ELECTRON-SPIN-RESONANCE STUDY OF FREE-RADICAL FORMATION AND ITS DECAY OF PLASMA-IRRADIATED POLY(METHACRYLIC ACID) AND ITS ESTERS

The room temperature ESR spectra of the radicals in four kinds of plasma-irradiated methacrylic polymers (acrylic resins), poly(methacrylic acid) (PMAA), its methyl ester (PMMA), and two types of their copolymers, were first studied. All the observed spectra were different from each other. The spectra of PMAA and PMMA were superficially similar to the well-known "nine-line spectrum" of gamma-irradiated PMMA, which consists of two sets of lines, major quintet and subsidiary quartet, whereas the spectra from copolymers showed large deviation from the standard isotropic nine-line spectrum. It was found with the aid of systematic computer simulations that all the spectra were outlines of multicomponent spectra, composed of nine-line spectrum (I), doublet (II), seven-line spectrum (III), and broad singlet-like spectrum (IV). These component spectra were assigned to the terminating radical (1), midchain radical (2), monomer-derived radical (3), and immobilized dangling bond sites (4), respectively. One of the special features of the observed spectra by plasma irradiation is the formation of radicals 2 and 3, the latter radical being derived from regenerated monomer on plasma irradiation followed by hydrogen additions. The concurrent formation of these types of radicals, 2 and 3, besides the terminating radical (1) is the first experimental evidence on any type of radiation-induced methacrylic polymers and may be characteristic of plasma irradiation.