Orthogonal modification of polymer chain-ends via sequential nitrile oxide-alkyne and azide-alkyne Huisgen cycloadditions

The alpha- and omega-chain-ends of well-defined polystyrene chains were functionalized using consecutive Huisgen cycloadditions. Firstly, an alpha-alkyne, omega-azido heterotelechelic polystyrene precursor was synthesized in three steps: (i) atom transfer radical polymerization in the presence of (1,1,1-trimethylsilyl)-2-propynyl 2-bromo-2-isobutyrate, (ii) deprotection of the alkyne function of the initiator and (iii) nucleophilic substitution of the bromine chain-end of the polymer with sodium azide. Afterwards, the chain-ends of the polymer were modified by successive nitrile oxide-alkyne cycloaddition (NOAC) and copper-catalyzed azide-alkyne cycloaddition (CuAAC). 2 Model building blocks were tested for NOAC, while 4 building blocks were studied for CuAAC. In all cases, the orthogonal combination of NOAC and CuAAC allowed the preparation of tailored heterotelechelic polymers.