Rotational dynamics ESR investigation of the cholestane spin probe dissolved in a narrow dispersity poly(ethyl acrylate): effect of the presence of trace amounts of free monomer

Abstract

The dynamics of cholestane spin probes dissolved in poly(ethyl acrylate) (PEA) matrices was fully investigated over a wide temperature range by means of ESR spectroscopy. A PEA sample with narrow molecular weight dispersion (PEA1) and a second one (PEA2) doped with about 2.7 wt.-% free ethyl acrylate were employed. Depending on temperature, different dynamical regimes were identified. The coupling between the spin probe dynamics and structural, β, and γ relaxation processes was recognised. At higher temperatures, Vogel-Fulcher laws well described the temperature dependence of the spin probe rotation, which tracks the backbone dynamics with different coupling degrees. The experiments provide the chance of evaluating the onset of cooperativity in the different PEA matrices. The information is obtained by comparing the temperature dependence of probe rotation with that of rheological measurements. Moreover, the dynamics of cholestane in PEA2 shows an Arrhenius regime in the highest temperature region, which exhibits a complete decoupling from the backbone dynamics. Cholestane spin probe.