POLYMERIZATION OF MINIEMULSIONS PREPARED FROM POLYSTYRENE IN STYRENE SOLUTIONS .3. POTENTIAL DIFFERENCES BETWEEN MINIEMULSION DROPLETS AND POLYMER PARTICLES

In two previous papers, it was demonstrated that the addition of a sma ll amount of polystyrene to the styrene used in preparing miniemulsion s results in a substantial increase in the overall polymerization rate and the number of polymer particles formed. In this paper, this behav ior is attributed to a basic difference in the abilities of miniemulsi on droplets and polymer particles to capture aqueous phase free radica ls. It is hypothesized that miniemulsions prepared from polystyrene in styrene solutions resemble the polymer particles formed in normal (i. e., no polymer) miniemulsion polymerizations at early conversions. Thi s being the case, these polymer-containing droplets are able to effect lively compete with growing polymer particles for free radicals, where as their counterparts which contain no polymer are not, and as a resul t a greater fraction of the initial droplets become polymer particles. Based on this mechanism, it is speculated that the presence of the po lymer increases the capture efficiency of the droplets by modifying ei ther their interior (i.e., by increasing the interior viscosity, there by increasing the probability of a radical to propagate rather than ex it) or the droplet/water interface (i.e., by disrupting a SLS/CA inter facial barrier to radical entry). Experimental results are reported wh ich support the latter.