Synthesis of well-defined poly(dimethylsiloxane) telechelics having nitrobenzoxadiazole fluorescent chain-ends via thiol-ene coupling
Abstract
Well-defined PDMS telechelics having nitrobenzoxadiazole (NBD) fluorescent probes covalently attached at both chain-ends were prepared in two steps and a series of fractionation procedures starting from commercially available divinyl-terminated PDMS having a broad molar mass dispersity. First, thiol-ene coupling between 6-mercapto-1-hexanol and vinyl chain-ends allowed the formation of dihydroxy-terminated PDMS telechelics through the formation of a thioether linkage. The resulting material was then sequentially fractionated using dichloromethane/methanol mixtures to afford several well-defined dihydroxy-terminated PDMS fractions having sharp distributions of molar masses (Mn = 99.5158 kDa and D < 1.2). The NBD fluorescent probes were then attached at both chain-ends by N,N'-dicyclohexylcarbodiimide/4-(dimethylamino)pyridine esterification coupling between the hydroxyl groups and 6-(7-nitrobenzofurazan-4-ylamino)hexanoic acid. The resulting fluorescent PDMS telechelics were characterized by SEC, 1H NMR, UVvisible, and fluorescence spectroscopies. These materials are suitable probes to investigate the dynamics of polymer chains in bulk or at interfaces by the fringe pattern fluorescent recovery after photobleaching technique.