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7-(Dimethylamino)-1-methylquinolinium tetrafluoroborate (2), a stable color shifting mobility sensitive fluorescent probe, was employed for investigating physical aging in amorphous polymers. A linear correlation between the emission wavelength of 2 and the specific volume of the polymer was found in polycarbonate (PC) and poly(methyl methacrylate) (PMMA). The shift in emission wavelength measured during physical aging was used to calculate the temperature and time dependence of the effective relaxation time τeff, employing an age-dependent Kohlrausch−Williams−Watts (KWW) equation. From these data and by comparison with data obtained by positron annihilation spectroscopy (PALS) in PC and volume relaxation in PC and PMMA, it was concluded that the fluorescence of 2 yields reliable information on physical aging of these polymers. The fluorescence method, employing a color-shifting probe, offers opportunities for investigating physical aging in powders and semicrystalline polymers, of specific components in blends and mixtures, and in confined systems.
Berg et al. (Wed,) studied this question.