Anionic Polymerization of n-Butyl Cyanoacrylate in Emulsion and Miniemulsion

Abstract

The manufacture and polymerization of stable n-butyl cyanoacrylate (BCA) miniemulsions were achieved in the presence of dodecylbenzenesulfonic acid (DBSA). This surfactant, by releasing protons at the interface, slows down the interfacial anionic polymerization of n-BCA through (reversible) termination. Preliminary emulsion experiments showed that adequate DBSA/monomer ratios and stirring rates are required to avoid the generation of long polymer chains through uncontrolled polymerization. By sonicating the original mixture to produce a miniemulsion, a fair control of oligomer generation is exerted. In all experiments, however, the final oligomer distribution is mainly composed of three to five units, with the equilibrium value imposed by interfacial polymerization/depolymerization events. As a consequence, particles quickly destabilize by Ostwald ripening of the partly water-soluble hydroxylated oligomers. Decreasing the acid content after sonication by adding hydroxide sodium permits the formation of longer chains and thus enhances particle stability. Maximum molar masses of 1200 g/mol are reached even in the latter polymerization conditions, a critical chain length for which oligomers lose their surface activity and stop propagating.

Surfactant Effect in Miniemulsion Polymerization for Biodegradable Latexes

“…In general, samples are characterized straight after dilution minimizing the effect of changes in the particle size occurring over time. However, as can be seen in Figure 10.8, the particle size and size distribution change over time, as was observed for the n-butyl cyanoacrylate/dodecylbenzenesulfonic acid miniemulsions [42].…”

“…The particle size measurements are sensitive to any variation in pH and/or acid surfactant concentration leading to chain depolymerization/ repolymerization, affecting, consequently, the particle stability [42]. In general, samples are characterized straight after dilution minimizing the effect of changes in the particle size occurring over time.…”

Macromolecular surfactants for miniemulsion polymerization

“…The reported molar masses obtained after the anionic polymerization of BCA in miniemulsion with polymeric surfactants [86] fall in the same range as those obtained following other procedures [112,128]. It is clear that in the required pH conditions, the chemical structure of the macromolecular surfactant is of primary importance for ensuring its chemical stability during the time needed for polymerization.…”

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

“…This trapped compound [12] modifies the osmotic pressure into the particles to counteract the Laplace pressure, and is called an 'osmotically' (or kinetically) stable emulsion or miniemulsion. Ostwald ripening could not be seen in any IPE systems [1][2][3][4][5], since the polymer chains that are generated through interfacial polymerisation act as this specific trapped species.…”

“…Termination reaction of course involves water, and this process may be reversible (alkyl cyanoacrylates [3,4] or episulfides [5]) or not (phenyl glycidyl ether [2] and pmethoxystyrene (pMOS) [1]). In all cases, anyway, only low molar mass oligomers are produced.…”