Polymer Engineering and Science, Vol.42, No.11, 2137-2145, 2002
Melting behavior, crystallization kinetics and morphology of random copolyesters of poly(2-hydroxyethoxybenzoate) with epsilon-caprolactone
The melting behavior after isothermal crystallization and the crystallization kinetics of random poly(2-hydroxyethoxybenzoate/epsilon-caprolactone) copolymers rich in 2-hydroxyethoxybenzoate units were investigated by means of differential scanning calorimetry and hot-stage optical microscopy. The observed multiple endotherms, which are commonly displayed by polyesters, were found to be influenced both by crystallization temperature and composition. By applying the Hoffman-Weeks method to the melting temperatures of isothermally crystallized samples, the equilibrium melting temperatures of the copolymers were obtained. Furthermore, isothermal crystallization kinetics was analyzed according to the Avrarni treatment. Values of the exponent n close to 3 were obtained, independently of crystallization temperature and composition, in agreement with a crystallization process originating from predeterminated nuclei and characterized by three-dimensional spherulitic growth. Space-filling banded spherulites were observed by hot-stage optical polarizing microscopy at all the crystallization temperatures explored, the band spacing being affected by both crystallization temperature and composition. As expected, the introduction of epsilon-caprolactone comonomeric units in the polymer chain of PHEBA was found to decrease its crystallization rate.