AbstractA modified benzyloxycarbonyl (BOC) protective group, the 3,5‐di‐tert‐butyl substituted BOC (3,5‐tBBOC) group, was introduced to the stepwise synthesis of molecularly uniform oligourethanes based on 1,5‐naphthalene diisocyanate (NDI) and 1,4‐butanediol (BDO) for the protection of the amino functions of the starting material 1,5‐naphthalene‐diamine (NDA). Thetert‐butyl substituents of the 3,5‐tBBOC group significantly improved the solubility of the intermediate products in the oligourethane synthesis. Thus, applying this modified protective group, reactions could be carried out, which were not possible with the conventional BOC group, due to the insolubility of the compounds in all suitable solvents. Furthermore, the substituted BOC protective group considerably improved the efficiency of the liquid chromatographical purification of key intermediates of