The invention relates to a copolymer and a substrate having a surface, at least one part of which is coated with an epilame agent comprising at least one compound in the form of a copolymer comprising V units, N units, optionally at least one M unit, and optionally at least one P unit, linked by covalent bonds by their main chains, wherein wherein W, X, Y, Z are spacer arms, T is a tracer group arranged to determine the concentration of epilame agent in an epilame-coating bath, L is a halogenated, preferably fluorinated, C1-C20 carbon moiety, A is a substrate anchoring moiety, Q is H, CH3, or a hydrocarbon chain different from T. The invention also concerns a method for coating such a substrate with epilame, said method comprising a step of checking the concentration of epilame agent in the epilame-coating bath by means of the tracer group and if necessary, a step of readjusting the concentration of epilame agent in the epilame-coating bath.