Crystallization studies on linear aliphatic n-polyurethanes

A detailed crystallization study of the linear n-polyurethane (n-PUR) family for n ranging from 5 to 12 was carried out by DSC supported by polarizing optical microscopy. The study embraces crystallization of all the n-PUR under both nonisothermal and isothermal conditions. The odd and even series of n-PUR defined by the parity of the number of methylenes (n) contained in the polymer repeating unit are considered and separately analyzed. All the members of the two series showed a thermal behavior consistent with their chemical constitution. Isothermal crystallization data were analyzed by the kinetics Avrami approach which revealed that the "crystallizability" of n-PUR increases steadily with the flexibility of the polyurethane chain. Melting and enthalpy temperatures of isothermally and nonisothermally crystallized n-PUR were found to vary with n according to a zig-zag plot characteristic of odd-even effect. Given the structural similitude of n-PUR with (n 2)-nylons, results were referenced to those reported for this family of polyamides.