Phenylene motion in polycarbonate and polycarbonate/additive mixtures

Abstract

Pulsed deuteron NMR line shapes have been analysed to characterize type and time scale of the phenylene group motion in glassy bisphenol-A polycarbonate. The motional mechanism involves ~z-flips about the CIC4 axis augmented by small angle fulctuations about the same axis, reaching arms amplitude of _+ 35 ~ at 380 K. The distribution of correlation times for the n-flips is heterogeneous in nature and can be described either by a log-Gaussian or an asymmetric distribution with a more rapid decay at high correlation times comparable to the Williams-Watts distribution. From both distributions essentailly the same mean activation energy of 37 kJ/mol is obtained, whereas the temperature dependent width of the highly asymmetric distribution is somewhat smaller compared to the log-Gaussian distribution. Time scale and activation energy of the n-flip motion are correlated to secondary mechanical relaxations. Low molecular mass additives, which suppress the mechanical relaxation, also hinder the phenylene motion for a substantial fraction of phenylene groups. The effect of additives is not only to shift the mean value of the distribution of correlation times to higher values but also to increase drastically the width of the distribution. The results of this work strongly suggest that the secondary mechanical relaxation and the large amplitude motions of the phenylene groups in polycarbonate are related.

Dynamic Behavior of the Minority Phase of Photoaddressable Block Copolymers

“…In the case of polymers with phenyl or phenylene side groups, 180 8 jumps around the local C 2 axis are expected and are actually found in many polymers. [46,48] These fast two-site jumps of the C-2 H bonds of the phenyl ring lead to a powder spectrum different from the Pake form. The asymmetry parameter h of the electric-field gradient determining the interaction with the electric quadrupole moment of the deuteron and, thus, the 2 H NMR spectrum is no longer zero.…”

The NMR-WEBLAB: An internet approach to NMR lineshape analysis

“…As a first example, we want to investigate the motion of phenylene groups around their C2-axes. This motional process is often met in practice and manifests itself particularly clearly in Z H NMR spectra [12,23]. Varying the flip angle within these values will not lead to any change in the total width of the spectrum.…”

Effects of Various Types of Molecular Dynamics on 1D and 2D 2H NMR Studied by Random Walk Simulations

“…If the echo delay is set to 20 s a spectrum is found in which no effects of the considered motion can be recognized, although is chosen right in the time window of 1D NMR. This indicates that highly restricted dynamics cannot be observed in 1D spectra recorded in the ordinary way using small echo delays, as is well known from other investigations (9). However, applying larger echo delays, changes in the lineshape appear which are more pronounced the larger t p as is clearly seen in Fig.…”

“…Concerning 1D spectra, rotational jumps occurring about a single axis and among a small number of sites were mainly under investigation, e.g., flips (3,4) or 2/3 (5) and 2/5 jumps (6). Sometimes, small angle fluctuations about the jump axis (7)(8)(9) or a wobbling of the axis itself (10) were additionally taken into account. In the early days of 2D 2 H NMR, similar kinds of motion were considered (11)(12)(13)(14)(15).…”