MOLECULAR-DYNAMICS AND MORPHOLOGY OF POLYETHER-POLYURETHANE ELASTOMERS UNDER EXTENSION BY C-13 MAS-NMR

The C-13 NMR spectra and relaxation times of Lycra 146, a segmented copolymer of a poly-(tetramethylene glycol) (polyTMG) chain extended with 4,4'-methylenebis(phenyl isocyanate) (MDI) and MDI linked with ethylene glycol were examined as a function of extension. A novel method of spooling the long yarns and spinning them at 5 kHz in a magic angle spinning NMR probe allowed examination of both "soft" and "hard" segment mobilities and estimation of respective fractions of domains. The characteristic times for cross polarization (T(CH)), rotating-frame relaxation (T1-rho(H)), and dipolar dephasing (T2*) were sensitive to even moderate extension. T1H and T1C changed only at extreme extension, with the latter exhibiting multicomponent decay. The results are interpreted in terms of crystalline and amorphous domain sizes and the relative amounts of each. The fraction of rigid MDI was found to be lower than the fraction of MDI in the hard segments, indicating incomplete phase separation or at least significant interpenetration of phases.