Theoretical analysis of rates of emulsion polymerization

The importance of emulsion and seeded polymerizations that proceed with a small average number of free radicals per particle (n̄) has recently been recognized. We now show how to generate analytical solutions to the set of differential equations that describe polymerizations for which n is small due to the rapid transfer of reactivity from the particles. The steady state approximation is not invoked. The analysis exploits methods devised originally to describe gaseous, unimolecular decomposition reactions to which the emulsion polymerizations are analogous. As an example of their usefulness the analytical solutions are applied to the seeded polymerization of vinyl acetate. It is inferred that despite the absence of new nucleation, the efficiency of free radical capture by the particles is remarkably small (< 0.1%); possible reasons for this are discussed

The direct determination of kinetic-parameters in emulsion polymerization systems

Because of the complexity of emulsion polymerization systems, unequivocal mechanistic deductions on data on one particular aspect of the process (e. g. , particle nucleation) perforce require reliable rate parameters from other aspects (e. g. , polymerization within the particles during and after the cessation of nucleation). It is the primary aim of this work to review techniques whereby unambigous values of the appropriate rate laws and rate parameters can be obtained from experiment. The relation of this empirically determined rate law to the competing theoretical models may then properly be considered

Microscopic kinetic events in emulsion polymerization

Experimental methods are reviewed which enable the microscopic kinetic events that underpin the formation of polymer latex particles and their subsequent growth in emulsion polymerizations to be explored. The growth of latex particles is the simpler of these two processes and considerable insight has now been gained into the mechanisms of the entry of free radicals into latex particles, the exit of free radicals therefrom, the fate of the exited free radicals and bimolecular termination events in the latex particles. Some progress has been made in modelling these processes theoretically. The formation of latex particles is a more complex phenomenon. The classical picture of latex particle formation occurring by the entry of free radicals into surfactant micelles appears to lack experimental substantiation. Particle size distribution results, which contain information about the rate of production of latex particles, imply that particles are generated by a multi-step process which involves the coagulation of immature precursor particles. A semi-quantitative theory for coagulative nucleation has been developed which predicts the general features of a broad range of nucleation phenomena