Low-temperature radiation-assisted polymerization and the nature of active site in the methyl methacrylate-silica system

Differential scanning calorimetry and EPR and IR spectroscopies were used to study the low-temperature postradiation polymerization of methyl methacrylate (MMA) sorbed on a microporous glass (SiO₂). Sorbed MMA was found to exhibit an enhanced tendency to polymerize within a temperature range of 160–250 K. At a preliminary irradiation dose of 10 kGy, the degree of conversion of the monomer was 100%, with the fraction of homopolymer formed being within 18%. The radiation-chemical yield of radicals in the SiO₂-MMA system at 77 K was estimated at G = 53–55 per 100 eV. The paramagnetic centers formed during the low-temperature (77 K) radiolysis of SiO₂ and MMA were demonstrated to be of ionic and radical natures. The polymerization of sorbed MMA via the radical growth of polymer chains was largely initiated by ions. That the polymer synthesized forms a chemical bond with the support was demonstrated using IR spectroscopy.