Combined Effect of Humidity and Composition on the Molecular Mobilities of Poly(ε-caprolactone-ran-ε-caprolactam) Copolymers

Poly(epsilon-caprolactone-ran-epsilon-caprolactam) random copolymers, P(CLo-ran-CLa), were studied in a wide composition range (0 <= PCLo <= 55 wt %) and in the wet and dry states. Both crystalline and amorphous phases of the poly(ester amide)s were characterized, the first by wide-angle X-ray scattering and the latter by the thermally stimulated depolarization current technique. Only PCLa presented 3D order, i.e., gamma* and a structures, in addition to increasing lamellar thicknesses as PCLo amount rises. The amorphous phase of wet PCLa shows additionally to moisture plasticization a loss of rigidity due to the presence of PCLo units, which affects both segmental and local mobilities. Two cooperative modes are caused by the intercalated water with two different bounds (loosely, tightly), and their behavior during the drying process is the result of two competing effects, i.e., the loss of moisture and the coexistence of the PCLo segments. In the dry state the miscible amorphous phase presents a single drastic composition-dependent segmental mobility.