engleski

Study of Slow Molecular Motion of Spin Probes in Polymers by the Double-Modulation ESR Method

The slow molecular motion of a spin probe dispersed in a polystyrene (PS), poly(α-methylstyrene) (PαMS), poly(4-vinylpyridine) (P4VP), and poly(methyl methacrylate) (PMMA) matrix has been studied by the double-modulation ESR (DMESR) method. The rotational correlation times determined as a function of temperature reveal two (PS, PaMS, and P4VP) and three (PMMA) discrete motional regions. The position of crossover points between 190 and 200 K is affected very little by the structure and molecular weight of the polymer and is attributed to the temperature at which rotational motion of the spin probe skeleton takes place. Above this internal probe transition the DMESR spectra undergo a rapid line broadening in accordance with increase of temperature. Discrete molecular motions above 200 K and the corresponding effective activation energies reflect a considerable influence of the host polymer on the spin probe motion. It was concluded that the probe rotational motion responds to the side-chain motion and that the effect of these local motions is more pronounced in the matrix of higher local density. It was also shown that the DMESR method can depict a coupling of end or side-chain methyl group motions with the methyl groups of the perdeuterated spin probe below the internal probe transition.

double modulation EDR ; spin probe ; slow motions ; polystyrene (PS) ; poly(α-methylstyrene) (PMS) ; poly(4-vinylpyridine) (P4VP) ; poly(methyl-methacrylate) (PMMA)

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