A novel functionalised poly(1-vinylpyrrolidin-2-one) (PVP) derivative, carrying a pre-determined amount of 2-(2-pyridinyldithio)ethylamine moieties as side substituents, P(VP-co-VP-SS-Py), has been prepared from carboxylated VP Polymers, in turn obtained by copolymerising 1-vinyl-pyrrolidin-2-one with 3,3-di-(ethoxycarbonyl)-1-vinylpyrrolidin-2-one in the presence of radical initiators. Using reaction solvents acting in the mean time as chain transfer agents could control its molecular weight. P(VP-co-VP-SS-Py) proved to be extremely reactive towards exchange reactions with molecules containing mercapto functions, including bioactive peptides. The exchange derivative with reduced glutathione, chosen as a model compound, was easily prepared.