Abstract: A polymerizable composition which comprises (i) a cycloolefin monomer, (ii) a metathesis polymerization catalyst, (iii) a chain transfer agent, (iv) a radical crosslinking agent, and (v) a compound (?) selected from the group consisting of compounds having alkoxyphenol structures wherein each aromatic ring has one or more substituents, compounds having aryloxyphenol structures, and compounds having catechol structures wherein each aromatic ring has two or more substituents; a thermoplastic resin composition which comprises (1) a cycloolefin thermoplastic resin, (2) a radical crosslinking agent, and (3) a compound (?); a process for the production thereof; a crosslinked resin obtained by crosslinking the thermoplastic resin composition; and crosslinked resin composite materials produced by laminating a substrate with the thermoplastic resin composition and crosslinking the thermoplastic resin composition.