To improve the impact resistance by uniformly dispersing and including a tetraalkoxysilane and an alcohol within a polymer particle.

A tetraalkoxysilane is added to an UP resin monomer and sufficiently stirred and mixed until it is perfectly dissolved, a polymerization initiator is then added thereto to perfectly dissolve it again. The resulting mixture is suspension polymerized in an aqueous medium. The resulting polymer particle and the aqueous medium are extracted from a reactor, and the polymer particle is separated from the aqueous medium by use of a filter or a centrifugal separator. The dried polymer particle can be suitably used as dry blasta brasive blasting material as it is.