The cationic polymerization of p-methoxystyrene (pMOS) in miniemulsion in the presence of dodecylbenzenesulfonic acid (DBSA) was studied. DBSA acts as both protonic initiator and surfactant (INISURF). The recipe was first optimized to generate stable latexes from a miniemulsion, i.e., droplets/ particles of constant size throughout the polymerization. The miniemulsion polymerization process was highly reproducible, quite fast at high temperatures (100% conversion in 8 h at 60 °C) and applicable even at high monomer content (typically 40 wt %). Poly(pMOS) of small average molar masses (≈1000 g mol -1 ) and controlled functionality were synthesized. The sharp increase in molar masses at low conversion was indebted to a decrease of water content at the interface through a cosurfactant effect. Above 20% conversion, the chain length limitation, also observed in previous ionic polymerizations in emulsion studies and referred to as critical DP, was confirmed by modeling simple kinetics. At final conversion, polymer degradation occurred as revealed by SEC, MALDI-TOF, and 1 H NMR. The particles quickly coalesced in the absence of a cosurfactant.

This paper presents the latest improvements, in terms of reactivity and molar masses, of the process of cationic polymerisation of p-methoxystyrene in miniemulsion, which was published previously [Cauvin et al., Macromolecules 2002, 35, 7919]. The formulation was adapted to change dramatically the specific surface and the polarity of the interface where the polymerisation takes place. Adding hexadecane permits to significantly decrease the particle diameter and thus to favour a faster polymerisation rate. In addition, droplets generated by sonication are ideally covered by the INISURF (initiator/surfactant) dodecylbenzenesulfonic acid and nucleate quantitatively (true miniemulsion polymerisation). Hexadecane addition finally ensures a better stability of the polymerised dispersion. A more hydrophobic acidic surfactant, though used at much smaller concentrations, again allowed increasing the polymerisation rate. Both systems, however, show no improvements in terms of molar masses compared to those observed previously. By separating the initiating agent (a super acid such as triflic acid) from the surfactant (a non-ionic one) an increase of molar masses is obtained but accompanied by an important drop of the polymerisation rate.