PURPOSE: To produce a new copolymer resin excellent in many properties as well as heat resistance.

CONSTITUTION: A bis(2-oxazoline) compound is reacted with an aromatic mercaptocarboxylic acid. Alternatively, these components are reacted with at least one compound selected from among an aromatic polyamino compound having at least two amino groups in the molecule, a polythiol compound having at least two thiol groups in the molecule, a polyepoxy compound having at least two epoxy groups in the molecule, and a polybasic acid having at least two carboxyl groups in the molecule.