PRODUCTION OF CROSSLINKED POLYMER PARTICLE

PURPOSE:To obtain the titled highly crosslinked particle having easily controllable particle diameter and useful as an assistant for toner for electrophotography, using a reaction system having excellent polymerization stability, by absorbing a polymerizable monomer in a specific seed polymer and polymerizing the monomer. CONSTITUTION:The objective particle can be produced by mixing (A) an aqueous dispersion containing (i) 1pt.wt. of seed polymer particle having a weight- average molecular weight of 500-10,000 with (B) 2-500pts. of polymerizable monomers containing (ii) >=3wt.% crosslinkable monomer and polymerizing the component B absorbed in the component (i). The amount of the component B is preferably 4-19pts. per 1pt. of the component (i). The component (i) can be produced e.g. by the emulsion polymerization process using a relatively large amount of a mercaptan-based molecular weight modifier.