The radiation-sensitive composition according to claim 2, wherein said copolymer has the general formula: ##STR13## wherein R1 is a hydrogen atom or a methyl group, R2 is a methyl group, an ethyl group, a propyl group or a butyl group, Ar is a substituted or unsubstituted phenylene group, X is --CO--, and m and n are individually an integer not less than 1.