Abstract: One aspect of the invention relates to a biocompatible medical product comprising at least 1% by weight of dry matter of a covalently cross-linked polymer that is obtained by reacting a nucleophilically activated polyoxazoline (NU-POX) with an electrophilic cross-linking agent other than an electrophilically activated polyoxazoline, said NU-POX comprising m nucleophilic groups; and said electrophilic cross-linking agent comprising n electrophilic groups, wherein the m nucleophilic groups are capable of reaction with the n electrophilic groups to form covalent bonds; wherein m?2, n?2 and m+n?5; and wherein the NU-POX comprises at least 30 oxazoline units in case the electrophilic cross-linking agent is an isocyanate. Also provided is a kit for producing the aforementioned biocompatible cross-linked polymer. The biocompatible cross-linked polymers according to the invention have excellent implant and/or sealing characteristics.