SOLUTIONS AND GELS OF SPIN-LABELED POLY(OCTYL ISOCYANATE) IN NONPOLARHYDROCARBON SOLVENTS

Chain dynamics and the conformation of poly(octyl isocyanate) (POIC) i n solutions and gels have been studied by electron paramagnetic resona nce (e.p.r.) spectroscopy using a spin-labelled polymer. The polymer w as dissolved in two non-polar solvents, isooctance and cyclohexane. Th e isooctane solutions form thermoreversible gels, whereas in cyclohexa ne viscous solutions are obtained. The e.p.r. spectra were analysed as combinations of various spectral modes, one of which reflects the res triction of the label motion by the carbonyl groups in the main chain. The other modes are due to the bending of the chain, i.e. due to chai n flexibility. The temperature dependence of the chain flexibility is very different in the two solvents. Melting of the gel of POIC in isoo ctane is detected as a change from a broad immobilized e.p.r. spectrum to a motionally narrowed triplet spectrum with considerably broadened lines. Gel melting is accompanied by changes in the isotropic couplin g constant, as well as by increasing dipolar interactions between the labels in the neighbouring chains. On the other hand, the spectra meas ured from the polymer dissolved in cyclohexane change only slightly wi th temperature.