Steady-state and pulsed studies of the radiation-induced polymerization of methyl methacrylate

Abstract

In order to quantify our fluorogenic molecular probe studies on the radiation-induced polymerization of methyl methacrylate (MMA), measurements have been made of the monomer conversion, CM, and polymer molecular weight distribution as a function of dose for bulk MMA polymerized by steady-state (60Co γ-rays) and nanosecond-pulsed (3 MeV electrons) radiation. In all cases, CM was found to increase close to linearly with dose up to ca. 30%. Above this conversion, autoacceleration of polymerization (the gel or Trommsdorff effect) occurs in the γ-irradiated samples. From the low-conversion steady-state data, using dose-rates of 0.21 and 2.7 Gy/s, the parameter 〈kp〉 2G(R.)/2〈kt〉 = 0.011 and 0.015 lmol-1 s-1 (100 eV)-1 respectively have been determined (with 〈kp〉 and 〈kt〉 the average rate coefficients for bimolecular propagation and termination respectively, and G(R.) the yield of the chain-initiating free radicals per 100 eV (G = 1 (100 eV)-1 0.1036 μ mol J-1)). From the 5 Hz repetitive pulse data the value of 〈kp〉 G(R.) = 1700 lmol-1 s-1 (100 eV)-1 has been determined. Taking 〈kp〉 = 342 lmol-1 s-1 from the literature results in G(R.) = 5.0 (100 eV)-1 and 〈kt〉 = 2.7 × 107 lmol-1 s-1.