engleski

Study of irradiated polymers using double-modulation electron-spin-resonance and size-ecxlusion chromatography

Irradiated polymers such as polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(alpha-methylstyrene) (PalphaMS) have been studied using size exclusion chromatography and double-modulation electron spin resonance (d.m.e.s.r.). Size exclusion chromatography coupled on-line with low-angle laser light scattering and viscometry have demonstrated that PS irradiated in the solid state gives only slight increases of molecular weight and viscosity with increasing dose. When irradiated in solution, the results confirm the existence of a highly crosslinked and heterogeneous PS matrix. PMMA and PalphaMS undergo degradation at the same doses. The d.m.e.s.r. spectra of a spin probe in the slow-motion region have been used to investigate the heterogeneity of the polymer matrix introduced by changes in crosslinking or by degradation. Discrete molecular motions of a spin probe above the internal probe transition (almost-equal-to 190 K) are very sensitive to local matrix density and to side-chain relaxation modes. The d.m.e.s.r. spectra indicate clearly a bimodal motion of spin probes located in regions of two considerably different crosslink densities of the PS matrix irradiated in solution.

size exclusion chromatography ; spin probe ; double-modulation electron spin resonance ; gamma-irradiation ; polysryrene ; poly(methyl metycrylate) ; poly(alphy-methylstyrene) ; matrix heterogeneity

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