Formation of porous and Hollow polymer particles by urea treatment

Abstract

In this article, core/shell microspheres are synthesized by multistep seeded polymerization, using methyl methacrylate (MMA), acrylic acid (AA), divinylbenzene (DVB) and styrene (St) as raw materials. Hollow microspheres containing novel surface and inner morphology are fabricated by the process of urea post-treatment of core/shell microspheres. The morphology of microspheres is investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). On the basis of the experimental results, it is reasonable to conclude that the formation of hollow spheres is due to the reaction of ammonia which is produced by decomposition of urea, meanwhile the emission of gas makes the mesoporous shell. The results also suggested that the urea treatment time, temperature and the amount of urea are the key factors to obtain the hollow structured particles. When the urea treatment temperature was below 90°C, the microsphere morphology was nearly unchanged. The addition of ethanol could promote the formation of hollow structure. Moreover, the ratio of hollow spheres increased with increasing urea content. The optimal process to obtain hollow structured microsphere during the urea treatment is treated at 95°C for 5 h with urea mass concentration of 0.054 g/mL.