Morphology of a polycarbonate in the amorphous state from molecular motion studies by broad-line nuclear magnetic resonance

Quasi-static modeling of chain dynamics in the amorphous glassy polycarbonate of 4,4'-isopropylidenediphenol

“…Visual inspection of Figures 12 and 15 also demonstrates this difference. 5. Comparison with Experiment.…”

“…The broad distribution of the energy barriers that occur in both types of simulations is in accord with the observations of several researchers who have found that NMR indicates that the distribution of the frequencies of motions is inhomogeneous and very broad.35-40 When considering the frequency distribution of the ring flip (Figure 8), it is apparent that the distribution is very broad at room temperature, covering several orders of magnitude in frequency. If the distribution is fitted to a stretched exponential function of the form40,54 m = exp (-t/rf (5) the value for /3 is between 0.1 and 0.2 for both the ring flip and the carbonate group conformational change, again indicating the extreme breadth of the distributions. The breadth of the simulated distribution is exceedingly large and leads to the finding that it is not possible to get a conclusive measure of this breadth of activation energy by experimentally simulating the structure since no experimental technique has a frequency window large enough to cover the necessary ca.…”

Dynamics of macromolecular chains in solution. A model of local motion in a polycarbonate

“…As can be seen from Tables V and VI, correlation times r2Me and r2ph are of the same order of magnitude, which suggests the possibility of the existence of a significant correlation between these motions, as previously anticipated.14,24 The observed high activation energy value for the internal rotation of methyl groups is due to the presence of two CH3 groups bound to the same carbon atom. 28 An important problem of conformational transition kinetics, assuming conformational reorientation of a single bond, consists in the recognition of the reactions of the neighboring chain fragments, discussed in the works of Helfand et al10,11,[29][30][31][32] First of all, the fact that the observed activation energy is close to the value of a single barrier may be interpreted as follows: when one bond is going through the potential barrier, all other bonds and other degrees of freedom are in equilibrium. The next direct process is the transition of the system through the reaction barrier toward equilibrium in a manner which is most favored, kinetically.…”