester consisting of glycolic acid and 4-hydroxybutyric acid units was prepared by a thermal polycondensation method that uses the formation of metal chloride salts as a driving force. The polymerization conditions (time, temperature) were studied in order to obtain appropriate molecular weights and high yields. Thermal properties and thermal stability were also determined. The polymerization kinetics of sodium, potassium and cesium monomer derivatives were studied by differential scanning calorimetry and the results compared. Non-isothermal data and an isoconversional procedure (free model) were applied to determine the Arrhenius parameters (activation energy and pre-exponential factor). The kinetic model was selected according to both the Coats-Redfern method and the evaluation of isokinetic parameters.