Suspended emulsion polymerization was used to prepare poly(vinyl chloride) (PVC) resin. Fine PVC particleswere formed at low polymerization conversions. The amount of fine panicles decreases as conversion increases anddisappears at conversions greater than 30%. Scanning electron micrographs show that PVC grains are composed of looselycoalesced primary particles

especially for PVC resins prepared in the presence of poly(vinyl alcohol) dispersant. The size ofprimary particles increases and porosity decreases with the increase of conversion.In view of the particle features of PVC resin

a particle formation mechanism including the formation of primary particles and grains is proposed.The formation process of primary particles includes the formation of particle nuclei

coalescence of particle nuclei to form primary particles

and growth of primary particles.PVC grains are formed by the coagulation of primary particles.The loose coalescence of primary particles is caused by the colloidal stability of primary particles and the low swelling degree of vinyl chloride in the primary particles.