PHOTOPHYSICAL STUDIES OF ISOTACTIC POLYSTYRENE IN ITS GEL STATE

Fluorescence emission spectra and decays are reported as a function of time and temperature for isotactic polystyrene in its gel state. A comparison of changes in the excimer spectra with variation of the conformational distribution based on Fourier transform infrared measurements indicates the existence of at least two different specific conformations in the gel state. The intensities of monomer and excimer emissions are time and temperature dependent and allow relaxation processes occurring within the gel matrix to be probed. Fluorescence decay and emission spectra investigated at various temperatures indicate that, below 310 K, the system is thermodynamically reversible, whereas above this temperature the system is irreversible. Three excimer structures were identified in the high-temperature spectra, and their time dependence is discussed in terms of changes in the polymer-solvent and conformational distribution of the gel structure. Time-resolved fluorescence spectra allow unambiguous identification of three separate excited-state complexes. Differences in the types of conformations that dominate in different conditions can be correlated with the form of the crystallites obtained from the gel. The time-dependent data are discussed in terms of a structured gel network capable of exhibiting conformational and reptational relaxation behavior.