Anionic polymerization of n-butyl cyanoacrylate in emulsion and miniemulsion

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.