Facile synthesis of monodisperse poly(styrene-co-acrylonitrile) microspheres using redox initiator in ethanol/water: Special formation mechanism

Abstract

Monodisperse poly(styrene-co-acrylonitrile) (poly(St-co-AN)) microspheres are synthesized by precipitation polymerization in ethanol/water using redox initiator under mild conditions. The microspheres have a core-shell structure with the PSt-rich core and the PAN-rich shell. The formation process shows many differences in a typical precipitation polymerization. The particles form in a short time of less than 15 min. The increase in initiator concentration leads to the increase in monomer conversion and the microsphere size. The increased water content in the ethanol/water mixed solvent controls the surface morphology of the microspheres from smooth to rambutan-like surface, due to the enhanced polarity and hydrogen bond interactions of the mixed solvent. Mechanism is analyzed by the detailed investigation on the influences of preparation parameters on the microspheres. It is confirmed that there exists two phases, say monomer droplets and continuous phase, in the reaction system. The initiation took place in the continuous phase, while the formation and growth of the microspheres occurred in the droplets. PAN segments can serve as the stabilizer in the system.