C-13 NMR INVESTIGATION OF A POLY(URETHANE-UREA) SYSTEM

A series of solid-state C-13 NMR relaxation experiments was performed on a polyether-poly-(urethane-urea) (Biomer) known to possess a microphase-separated morphology. A primary goal was to differentiate between urethane linkages which may be found at the hard segment-soft segment microdomain interface and those dissolved in the soft-segment matrix. T1(C) and T1-(rho)(H) measurements can distinguish between the hard-segment and the soft-segment carbons, but not the interfacial region between them. However, differences in the T1-(rho)(C) behavior for the urea and urethane carbonyl carbons were found, suggesting that the interfacial and dissolved hard segments can be observed by T1(rho)(C) but not by T1(rho)(H) or T1(C). Cross-polarization dipolar-dephasing experiments, in conjunction with T1(C) analysis, indicate that approximately 50% of the hard-segment rings in the sample are able to move as free rotors, without significant hindrance to motion.