Molecular mechanism of the ring-flip process in polycarbonate

Abstract

Calculations of the conformational preferences of isolated single chains of poly(2,6-dimethylphenylene oxide) (PPO) and bisphenol-A polycarbonate (PC) predict that the rings of both chains are nearly free rotors at room temperature. However, experimental dipolar rotational spin-echo 13C NMR shows that in the glass, the rings of PPO execute only small-amplitude motions while those of PC undergo primarily 180°r ing flips (a hindered rotation) superimposed on some wiggles. Geometrical considerations of the dense packing of chains in the glass suggest that the rings of adjacent chains block rotational freedom. We propose that the mobility of the PC main chain results in lattice distortions which allow ring flips not permitted by the stiffer PPO main chain.

A Robust Technique for Two-Dimensional Separation of Undistorted Chemical-Shift Anisotropy Powder Patterns in Magic-Angle-Spinning NMR

“…8d, also show indications of a broad distribution of small-and medium-amplitude motions. Again, it is known from 2 H quadrupolar and C-H dipolar spectra that all rings flip on the 100-µs timescale at ambient temperature, and that the rings undergo medium-amplitude motions (31,32). The simulation of Fig.…”

Polymer Transport Properties

“…A gas molecule is capable of executing four distinct types of diffusional jumps, depending on which of the two distinct sorption environments it is diffusing from and diffusing into (92,93). Denoting the Henry's law and Langmuir environments as D and H, respectively, the four possible jumps can be depicted as follows: …”

Comportamento dinâmico-mecânico e relaxações em polímeros e blendas poliméricas

“…A relaxação γ é a que confere um comportamento mais interessante ao PC. Após várias tentativas para a atribuição desta transição aos movimentos internos das cadeias e grupos laterais [15][16][17][18][19] , Jones 20 propôs um modelo molecular que combina movimentos intramoleculares com acoplamento intermolecular, como esquematizado na Figura 6 20 .…”