THE MECHANISM OF CORE SHELL INVERSION IN 2-STAGE LATEXES

In two-stage latexes where the first polymer is more hydrophilic than the second, inversion of the core and shell can occur. The mechanism of core-shell inversion during the initial and final intervals of the second-stage polymerization was investigated using model PMMA/PS systems. The phase behavior of polymer solutions intended to model the two-stage system during the initial interval of the second stage polymerization has yielded some insight into the thermodynamics of phase inversion. If the second stage monomer dissolves first stage polymer, the latter will tend to precipitate at the water/monomer interface, particularly in the presence of surfactant. The energy of the oil/water interface is thereby reduced. In the final interval, when much of the second monomer has polymerized, phase mobility is crucial to the inversion process.