KINETICS AND MECHANISM OF EMULSIFIER-FREE EMULSION POLYMERIZATION .3. STYRENE NONIONIC COMONOMER (2-HYDROXYETHYL METHACRYLATE) SYSTEM

The emulsifier‐free emulsion polymerizations of styrene in the presence of about 0.33–2.7% (relative to styrene) of the water soluble comonomer, 2‐hydroxyethyl methacrylate (HEMA), and of the initiator, potassium persulfate (KPS), were carried out. It was found that KPS plays a predominant role in the particle nucleation process, since the number density of polymer particles (Np) was dependent on the 0.97‐power of [KPS]. The nucleation ability of HEMA was weak, since Np was dependent only on the 0.17‐power of [HEMA]. The particle nucleation stage ceased quite early before 1% conversion, leading to nearly monodispersed polymer particles. The nucleation is suggested to be via the homogeneous nucleation mechanism. The particles grow via the core‐shell structure mechanism (shell region polymerization), since the particle size is rather large—from 1500 to 6000 Å. The amount of HEMA can affect the shell thickness and physical properties of the shell, such as the monomer swelling capacity and monomer diffusion rate. Copyright © 1990 John Wiley & Sons, Inc.