Example 25
A dispersion comprising 246 parts of water, 26.8 parts of 50 wt. % surface-modified colloidal silica (Levasil, particle size 60 nm surface-modified with 40% propylsilyl/60% glycerolpropylsilyl) was prepared and maintained at a pH of approx. 4.5. The aqueous dispersion was mixed with an organic phase that contained 2.0 parts of dilauroyl peroxide, 27 parts of isopentane and 0.3 parts of trimethylolpropane trimethacrylate. Acrylonitrile (AN) and α-methylene-γ-butyrolactone (MBL) were added in the amounts as indicated in Table 5. Polymerization was performed at 62° C. in a sealed reactor under agitation during 20 hours. After cooling to room temperature a sample of the obtained microsphere slurry was removed for determination of the particle size distribution. After filtration, washing and drying the particles were analysed by TMA. The dry particles contained about 17 wt. % of isopentane. The TMA-results and particle sizes are found in Table 5.
