PURPOSE: To prevent scale formation on the wall of a polymerization vessel and, at the same time, to produce an easily handleable, large-particle size polymer, by using a specified protective colloid in producing title bead polymer by phase inversion suspension polymerization.

CONSTITUTION: As a protective colloid is used a reaction product obtained by grafting 1W20wt% α,β-unsaturated polycarboxylic acid (anhydride), e.g., meleic anhydride, onto a monoolefin polymer, MW 750W10,000, e.g., polyethylene wax, or a product obtained by oxidizing the above monoolefin polymer to an acid value of 10W100. Namely, about 0.01W10wt% above protective colloid is dispersed in a hydrophobic solvent (dispersing medium, e.g., hexane,). To this dispersion is added an aqueous solution containing a water-soluble ethylenically unsaturated monomer, e.g., acrylic acid, and a water-soluble radical polymerization initiator. Then, the resulting solution is subjected to phase inversion suspension polymerization.