Main-chain reorientation in polycarbonates

Abstract

romolecules, in press.Registry No. (MMA)(IB)(isoprene) (graft copolymer), 116945-20-1.

Phenylene ring dynamics in bisphenol-A-polysulfone by neutron scattering

“…It is known that phenylene rings perform -flips in several systems with characteristic times that would produce quasielastic broadening in the mesoscopic time scale at Tտ300 K. 16,18,29,32 The obtained Q dependence for the quasielastic intensity in backscattering data ͑Fig. 11͒ agrees with that which would be observed in the case of a -flip motion.…”

“…Therefore, it seems unlikely to be the origin of the secondary relaxation unless it is cooperatively linked to the motions or is part of the mechanism a͒ Electronic mail: wapcolej@sq.ehu.es causing the relaxations and therefore monitoring them, as has been repeatedly suggested in the literature. 13,[15][16][17][18][19][20][21][22][23][24][25][26][27] NMR studies of the molecular motions taking place in glassy polycarbonates below T g show that the main characteristic motions in these systems consist of -flips of the phenylene rings around the C1C4 axis ͑see Fig. 1͒, oscillations of the ring about the same axis, and some small amplitude main-chain reorientation.…”

High-temperature steam-treatment of PBI, PEEK, and PEKK polymers with H2O and D2O: A solid-state NMR study

“…3 shows the 13 C CP/MAS NMR spectra of all PBI tensile specimens before and after exposure to D 2 O at the listed conditions. The signal assignments are in agreement with the literature [2,21,22]. Slight changes are already visible when PBI is stirred in liquid D 2 O at room temperature.…”

“…8. All signals can be assigned in accordance with the literature [4,22]. After stirring the dried PEEK (a) at room temperature in D 2 O (b), steam-treatment at 150 C (c) and at 315 C with D 2 O (d), no obvious changes are visible in the 13 C CP/MAS spectra.…”

Dielectric relaxations in poly(thiocarbonates)

“…These reorientations are produced during the motion of the phenyl groups and they are propagated not only to their own chain but to the adjacent chains and they can produce such dielectric activity as that experimentally observed. This hypothesis would be in agreement with the results obtained by Poliks et al 44 where the dipole tensors are calculated. This way only small amplitude motions would be produced in the R-C-R' group as well as in the carbonate group.…”