Thermal and Rheological Characterization of Polyurethanes and Their Blends Having Different Soft Segment Length

Segmented-polyurethanes (SPUs) having different soft segment length (Mn=530-3,000) and their blends were characterized by NMR, DSC and dynamic viscoelastic analyses. The SPUs were prepared from the reaction of 4,4'-diphenylmethane diisocyanate, 1,4-butanediol and polycaprolactone diol. It has been found from the DSC analysis that the long soft segment SPUs with the long hard segment have two melting points due to the hard segment while the short soft segment SPU with the short hard segment has one melting point. The dynamic viscoelastic analysis reveals that the short soft segment SPU forms a glass-like structure more easily than the long soft segment SPUs. The blends of SPUs with various composition ratios were made from the two SPUs which were different in soft segment length (Mn=530 and 2,000). DSC and viscoelastic analyses of the blends show that the short hard segment strongly affects the formation of the crystalline structure. The short segment in the blend seems to prevent the long segment from forming the long-segment-based crystalline structure, and both the segments apparently form the short-segment-based crystalline structure.