| Abstract: | The effects of 9-vinyl anthracene (VAn) on solution and emulsion polymerization of styrene are examined, to gain information about the mechanism of particle formation in emulsion polymerizations. Styrene solution polymerization in ethyl benzene is found to be inhibited by small amounts of VAn. In an emulsion system, the effects of VAn are found to depend on surfactant concentration S]. With S] = 0, addition of VAn engenders some inhibition and very little change in the steady-state polymerization rate. As S] is increased from zero to above the critical micelle concentration (cmc), a slight increases in the induction period and an increasing retardation (reduction in the steady-state rate) are observed. Below the cmc, VAn has no significant effect on the particle number, but above the cmc it considerably increases the latter with concomitant appearance of very small (5–15 nm radius) particles. The data strongly support the supposition that the coagulative/homogeneous nucleation mechanism dominates particle formation for S] below the cmc. Above the cmc, the data are compatible with both the micellar entry and coagulative/homogeneous mechanisms. |
