Propagation constant, variation with temperature

The propagation rate constant did not depend on the monomer concentration which corresponds to the first-order propagation step. The activation energy of the propagation calculated according to the variation of Kp with temperature was found to be 6.5 0.5 kcal/mole. 

Since the rate-constants calculated by Kunitake and Takarabe for styrene contain unknown contributions from at least three propagators, they cannot be included in our final table of results. It is also evident that the variation of the rate-constants with temperature cannot provide any useful information, because the relative contributions from the different propagators change with temperature. 

Figure 3. Styrene emulsion polymerization—variation of the propagation constant with temperature during adiabatic polymerization of 395-A latex particles (kp in...

Thus, the rate of transfer with a PO monomer with a much higher activation energy varies more with the temperature than the PO propagation reaction. As an immediate consequence, by the decreasing the polymerisation temperature from 110-120 °C to 80 °C [69], polyether polyols with much lower unsaturation are obtained. In order to get convenient reaction rates, the catalyst concentration was increased. Table 4.3 shows the variation of propagation constant Kp of PO anionic polymerisation as a function of temperature. 

Taffanel used measurements of the chemical reaction rate at temperatures lower than the temperature of self-ignition, and measurements of the time of self-ignition at a higher temperature, in order to determine the dependence of the heat release rate on the temperature and concentration. Further, Taffanel introduced measurements of the flame propagation velocity. He compared experimental data with the theoretical calculation, carried out under the assumptions of a constant chemical reaction rate in the interval from Tb to Tb — 9 and the absence of chemical reaction at all lower temperatures, also ignoring the Arrhenius dependence of the reaction rate on the temperature and the variation of the concentration. 

The elementary rate constants were calculated from ratio kp/kt, obtained from the polymerization rate and initiation rate and the ratio kp/kt, estimated from the lifetime of the radical determined by the rotating sector method. The mean lifetime of the propagating radical and derived rate constants for methacrylates are shown in Tables 7—8. The variation of the propagation rate constant for methyl methacrylate with solvents is in accordance with the result obtained by Bamford et al.2 at 25 °C. Since the largest and the smallest kp value for phenyl methacrylate differ by a factor of 1.6 and for methyl methacrylate by a factor of 1.4, the estimation of the rate constants must be performed under experimental conditions in which the accumulated error is so small as to permit a distinction of the difference. Therefore, particular attention was given to the constancy of the reaction temperature ( 0.001 °C), constancy of light source, purity of monomers and solvents, and reproducibility of observed values and to the retention of the square wave in the rotat-... 

Scheme J. This scheme directly adjusts the column material balance by manipulation of the distillate flow. The main advantage of this scheme is that it has the least interaction with the eneigy balance. In terms of a McCabe-Thiele diagram, this means that the slopes of the column operating lines can be held constant in spite of energy balance upsets. This independence ftom energy balance upsets is achieved by the scheme s ability to maintain a constant internal reflux even for variations in external reflux subcooling. When the temperature of the external reflux varies, the external reflux adjustment to maintain accumulator level offsets temporary internal reflux variations. If the accumulator level loop responds rapidly, the dis-tuibanoe will not propagate down the column, and the column s overall material balance remains undisturbed.

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