Crystallization and Melting Behavior of the Crystalline Soft Segment in a Shape-Memory Polyurethane Ionomer

To illustrate the crystallization properties of soft segments in shape-memory polyurethane (SMPU) ionomers, a series of SMPU ionomers with various ionic group contents and two kinds of counterions were synthesized with a prepolymerization method. An isothermal crystallization kinetic method was used to analyze the effects of ionic groups within the hard segments on the crystallization of the soft segments in a heating and cooling routine similar to that in a shape-memory function. The more ionic groups there were within the hard segments, the lower the crystallization rate was of the soft segments. The crystallization mechanism of the SMPU ionomers was quite close to that of a control sample on the basis of similar Avrami exponents; the counterion category also had some influence on the crystallization rate. Meanwhile, the melting behavior after isothermal crystallization reflected the fact that the thermal history of the hard segments had a huge effect on the crystallization mechanism of the soft segments. Especially for the SMPU ionomer quenched from 240°C, the crystallization time dependence of the secondary crystallization was rather significant, but for the SMPU ionomer quenched from 70°C, the primary crystallization of the poly(ε-caprolactone) soft segment was predominant. © 2007 Wiley Periodicals, Inc.