PURPOSE: To economically and simply fix polyionene excellent in the outflow resistance to an aq. medium, antibacterial characteristics or the like and useful for a medical instrument such as an intraperitoneal tube or the like by applying a reaction product of a specific polyionene to a carrier material to crosslink the same by a crosslinking agent.

CONSTITUTION: Both reactive terminals of polyionene with a mol.wt. of 10,000-100,000 having a structure represented by formula I {wherein X is a polymn. degree; R1, R2, R3 and R4 are each a 1-4C (branched) alkyl; A and B have 6 or more carbon atoms in total and are each CH2, C2H4 or a group represented by formula II [wherein X and Y are each H, CH3, OH, CHO, NH2, NHZ (Z is a 1-4C alkyl), N(Z)2 or a group represented by formula II (wherein R', R" and R"' are H or a 1-6C alkyl) and combined to form O; (m) and (n) are 1-16]} are reacted with an excessive α,ω-difunctional compd. to obtain a reaction product, which is, in turn, dissolved in a hydrophilic solvent to be applied to an inert carrier material, and next, the reaction product is crosslinked by a crosslinking agent dissolved in an inert hydrophobic solvent to immobilize polyionene on the inert carrier material.