NATURE OF PLASMA-INDUCED RADICALS ON CROSS-LINKED METHACRYLIC POLYMERS STUDIED BY ELECTRON-SPIN-RESONANCE

Plasma-induced radicals of several crosslinked methacrylic polymers such as poly-(ethyleneglycol dimethacrylate) (PEDMA), poly(2-hydroxyethylmethacrylate) (PHEMA) and polymethacrylamide (PMAAm) were studied by electron spin resonance (ESR). The observed ESR spectra did not exhibit a drastic difference in the spectral feature caused by the effect of crosslinking. All the spectral features can be represented by "nine-line spectra" as a major spectral component similar to those of linear methacrylic polymers such as polymethacrylic acid (PMAA). A pronounced effect of crosslinking, however, has emerged on the specific formation in the radical structure and the stability of radicals formed, especially in PEDMA. The formation of fewer kinds of radical in PEDMA is apparently caused by the high degree of crosslinking which leads to a suppression of the occurrence of depolymerization on plasma irradiation.