Glass transition and quantum yield for fluorescent labelled polystyrene core-forming block in self-assembled nanomicelles of amphiphilic diblock copolymers

Amphiphilic fluorescent diblock copolymers containing a pyrene-labelled polystyrene (PyPS) block, PyPS-block-poly(acrylic acid) (PyPS- b -PAA) and PyPS-block-poly(ethylene oxide) (PyPS- b -PEO) were synthesized by atom transfer radical polymerization (ATRP). All resultant diblock copolymers and intermediates were characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). PyPS- b -PAA in water and PyPS- b -PEO in water or ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide ([EMIM][TFSI]) can self-assemble into spherical nanomicelles with diameters less than 100 nm. Glass transition and fluorescent quantum yield of the core-forming PyPS block confined in the self-assembled spherical nanomicelles were investigated by fluorescence spectroscopy. A dramatic reduction of glass transition temperature ( T g ) of the PyPS block within PyPS- b -PEO nanomicelles was observed relative to PS or PyPS bulk. However, in aqueous dispersions, the PyPS block within PyPS- b -PAA nanomicelles exhibited an analogous T g near to PS or PyPS bulk. Moreover, the fluorescent quantum yield of the PyPS block within the self-assembled nanomicelles in aqueous dispersions is much higher than that of PyPS- b -PEO in toluene solution as well as its bulk.