Influence of Ionic Groups on the Crystallization and Melting Behavior of Segmented Polyurethane Ionomers

The isothermal crystallization kinetics and melting behavior of the soft segment in polyurethane (PU) ionomer/nonionomer based on PCL-4000 (poly(ε-caprolactone)) were investigated using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). In general, the presence of ionic groups in PU ionomers can promote the formation of a more stable crystalline structure and lower the equilibrium melting temperature of the crystallizable phase. Comparison between the crystallization characteristics of PU nonionomers and ionomers suggests that the Coulombic Forces between ionic groups within hard segment can increase the crystallization rate and decrease the crystal size of soft segment when the total molecular weight (M_w of PU ionomer is higher than ∼71,000. On the other hand, the opposite effect of ionic groups on the crystallization rate is observed in PU ionomers with M_w below ∼20,000. The DSC thermograms illustrate that the ionic groups can significantly enhance the microphase separation in PU ionomers with higher M_w values. By the control and manipulation of crystallization and microstructure formation in PU ionomer, it is possible to achieve shape memory PUs with superior physical property. © 2006 Wiley Periodicals, Inc.