KINETIC-STUDY ON THE POLY(METHYL METHACRYLATE) SEEDED SOAPLESS EMULSION POLYMERIZATION OF STYRENE .2. KINETIC-MODEL

A seeded soapless emulsion polymerization was carried out with poly(me thyl methacrylate) (PMMA) as seeds, styrene as monomers, and potassium persulfate (K2S2O8) as the initiator to synthesize the PMMA/polystyre ne (PS) composite latex. The morphology of the latex particles was obs erved by transmission electron microscopy (TEM). It showed a core-shel l structure. A core-shell kinetic model was proposed for the seeded em usion polymerization, in which the thickness of the shell was not cons tant. An increase of the conversion would increase the thickness of th e shell. The entire course of polymerization could be divided into thr ee regions: In the first region, the propagation rate constant (K-p) a nd termination rate constant (K-t) were kept constant at constant temp erature. The kinetic data showed that the square root of polymer yield (W-p(1/2)) was proportional to the reaction time. In the second regio n, the gel effect was considered and the termination rate constant (K- t) was empirically modified. The K-t would decrease with increasing th e conversion. In the third region, both the gel effect and the glassy effect were considered; the propagation rate constant was also empiric ally modified. The prediction on the conversion and the number-average molecular weight of polymers during the seeded emusion of polymerizat ion on the basis of our core-shell kinetic model fitted well with the experimental data. (C) 1995 John Wiley and Sons, Inc.