Effect of composition drift on emulsion copolymerization rate

With K2S2O8 initiator and Na dodecyl sulfate emulsifier, batch emulsion copolymn. rates of styrene (I) and Me acrylate (II) are investigated at different monomer or monomer/water ratios at 50 Deg. The compn. drift occurring during the copolymn. is detd. by reactivity ratios and monomer partitioning between the various phases present in the emulsion system. Monomer partitioning studies show that the monomer ratio in the latex particles is the same as that in the droplets, although the total monomer swellability of the (co)polymer latex particles depends upon copolymer and monomer droplet compn. In absence of monomer droplets the equil. monomer concn. in the aq. phase is closer to its satn. value, i.e. water soly., than the monomer concn. in the latex particles. Due to compn. drift, the kinetic behavior differs widely from the homopolymns. depending on the initial monomer ratio. The copolymn. rate strongly varies during copolymn., giving a conversion-time plot differing in shape from the sigmoidal shape usually obsd. in emulsion homopolymn. The penultimate effect in I-II copolymn. is responsible for the changes, as indicated by conversion-dependence of the copolymn. rate during batch emulsion copolymns. starting from an I-rich monomer feed, leading to a strong compn. drif