ISSN:
0025-116X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Light scattering, neutron scattering and viscosity measurements on a nematic and a smectic polymethacrylate demonstrate the presence of molecularly disperse coils in solution. For the nematic polymer, toluene is a theta solvent, the behaviour familiar from conventional polymers (unperturbed coil conformation) being exhibited at the theta point. The isotropic melts likewise contain unperturbed coils; in the case of the nematic polymers, however, the coils in the melt have a radius of gyration which is about 30% smaller than that in solution at the theta point. In the liquid-crystalline phase, the mean radii of gyration in both cases are identical to the corresponding parameters in the isotropic melt. In the nematic material, however, the coils can be shown to have a substantial anisotropy, the radius of gyration parallel to the director being about 20% smaller than that at right angles to this direction. On the basis of a theoretical chain simulation, a model for the main-chain conformation has been developed which takes into account both short-range interactions along the main chains and three-dimensional interactions by the oriented side groups. This model indicates the degree of orientation from which a change in the mean radius of gyration can be expected. Wide-angle neutron scattering experiments on smectic polymer provide information about the main-chain distribution in the smectic phase. The main chains are present in a substantially higher concentration between the smectic layers, but there are hints that they do not have a true two-dimensional arrangement.
Zusätzliches Material:
9 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/macp.1988.021890616
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