MOLECULAR MOBILITY IN PARASUBSTITUTED POLYARYLS .3. LOW-TEMPERATURE DYNAMICS

The low-temperature mechanical relaxations in -phenyleneoxy-1,4-phenyl ene-carbonyl-1,4-phenylene [poly(aryl ether ether ketone, PEEK], poly( thio-1,4-phenylene) [poly(phenylene sulfide), PPS], and poly(oxy-1,4-p henylenesulfonyl-1,4-phenylene), [poly(aryl ether sulfone), PES] are i nvestigated. All three polymers exhibit a low-temperature gamma relaxa tion, in the temperature range from 40 to 100 K at 1 Hz. The apparent activation energies for the gamma relaxations (15-25 kJ/mol) are close to the values derived from empirical force field molecular mechanics calculations of the ''crankshatt motion'' in an isolated chain portion . Only polymers with a polar interaromatic bridge (PEEK and PES) exhib it another secondary beta relaxation, in the temperature range from 10 0 to 250 K at 1 Hz. Moreover, the apparent activation energies of the beta processes are significantly higher than the activation energies o f the gamma relaxations. Therefore, it is concluded that polar intermo lecular interactions play an important role in the molecular events le ading to the beta relaxation, whereas the gamma relaxation is due to c onformational changes mostly controlled by an intramolecular energy.