PURPOSE: To provide a copolymer useful for producing aqueous coatings improved in dyeability and in physical properties such as solvent affinity and hydrophilicity and for controlling the pore diameters of foamed polyurethanes by introducing polyoxazoline units in the main chain.

CONSTITUTION: A copolymer of formula I is obtained by introducing a polyoxazoline as segments in the main chain in the copolymer. A polyurethane, a polyester and a poly (methyloxazoline) are used for the copolymer.The copolymer is produced through a process for producing a polyoxazoline of formula II having hydroxyl groups at both the molecular ends and a process for subjecting the polyoxazoline of formula II as a diol component to a polyoxazoline reaction or a polycondensation reaction. The plyoxazoline having the hydroxyl groups at both the molecular ends is produced by reacting bisoxazoline with methyl trifluoromethane sulfonate, and subsequently polymerizing oxazoline in the presence of the obtained bisoxazolinium crystals as a catalyst in a solvent.