Emulsion polymerization of styrene. Use of n-nonyl mercaptan for molecularweight control

The unseeded emulsion polymerization of styrene with n-nonyl mercaptan (nNM ) as chain transfer agent (CTA) was investigated, with the aim of producing a PS latex of a low molecular weight polydispersity at high conversion and in short reaction times. To this effect, starved and minimum time semibatc h reactions were investigated and compared to equivalent batch polymerizati ons. The high reactivity of nNM with respect to the monomer makes it feasib le to implement a minimum time policy with intermediate addition of CTA onl y. The MWDs of the minimum time runs were intermediate between the broader distributions of the batch reactions and the narrower distributions of the starved experiments. The conversion profiles of minimum time experiments al most coincided with those of equivalent batch polymerizations. For controll ing MWDs through semibatch operations, it seems preferable to use nNM inste ad of other (less reactive and more common) CTAs like tert-dodecyl mercapta n or CCl4. (C) 2001 Elsevier Science Ltd. All rights reserved.