PROBLEM TO BE SOLVED: To obtain a triaryl borane-heterocyclinc amine compound having a vinyl group and a hetero ring containing nitrogen atoms which is useful as an underwater anti-forming agent and a (co)polymer thereof. SOLUTION: A copolymer of the present invention contains structure units represented by formula I and II (wherein R1 and R2 are each H, a lower alkyl or a lower alkenyl; R5 is H or a lower alkyl; and a structure represented by formula III is a heterocyclic amine having 5- or 6-membered ring having 1 to 3 nitrogen atoms). A compound represented by formula I is obtained by solubilizing an amine represented by formula IV and a triarylborane in an organic solvent from which oxygen is completely removed, mixing and stirring the mixture at 20 to 60 deg.C in the existence of an inert gas such as nitrogen and the like for 30 minutes to 2 days. A copolymer is obtained by copolymerizing the amine represented by formula IV and an unsaturated monomer having a radially polymerizable double bond followed by reacting the triarylborane represented by formula V with the copolymer or by copolymerizing the compound represented by formula I and the unsaturated monomer having the radically polymerizable double bond.
