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.

An extensive effort to characterize polystyrenes of a wide range of molecular weights of up to M, = 40 X lo6 by a variety of different methods is reported. The employed methods of investigation, such as frequency analyzing (dynamic) and frequency averaging (classical) light scattering, velocity sedimentation, and viscometry, always lead to linear double-logarithmic relationships between the obtained quantities and the molecular weight. Molecular weight distributions of several samples in the same molecular weight range were investigated as well by classical light scattering, velocity sedimentation, and GPC. Comparison of the results, also with fractionation data, gives good agreement between the different methods and demonstrates the usefulness of some new approaches.Until recently, synthetic polymers of extremely high molecular weights have only been of limited interest to the scientific world, even though an extension of the molecular weight scale by one or two decades might provide a crucial experimental test for some theoretical equations, e.g., relating the conformation to the excluded volume.There are, however, a number of problems associated with the investigation of the properties of extremely high molecular weight polymers: For one, the systematic preparation of such polymers requires in general a rather refined experimental technique which must meet the most stringent purity specifications, irrespective of the mode of synthesis. Anionic polymerization has been advanced systematically to yield polystyrenes in the molecular weight range of M , = 13 X lo6 with narrow molecular weight distributions (MWD).' Earlier, McIntyre et ala2 had been successful in obtaining an anionic polystyrene of M , = 44 X lo6. Emulsion polymerization just recently yielded a polystyrene of M , = 57 X lo6 after fra~tionation.~ Purely thermal polymerization of styrene at low temperatures to low conversion leads to polymers of similarly high molecular weights ( M , = 35 X lo6 ~nfractionated).~ Spontaneous thermal polymerization of methyl methacrylate at lower temperatures produces polymers in the same or possibly higher molecular weight range.5 The latter two modes of polymerization yield molecular weight distributions of M,/M,, = 2, since their molecular weights are regulated by transfer reactions to an intermediate and/or the monomer, respectively.

No abstract

Diffusion coefficients D and Ludwig‐Soret coefficients D′/D of polystyrene in toluene were determined in a convection‐free thermodiffusion cell of 1 to 4 mm. height, 100 mm. length, and at a temperature differences of 0.1 to 0.3°C. The cell had two chambers, thus allowing observation of the concentration gradient alone by optical elimination of the temperature gradient. Philpot‐Svensson and Gouy optical methods were used. Both equilibration from homogeneous concentration to Ludwig‐Soret equilibrium and from this back to homogeneous concentration lead to D and D′/D. The last method, operating with ΔT = 0 gave more exact results. It was possible to measure very low diffusion coefficients (below 10−7 cm.2sec.−1). For sharp fractions the agreement with the free diffusion is good. For broader samples the thermodiffusional D is smaller than D of free diffusion. This difference is in accordance with the different averaging of the two methods. Up to ΔT = 0.3°C. no variation of D′/D with temperature was found. The Ludwig‐Soret coefficients increase with increasing molecular weight M and decreasing concentration. The thermal diffusion coefficient D′ is nearly independent of M and shows only a very slight decline with concentration. The results of our experiments are discussed together with the work of other authors using different techniques.

ZUSAMMENFASSUNG:Es wird iiber Sedimentations-, Diffusions-und Viskositatsmessungen an Polydimethylsiloxan berichtet. Als O-Losungsmittel diente Bromcyclohexan, das bei 28 "C die Beziehung [q] = 7,8 . Mor5O liefert, sowie als gutes Losungsmittel Toluol von 25OC mit [q] = 8,28 * lo-* MoJ2 Die Reibungs-und Viskositatswerte erlauben die Berechnung des Tragheitsradius r i m O-Losungsmittel zu r o = 0,27. M112. Dieser Radius r a ist nur etwa um 40 yo grol3er als der Radius rf bei vijllig freier Drehbarkeit. Die Polydimethylsiloxankette ist folglich sehr flexibel. SUMMARY:Measurements of sedimentation, diffusion and viscosity were performed on polydimethyl-

Free-radical polymerization of methyl methacrylate in bulk at 0°C over the full range of conversion is reported. Details for stationary and non-stationary experiments are described allowing to measure both kinetically relevant ratios fk:/k, and k,/k,, f representing radical efficiency, k, rate constant of propagation and k, rate constant of termination. From these ratios the absolute rate constants k, and k, are available. The photochemical decay of the initiator 1,l'-azodicyclohexanenitrile in connection with the rotating-sector technique and observation of the post-effect after stopping the initiator decay were used. The rate of polymerization and the number-and weight-average molar masses were measured. Both, k, and k,, showed a strong dependence on conversion which is well known for k, but is reported here for the first time for k, since Hayden and Melville's determination of k, from measurements of the temperature increase during polymerization were reported.

No abstract

A dimeric biradical 'Mi plays a central role in the initiation of the spontaneous polymerization of methyl methacrylate (MI). Besides the initiation step by chain transfer reaction, a change of the multiplicity of ' M; seems to be of importance. Evidence is given by heavy atoms in the solvent or in an inert gas atmosphere, leading to an acceleration of the overall polymerization rate. The observed effect is related to the atomic number of the respective heavy atom. Measurements of the temperature dependence of the effect for carbon tetrachloride show thatas expectedno activation energy is needed for this reaction step. The results are summarized in a reaction scheme for the initiation mechanism of the spontaneous polymerization of methyl methacrylate. C-CHZ-CH CH COOCH, COOCH, 2-I COOCH, COOCH, (HI) (HHI) Part 6: cf.@. Pressent address: Kalle, Niederlassung der Hoechst AG., D-6200 Wiesbaden-Biebrich. b, Part of the dissertation of J. L., Mainz 1982.0025-1 16X/84/$03.00 *) Thiophenol is an exception, the transfer effect of which is strong as compared to the heavy **) The authors want to express their thanks to the Rohm company for the generosity in atom effect to be expected (cf. discussion in6)).supplying unstabilized monomer of extremely high purity.