Glass transition temperature of a component near infinite dilution in binary polymer blends: Determination via fluorescence spectroscopy

A study was conducted to demonstrate the use of fluorescence to yield the first direct probe of glass transition temperature (T_g) of a component near infinite dilution in a polymer blend. It was demonstrated that intrinsic fluorescence of styrene-Xblock copolymer present near infinite dilution in polyX was used to determine critical micelle concentrations below which copolymers existed as unimers in polyX. The temperature (T) dependence of fluorescence was used to measure T_g in various blends. The combined monomer and excimer fluorescence in the non-dilute blend was characteristic of a system in which polystyrene (PS) was phase separated in agreement with the immiscibility of this blend outside the near-infinite-dilution limit. The stronger T dependence in the rubbery state for the nondilute blend also agreed with studies of styrene-containing random copolymers showing that this behavior was observed in systems exhibiting excimer and monomer fluorescence.