Polymer drying. V. Intramolecular‐rotor fluorescence studies of evaporation from liquid‐saturated poly(styrene‐co‐divinylbenzene)

The fluorescence intensity and residual weight of poly(styrene‐co‐divinylbenzene) saturated with a < 0.003 M solution of a intramolecular‐rotor‐fluorescent probe‐molecule in a volatile liquid were monitored simultaneously as the system evaporated at 23°C to virtual dryness. The “breakpoints” in the pattern for fluorescence increase coincided with the “breakpoints” in the kinetics of desorption with respect to the number, α t of residual sorbed volatile molecules per phenyl group in the polymer, showing that both time‐studies reflect the same physical changes in the system that occur reproducibly as α t decreases monotonically through α′ s and α′ g the compositions that signal respectively incipient elimination of volatile molecules immobilized by ad sorption to polymer, and incipient transition of the system from the rubbery state to the glassy state. The fluorescence intensity attained its asymptotic limit before α t became equal to α g the composition identified earlier to be that which marks completion of the transition to the glassy state.