Fractionary couplings of spin probe to backbone and side group dynamics of a liquid crystal polymer

The cholestane spin probe dynamics in a nematic polymeric matrix after annealing at a temperature value slightly above the T_NI was investigated by ESR spectroscopy in a wide temperature interval. Careful lineshape analysis showed that a two δ-like distribution better represented the experimental spectra. The dependence on temperature of the population in the different sites was evaluated and compared with the analogous one previously found for the same polymer/spin probe system that had been annealed at a temperature well above the T_NI^[1]. The temperature dependence of the spinning correlation time of the spin probe rearranging in slow and fast sites led us to locate them in the backbone and side groups of the polymer. The cooperatively degree in dynamics was quantified. A signature in temperature scale at the onset of cooperativity in backbone dynamics was recognized.