PRODUCTION OF MICRON-SIZE MONODISPERSE POLYMER PARTICLES BY SEEDED POLYMERIZATION UTILIZING DYNAMIC SWELLING METHOD WITH COOLING PROCESS

Monodisperse polystyrene particles (6.6 mum diameter) were produced by seeded polymerization utilizing the dynamic swelling method with cooling process as follows. Monodisperse polystyrene seed particles (1.8 mum diameter) were dispersed in ethanol/water (3/4 w/w) medium containing styrene monomer, benzoyl peroxide as initiator and poly(vinyl alcohol) as stabilizer at 65-degrees-C. By lowering the temperature to -5-degrees-C at a speed of -1-degrees-C/min the polystyrene seed particles were swollen from 1.8 to 7.7 mum by the absorption of styrene monomer, keeping the high monodispersity. An appropriate amount of water was then added to the dispersion at -5-degrees-C to depress the redissolution of styrene from the swollen particles into the medium. By elevating the temperature the seeded polymerization was carried out at 70-degrees-C. The production of submicron-size polystyrene new particles as a by-product was depressed by the addition of NaNO2 to the medium.