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Special purification of the monomer and careful preparation of the reaction setup allowed a thorough study of the spontaneous thermal polymerization of methyl methacrylate over a wide range of temperatures (0–140°C). The rates of polymerization are notably lower than the few data previously reported in literature, and the degrees of polymerization slightly higher. The thermal initiation reaction is superimposed by radical production due to the natural ionising radiation (cosmic radiation etc.). This additional initiation becomes significant at temperatures below 60°C. New and more reliable monomer chain transfer constants are given.

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The viscosities of samples of poly(methy1 methacrylate), PMMA, W' tJ narrow molecular weight distributions and with molecular weights in the range 1,75 . lo4 < M , < 1,60. lo6 were measured in methyl methacrylate, MMA, as solvent at 20,40, and 60 "C in the dilute and in the semi-dilute concentration regime. By extrapolation to zero polymer concentration the limiting viscosity numbers and therefrom the Mark-Houwink-Kuhn-Sakurada parameters for PMMA in MMA were obtained. In addition, unperturbed dimensions were determined from dilute solution viscosity data. Together with some published results for more concentrated solutions of PMMA in MMA the viscosities of the semi-dilute systems were analysed in terms of scaling theories. It was found that irrespective of temperature, polymer concentration, and molecular weight all data could be quite well fitted by a single master curve when the relative viscosity q/qo was plotted as a function of the product of the intrinsic viscosity and mass concentration [q] . c.No sharp transitions between different concentration regimes were observed, however, and the scaling law exponents for the entangled solution are significantly higher than predicted by theory. 0025-1 16)

The kinetic model given by Marten and Hamielec that describes the bulk polymerization of methyl methacrylate (MMA) and accounts for diffusion‐controlled termination and propagation was modified to include termination by combination and reaction diffusion and was then tested using isothermal conversion/time and molecular weight data obtained dilatometrically at various temperatures and with three different initiators. For each series of measurements two adjustable parameters were fitted to the conversion/time data. Excellent fits were obtained and the adjustable parameters were found to be the same for all concentration levels of the three initiators and to vary in a simple manner with temperature. The predicted molecular weight averages and molecular weight distributions were in satisfactory agreement with those found experimentally considering the difficulty of measuring high molecular weight PMMA by GPC. This model thus satisfies the specifications for a polymer reactor model that can be used to optimize commercial production systems.

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The free-radical polymerization of methyl methacrylate (MMA) at very high conversions (x > 0,8) was studied in the temperature range 60°C to 160°C. 2,2'-Azodiisobutyronitrile (AIBN) and benzoyl peroxide (BPO) were used as initiators. In the case of the latter, decomposition kinetics at very high monomer conversions was investigated, too. For temperatures T 5 120°C where depropagation can be neglected a simple kinetic model based on "reaction diffusion" and free volume theory was developed. The model contains only a single adjustable parameter, the critical free volume fraction V*. Good agreement between model predictions and experiments was obtained. v* is independent of initial initiator concentration and reaction temperature, and there is some evidence that V* is also independent of the chemical nature of the initiator.

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