Polymers that can be cleaved at predetermined sites by ionizing radiations have been synthesized by incorporating benzylic esters into their skeletons. Secondary electrons generated by ionizing radiations are captured by the benzylic esters to dissociate into benzylic radicals and carboxyl anions, so that the polymer skeletons are cleaved at predetermined sites. The T-irradiation of a three-armed star polymer, 1,2,4-tri-(2-polystyrene-2-methyl-propyonyloxymethyl)-benzene, results in the selective scission of the arms, and the resultant radicals neither combine with each other nor graft to the other polymer skeletons to give larger polymer molecules. The irradiation of poly(methyl methacrylate) crosslinked with 4-methacryloyloxybenzyl methacrylate results in the selective scission at the crosslinking sites with high radiation-chemical efficiency of 8.5 scissions per 100 eV radiation energy absorbed. These results indicate that the incorporation of benzylic esters into polymer skeletons opens a new way of constructing radiation resists with high sensitivity to ionizing radiations and high resistivity to plasma etching. (C) 2008 Wiley Periodicals, Inc.