This article describes a methodology to prepare polyurethanes (PUs), decorated with pendant (bio)functional side groups, by polymerizing (bio)functionalized blocked diisocyanates with polyols. Caprolactam blocked lysine diisocyanate methyl ester (BLDI-OMe) was prepared in high yields, by reacting the methyl ester of lysine with carbonyl biscaprolactam. In the absence of a catalyst, the polymerization of BLDI-OMe with polycaprolactone and polytetrahydrofuran resulted in strictly linear PUs due to the high selective reactivity of the blocked isocyanates (BIs). Although the ester appeared to be less reactive, we found hydrolyzing conditions for the ester, without affecting the BIs. The free acid groups were converted into a N-hydroxysuccinimide (NHS) activated ester, which was a versatile intermediate for further functionalization. After having demonstrated that model amines were able to substitute NHS without effecting the BIs groups, the same chemistry was used to couple biotin, giving a biotin functional caprolactam blocked lysine diisocyanate. The polymerization with polyols afforded the corresponding biotin-functional PUs. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2036-2049