Establishing mechanisms for emulsion polymerizations

Emulsion polymerization systems are so complex that different workers often believe contradictory mechanisms for ostensibly the same system. A number of case studies are examined wherein data have been obtained that are able to refute mechanistic postulates (as distinct from supporting a mechanism by showing that a mathematical model incorporating it is able to reproduce a limited range of data). These examples are: (1) particle nucleation (refutation of micellar entry); (2) free radical desorption (refuting its unimportance for systems with insoluble monomers, and showing that the transfer/diffusion mechanism for this process is suspect); (3) entry (refutation of 100% initiator efficiency); (4) propagation (refutation of the assumption that the propagation rate coefficient (k p ) drops to zero at the glass transition); and (5) termination (refutation of the assumption that dependence on lengths of each chain can always be ignored).