On the key role of the interface in the cationic polymerisation of p-methoxystyrene in miniemulsion

Abstract

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.

Use of a Lewis Acid Surfactant Combined Catalyst in Cationic Polymerization in Miniemulsion: Apparent and Hidden Initiators

“…The authors explained this stability by the formation of small oligomers through rapid initiation by DBSA, as soon as the system is ultrasonicated, thus acting as hydrophobes and suppressing Ostwald ripening. In an other study, adding hexadecane enabled the same authors 18 to significantly decrease the particle diameter and thus favor a faster polymerization rate. In our case, the initiatior pMOS-HCl is post-added.…”

“…Some other studies were also performed in the same vein with phosphonic acids instead of sulfonic acids. 16 Cauvin et al 17,18 recently showed that, using dodecylbenzenesulfonic acid (DBSA) as inisurf in a miniemulsion process, polymerization of pMOS proceeded without the need for Yb(OTf) 3 . Although poly(pMOS) average molar mass increases with conversion, a "controlled" active center generation could not be put forward.…”

Multi‐Functional Stabilizers in Miniemulsion Polymerization

“…For ionic polymerizations, inisurfs were molecular surfactants in which the polar head was a strong acid or base [33][34][35][36]. Thus the counter ions (proton or hydroxide) were involved in the initiation of polymerization.…”

“…Consequently, the polymerization was carried out in conditions that may not be those of completely rigorous miniemulsion polymerization. Cationic polymerization of p-methoxystyrene was initiated by the use of dodecylbenzenesulfonic acid which acted as an inisurf [35,36]. The authors demonstrated that the addition of a hydrophobe could be avoided.…”

“…Stabilizers involved in miniemulsion polymerization processes have been the object of many studies because they are at the very heart of the process: they are involved in the stabilization of the droplets/particles, they are in direct contact with the reactants (monomers, initiators), they are present in V. Mittal (ed.) Miniemulsion Polymerization Technology, (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42) © Scrivener Publishing LLC rather high amounts when comparing to other polymerization processes in disperse media like emulsion or suspension and they are often retained in the final product. For all these reasons, stabilizers became rapidly an important topic in the literature on miniemulsion polymerization [1][2][3][4].…”