STUDY OF IRRADIATED POLYMERS USING DOUBLE-MODULATION ELECTRON-SPIN-RESONANCE AND SIZE-EXCLUSION CHROMATOGRAPHY

Irradiated polymers such as polystyrene (PS), poly(methyl methacrylate ) (PMMA) and poly(alpha-methylstyrene) (PalphaMS) have been studied us ing 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 i n 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-mot ion region have been used to investigate the heterogeneity of the poly mer matrix introduced by changes in crosslinking or by degradation. Di screte molecular motions of a spin probe above the internal probe tran sition (almost-equal-to 190 K) are very sensitive to local matrix dens ity and to side-chain relaxation modes. The d.m.e.s.r. spectra indicat e clearly a bimodal motion of spin probes located in regions of two co nsiderably different crosslink densities of the PS matrix irradiated i n solution.