STUDIES ON SPIN-LABELED POLY(NORMAL-BUTYL ISOCYANATE)

The stiff-chain polymer poly(n-butyl isocyanate) was labeled with the nitroxide 3-carbamoyl-PROXYL covalently positioned at the main-chain terminus. ESR spectra were measured as function of solvent composition and temperature using carbon tetrachloride, a good solvent, and benzene, a poor solvent. In the dry solid the nitroxide exhibits little motion up to 25 °C but rapidly gains motion and by 60 °C is motionally narrowed. Addition of small amounts of either solvent at any temperature gives rise to bimodal nitroxide relaxation times, one characteristic of the dry polymer at that temperature and the other characterizing a fast motion of 0.02-0.2-ns relaxation time. These results are correlated with side-chain motion as observed by1H NMR and known mechanical, thermal, and morphological properties of the Polymer The effect of diluent or temperature on side-chain motion has a corresponding effect on the motion of the nitroxide positioned at the end of the main chain. © 1990, American Chemical Society. All rights reserved.