shaped articles of a crosslinked poly resin can be prepared in a relatively simple process to be imparted with greatly improved resistance against heat , water , and chemicals in a much higher productivity than in the conventional electron - beam irradiation method . the method comprises the steps of compounding the resin with an organosilane compound having an ethylenically unsaturated group , e . g ., vinyl , and at least one alkoxy group in a molecule and a free - radical generator , e . g ., organic peroxides , heating the resin compound to effect graft - polymerization of the organosilane compound to the polymer molecules , shaping the resin compound into a desired form , and heating the shaped body in water containing a silanol - condensation catalyst dissolved or dispersed therein .