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, C _M, 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, C _M 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 〈k _p〉 ² G(R^.)/2〈k _t〉 = 0.011 and 0.015 lmol^-1 s^-1 (100 eV)^-1 respectively have been determined (with 〈k _p〉 and 〈k _t〉 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 〈k _p〉 G(R^.) = 1700 lmol^-1 s^-1 (100 eV)^-1 has been determined. Taking 〈k _p〉 = 342 lmol^-1 s^-1 from the literature results in G(R^.) = 5.0 (100 eV)^-1 and 〈k _t〉 = 2.7 × 10⁷ lmol^-1 s^-1.