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

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 ((CO)-C-60 gamma -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 gamma -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 l mol(-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 mu molJ(-1))). From the 5 Hz repetitive pulse data the value of (k(p))G(R-.) = 1700 l mol(-1) s(-1) (100 ev)(-1) has been determined. Taking (k(p)) = 342 l mol(-1) s(-1) from the literature results in G(R-.) = 5.0 (100 eV)(-1) and (k(t)) = 2.7 x 10(7) l mol(-1) s(-1).