MORPHOLOGICAL-CHANGES IN SEGMENTED POLYURETHANE ELASTOMERS BY VARYINGTHE NCO OH RATIO/

The morphological changes induced to segmented polyurethane elastomers by varying the NCO/OH ratio during the second step of polymerization, while keeping constant the total hard-segment content (similar to 30% ), were studied by means of Fourier transform infrared spectroscopy (F TIR), differential scanning calorimetry (DSC), and the thermally stimu lated depolarization current method (TSDC). The DSC results gave evide nce for the existence of phase separation in thermoplastic polyurethan es, whereas the elastomeric ones appeared to form a more homogeneous n etwork. The FTIR results gave additional evidence regarding phase sepa ration by detecting the strength of the hydrogen bonds. Moreover, an a ttempt was made to assess the relative contribution made to the hydrog en bonding in such systems by the two potential accepters: ester and u rethane carbonyls. The TSDC results gave a relaxation mechanism that i s due to interfacial (Maxwell-Wagner-Sillars) polarization, providing evidence of the existence of an interfacial phase. The introduced seco ndary chemical cross-links was found to affect mainly the irregularly packed hard domains and to form a more homogeneous network at higher v alues of the NCO/OH ratio. (C) 1994 John Wiley and Sons, Inc.