Alizarin Yellow R (AYR) as compatible stabilizer for miniemulsion polymerization.

HYPOTHESIS: Many solid particles have been used in Pickering stabilized (mini)emulsions. Stabilizing "particles" can be also formed in situ e.g. by aggregation of dye molecules as reported recently. Among the dyes sodium 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoate (Alizarin Yellow R, (AYR)) is one of the best stabilizers. It is assumed to act as sole stabilizer also in heterophase polymerizations and offers a great potential for applications.

EXPERIMENTS: Aqueous solutions of AYR in varying concentrations (0.3, 0.5, 1.0, 1.5, 2.0mg/mL (dye/water)) were employed as continuous phase in direct miniemulsions. The oil phase comprised ethenylbenzene (styrene) and hexadecane. The effects of AYR concentration and ultrasonication time on size and distribution of the droplets were investigated. The miniemulsions were polymerized with a water-soluble azo-initiator (2,2'-azobis[n-(2-carboxyethyl)-2-methylpropionamidine] n-hydrate, VA-057) and conversion and kinetics were determined.

FINDINGS: The AYR is successfully employed as stabilizer in Pickering-like miniemulsion polymerizations of styrene. The higher the AYR concentrations the more stable the miniemulsions, the smaller the droplet sizes and the narrower the distributions are, ranging from ca. 450 to 180nm and 0.38 to 0.15, respectively. The nucleation mechanism of the polymer particles could be revealed by the number ratio of droplets and particles and follows droplet nucleation. This is confirmed by polymerization kinetics, which is in accordance with classical miniemulsion polymerization, too.