A mechanism of grain formation in vinyl chloride suspension polymerization is proposed. By agitation
the liquid vinyl chloride is suspended in water as small droplets (the diameters of the small droplets are about 1 μ) in which the polymerization takes place. The small droplets agglomerated to the grains (the dianeters of the grains are about 100 μ) at about 25% conversion.Correctness of the mechanism is proved by using electron micrograph and by adopting reference data of specific surface of the resin.