Transurfs, emulsion polymerization

Inisurfs, Transurfs and Surfmers may be used to reduce/avoid the use of conventional surfactants in emulsion polymerization. However, when Inisurfs and Transurfs are used, the stability of the system cannot be adjusted without affecting either the polymerization rate (Inisurfs) or the molecular weight distribution (Transurfs). Furthermore, the efficiency rate of Inisurfs is low due to the cage effect. It is therefore not obvious yet that these classes will become commercially significant. 

Polymerizable surfactants capable of working as transfer agents include thiosulfonates, thioalkoxylates and methyl methacrylate dimer/trimer surfactants. Thioalkoxylates with 17-90 ethylene oxide units were produced from ethoxylated 11 bromo-undecanol by replacing the bromine with a thiol group via the thiazonium salt route [8]. In the presence of water-soluble azo initiator the thio ended Transurfs (used at a concentration above the CMC) gave monodispersed latex particles in emulsion polymerization of styrene. However, the incorporation of the Transurf remained low, irrespective of the process used for the polymerization (batch, semibatch, seeded). The stability of the lattices when the surfactant and the transfer function were incorporated in the same molecule was better than when they were decoupled. 

Monteiro et al. have used a RATF Transurf in the ab initio emulsion polymerization of methyl methacrylate at 70° C. The Transurf was synthesized by esterifying a methyl methacrylate dimer with 1,10 decandiol followed by sulfonation. The authors found that only a small amount of Transurf was incorporated and suggested that, in order to increase the Transurf incorporation, the ratio of monomer to Transurf should be kept as low as possible, as achieved, e.g. in starved-feed conditions [12]. 

Monteiro, M.J., Brussels, R. and Wilkinson, T.S. (2001) Emulsion polymerization of methyl methacrylate in the presence of novel addition-fragmentation chain-transfer reactive surfactant (transurf). /. Polym. Sci., A 39,2813-20. 

ABS) and polyvinyl chloride (PVC). In the emulsion polymerization, reactive surfactants can be used as inisurfs when they can replace both the initiator and the surfactants, as transurfs when they may be used to control the molecular weight, and finally as surfmers when they are used as comonomers which are polymerizable. 

Some transfer activity is displayed by many common surfactants. For instance, when emulsion polymerization of styrene is initiated photochemi-cally using biacetyl in the presence of sodium dodecyl sulfate (SDS) as emulsifier, the resulting latex is slightly charged (3 mC/m ) with strong acid groups. Some other surfactants show more transfer activity, e.g., transurfs I and II of Table 2. 

As a first approach, a transurf prepared by esterification of the precursor surfactant with 2-phenyl-2-propenylmercaptopropionic acid has been tested. This transurf compound shows a very good incorporation in the batch emulsion polymerization of styrene, as determined by gradient polymer elution chromatography and NMR spectroscopy. 

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