Phosphorescent probes in studies of secondary relaxation of amorphous polystyrene and poly(n-alkyl methacrylate)s

Phosphorescence from four aromatic ketones (xanthone, benzophenone, flavone, and 9-methoxyflavone) has been used to study secondary alpha-, beta-, and gamma-relaxation processes in polystyrene and poly(n-alkyl methacrylate)s (n-alkyl = methyl, ethyl, and butyl) in the temperature range 15-400 K. Plots of normalized phosphorescence intensity versus temperature and the respective Arrhenius curves showed changes of nonradiative deactivation efficiencies, which were attributed to polymer secondary relaxation processes. In addition to the phosphorescence emission, flavones in poly(n-alkyl methacrylate)s also exhibited fluorescence emission ascribed to the protonated moiety. The presence of these two emissions indicated a probe distribution sensing two different microenvironments: protic (fluorescent) and nonprotic (phosphorescent) sites. Protic sites reveal the existence of acidic residues copolymerized to the methacrylic polymer chains. Plots of fluorescence intensity versus temperature have been used to determine the polymer relaxation processes of these acidic domains always revealing a higher onset temperature compared to the phosphorescence emission. The influence of both the size and the shape of these probes has also been analyzed, demonstrating that small molecules (xanthone and benzophenone) are more sensitive to shorter segmental motions occurring at lower temperatures.