SOLUTIONS AND GELS OF SPIN-LABELLED POLY(OCTYL ISOCYANATE) IN NON-POLAR HYDROCARBON SOLVENTS

摘要

Chain dynamics and the conformation of poly(octyl isocyanate) (POIC) in solutions and gels have been studied by electron paramagnetic resonance (e.p.r.) spectroscopy using a spin-labelled polymer. The polymer was dissolved in two non-polar solvents, isooctance and cyclohexane. The isooctane solutions form thermoreversible gels, whereas in cyclohexane viscous solutions are obtained. The e.p.r. spectra were analysed as combinations of various spectral modes, one of which reflects the restriction 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 chain flexibility. The temperature dependence of the chain flexibility is very different in the two solvents. Melting of the gel of POIC in isooctane 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 coupling constant, as well as by increasing dipolar interactions between the labels in the neighbouring chains. On the other hand, the spectra measured from the polymer dissolved in cyclohexane change only slightly with temperature. [References: 15]