On the mechanism of emulsion polymerization of styrene. II. Polymerizations in soap solutions below and above the critical micelle concentration and some remarks on the kinetics of emulsion polymerization
1960; Wiley; Volume: 44; Issue: 143 Linguagem: Inglês
10.1002/pol.1960.1204414321
ISSN1542-6238
Autores Tópico(s)Innovative Microfluidic and Catalytic Techniques Innovation
ResumoAbstract Emulsion polymerizations of styrene were carried out at different phase ratios. The initial soap concentration was varied from below to above the critical micelle concentration (CMC). Above the CMC the number of particles formed agrees with values calculated from the Smith‐Ewart theory. As the soap concentration is reduced below the CMC the number of particles decreases sharply. In this concentration range the number of particles is independent of the amount of initiator but depends strongly on soap concentration. Kinetic features suggest a similarity between particle formation in these polymerizations and in homogeneous precipitation of inorganic insoluble salts. The coefficient of variation of particle diameter distribution below the CMC is about 2.5% and at high soap concentration about 15%. Bimodal distributions are obtained when the initial soap concentration is near the CMC. The initiation efficiency of persulfate is calculated from the rate and degree of polymerization and also from the number of particles formed. The efficiency increases from 0.2 to 0.6 with decreasing persulfate concentration. When the particles are smaller than about 0.12 μ, polymerization kinetics follow the Smith‐Ewart theory. Values are reported for the monomer concentration in the particles and for the constant of propagation. Larger particles exhibit a gel effect, i.e., more than one radical can coexist in a particle for a significant lenght of time. From polymerization rate data and molecular weight measurements the rate constants for the transfer reaction to monomer and for termination are calculated. The latter constant is found to be two to three orders of magnitude smaller than values obtained in solution polymerization. The difference is attributed to the high viscosity of the interior of the particles which causes the termination reaction to be diffusion‐controlled.
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