Effects of temperature on styrene emulsion polymerization kinetics

The effects of temperature (T) on the kinetics of styrene emulsion polymerization with constant levels of surfactant and initiator were investigated. The production rates of the initiator radicals in water (rho(i)) increase with T, while electrolyte concentrations remain constant. The effect of ionic strength on the particle nucleation and colloidal stability of the latex particles in the course of polymerization can be eliminated. The number of latex particles (N-p) nucleated is proportional to rho(i) to the 0.27 power, which is not consistent with the Smith-Ewart Case 2 model(N(p)proportional to rho(i)(0.4)). This discrepancy is attributed ro the following: (1) particle nuclei are continuously generated beyond the Smith-Ewart Interval I, presumably due to the mixed mode of particle nucleation (micellar nucleation/homogeneous nucleation), (2) the range of the constant polymerization rare region (Smith-Ewart Interval II) becomes narrower when T increases from 50 to 80 degrees C, (3) the reaction system deviates from Smith-Ewart Case 2 kinetics due to desorption of radicals out of the particles when T> 60 degrees C. and (4) a significant population of tiny monomer droplets still remains in the reaction mixture beyond the Smith-Ewart Interval II.