Propagation rate coefficients from electron spin resonance studies of the emulsion polymerization of methyl methacrylate

The first results are reported for the quantitative application of ESR spectroscopy to emulsion polymerization kinetics. When this technique, in conjunction with dilatometric rate measurements, was applied to the seeded emulsion polymerization of methyl methacrylate at 50 °C, the dependence of the propagation rate coefficient (k) on the weight fraction of polymer (W) was found to be k = k° (0.33 ≤ w≤ 0.84) and k exp{-29.8[w - 0.84]} (0.84 ≤ w≤ 0.99), where k° = 790 ± 300 dmmol s. These results reflect the passage of the latex particles through their glass transition point (at w= 0.84), leading to the propagation step being controlled by the diffusion of monomer to the propagation site. The observed decrease in kfor w> 0.84 appears to be less dramatic than that predicted by current free volume theories