Effects of temperature on styrene emulsion polymerization kinetics

The effects of temperature (T) on the kinetics of styrene emulsion polymeri zation with constant levels of surfactant and initiator were investigated. The production rates of the initiator radicals in water (rho(i)) increase w ith T, while electrolyte concentrations remain constant. The effect of ioni c 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)proportiona l to rho(i)(0.4)). This discrepancy is attributed ro the following: (1) par ticle nuclei are continuously generated beyond the Smith-Ewart Interval I, presumably due to the mixed mode of particle nucleation (micellar nucleatio n/homogeneous nucleation), (2) the range of the constant polymerization rar e region (Smith-Ewart Interval II) becomes narrower when T increases from 5 0 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 deg rees C. and (4) a significant population of tiny monomer droplets still rem ains in the reaction mixture beyond the Smith-Ewart Interval II.