To obtain a photoresist monomer having etching resistance, heat resistance, capability to adhere to substrates, photosensitivity, and solubility in a normal alkali developing soln. by using a compd. having a norbornene or bicyclooctoene structure.

A compd. of formula I (wherein m is 1 or 2) is used in the form of copolymer contg. the compd. of formula I and a compd. of formula I (wherein R* is an acid-sensitive protective group; and l is 1 or 2). Normally, t-butyl, 2-tetrahydrofuran, 2-tetrahydropyran, ethoxyethyl, and t-butoxyethyl groups are listed as the acid-sensitive protective group R*. The copolymer is obtd. by the polymn. using a polymn. initiator or a metal catalyst. In the case of polymn. using a polymn. initiator, further addition of a comonomer (e.g. maleic anhydride or a maleimide deriv.) capable of accelerating the polymn. is pref. The mol.wt. of the copolymer is pref. 3,000-100,000.