Abstract
Low volatility chain transfer agents such as n‐dodecanethiol (n‐DDT) are important for controlling molecular weight in the production of polymers containing styrene. The high reactivity of n‐DDT towards the styrenic radical, coupled with its low solubility in the aqueous phase, often leads to conditions of diffusion limited chain transfer in which the transport rate of n‐DDT from the monomer droplets to the polymerizing particles is inadequate to maintain equilibrium concentration in the particles. The extent to which the particles are “starved” of n‐DDT has been studied by measuring n‐DDT consumption and molecular weight during styrene emulsion polymerizations. Varying surfactant and/or initiator concentration is shown to alter the n‐DDT consumption and the molecular weight profiles. The two‐film diffusion theory was applied to our data using monomer droplet and polymer particle measurements. Experimental data and theoretical considerations support the existence of monomer droplets beyond the expected end of Interval II for styrene emulsion polymerization.
Acknowledgment
Financial support from the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged.