Molecular Mobility in Para-Substituted Polyaryls. 3. Low-Temperature Dynamics

Abstract

The low-temperature mechanical relaxations in poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene [poly(aryl ether ether ketone, PEEK], poly(thio-1,4-phenylene) [poly(phenylene sulfide), PPS], and poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene), [poly(aryl ether sulfone), PES] are investigated. All three polymers exhibit a low-temperature γ relaxation, in the temperature range from 40 to 100 K at 1 Hz. The apparent activation energies for the γ relaxations (15−25 kJ/mol) are close to the values derived from empirical force field molecular mechanics calculations of the “crankshaft motion” in an isolated chain portion. Only polymers with a polar interaromatic bridge (PEEK and PES) exhibit another secondary β relaxation, in the temperature range from 100 to 250 K at 1 Hz. Moreover, the apparent activation energies of the β processes are significantly higher than the activation energies of the γ relaxations. Therefore, it is concluded that polar intermolecular interactions play an important role in the molecular events leading to the β relaxation, whereas the γ relaxation is due to conformational changes mostly controlled by an intramolecular energy.

Interpretation of the observed influence of mesophase structures on the ?-relaxation in side chain liquid crystal polymers

“…f bϱ is calculated from eqs. (7) and (9), with be understood in the framework of the coupling t gϱ Å 6.2 1 10 013 s, f * bϱ from experiment (see Table II Table II 38 have reached the same conclusion n independently determined by eq. (8) which reof cooperative dynamics from their mechanical relates the experimental value of the activation laxation studies of secondary relaxation in other enthalpy E* ab to the known value of E ab given by aromatic backbone polymers including poly(aryl eq.…”

“…These authors 38 have diamonds) are plotted simultaneously against n of also used the coupling model predictions to interthe SCLCPs. In contrast to the large spread of alpret their experimental data.…”

“…Continuity of the correlation function at t Å t c leads to have been obtained from NMR measurement in dilute solution of BPA-PC 35 and from theoretical the prolific relation [12][13][14][15] calculations. [36][37][38] Therefore, the value,…”

Molecular mobility of sorbitol and maltitol: A ^13C NMR and molecular dynamics approach

“…Secondary relaxations are generally attributed to simpler motions such as local conformational changes. Nevertheless, there are examples of more complex secondary relaxations [3][4][5] for which intra-and inter-molecular degrees of freedom are concerned, with a possible influence of microstructure. Above the glass transition temperature, the relaxation diagram of an undercooled liquid can exhibit either a crossover between the α relaxation and the β relaxation or a merging of α and β processes at infinite or very high temperatures [6][7][8].…”

Hydrogen dynamics in polyethersulfone: A quasielastic neutron scattering study in the high-momentum transfer region

“…Thereby we identified two motions of the phenylene rings, p-flips and small amplitude oscillations. These processes could be associated with the secondary relaxations c and d observed by relaxation techniques (dielectric [2] and mechanical [3] spectroscopies). However, the mobility of the hydrogens is to a large extent due to the fast motions taking place below %2 ps: the controversial process found in glass-forming systems in general, known as the 'fast process' (see, e.g.…”