Propagation constant, variation with conversion

Efficiency of Intermediate Formation. The variation of the efficiency of a primary intermediate with conversion of the feed hydrocarbon can be calculated (22). Ratios of the propagation rate constants ( 2 / i) reactor type (batch or plug-flow vs back-mixed) are important parameters. 

Very similar variations in average copolymer composition with conversion have recently been observed in the styrene methyl methacrylate system by both Johnson et al ( and by Dionisio and O Driscoll (. The reason for the variation may be due to a viscosity effect on propagation rate constants QO). 

Figure 4. Styrene emulsion polymerization—variation of the propagation constant with conversion during adiabatic polymerization of 395-A latex particles (kp values normalized to 75 °C with an activation energy of 7700 cal/gmol and in L/mol s)...

Goebel et al. [88] have found that the particle concentration decreases with conversion and the decrease is inversely proportional to emulsifier concentration. The surface tension parallels the number of particles and both abruptly increase with conversion up to 10% conversion. The higher the emulsifier concentration, the higher the number of particles which are observed. Keeping a constant concentration of emulsifier, the number of particles decreases with increasing monomer concentration. When the monomer pressure decreased by one third, the number of particles increased twice. This was ascribed to variation of the emulsifier adsorption activity with the monomer pressure. The particle concentration remains constant if the small amount of inhibitor is added. The growth of polymer particles was reported to proceed by the propagation of monomer as well as by the association of polymer particles. 

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