Poly anisotropy

With h 6) - 1/sin 0)5(0 — Oq), one obtains the same result as given by (4.58), which implies that the anisotropy of the/factor cannot be derived from the intensity ratio of the two hyperfine components in the case of a single crystal. It can, however, be evaluated from the absolute/value of each hyperfine component. However, for a poly-crystalline absorber (0(0) = 1), (4.66) leads to an asymmetry in the quadrupole split Mossbauer spectrum. The ratio of l-Jh, as a function of the difference of the mean square amplitudes of the atomic vibration parallel and perpendicular to the y-ray propagation, is given in Fig. 4.19. 

D Biren, BG Kabra, SH Gehrke. Effect of initial sample anisotropy on the solvent sorption kinetics of glassy poly(2-hydroxyethyl methacrylate). Polymer 33 554-561, 1992. 

Figure 34 (a) UV and CD spectra and (b) FL spectrum and FL anisotropy of poly(n-decyl-(S)-2-methylbutylsilylene), 88, in isooctane at 20 °C.204 Reproduced with permission from Fujiki, M. Macromol. Rapid Commun. 2001, 22, 539-563, 2001 Wiley-VCH. 

The magnitude of the chemical shift anisotropy depends on the bonding situation and the nucleus gyromagnetic ratio. Since the bonds formed by lithium in organolithium compounds or other lithiated systems are mainly ionic, the anisotropy of the lithium chemical shift is generally small. It is more pronounced for Li than for Li. Li spectra are dominated by the quadrupolar effect and the CSA contribution to the Li lineshape is often negligible. Exceptions are compounds with poly-hapto bound lithium, such as... 

The angle dependence of the spin soliton in randomly oriented ladder poly-diactylene has also been investigated79 by pulsed HFEPR at 94 GHz. The shape of the 0-anisotropy-resolved nutation spectrum was discussed on the basis of the EPR transition moments and the differences between spin relaxation times. Reliable assignments of hyperfine couplings to the p-protons (P-H) of the alkyl side chains were achieved with the support of W-band ENDOR measurements. No significant orientational dependence of the 7i and Ti processes was found in terms of the isotropy of the p-H-hyperfine interaction. 

The anisotropy of piezoelectricity in oriented polymer films is quite different among polymers. The piezoelectric effect in oriented polypeptide films is greatest when elongated along a direction at 45° to the draw-axis. On the contrary, the effect is most remarkable for elongation along the draw-axis for roll-drawn poly(vinylidene fluoride) film. 

Figure 9 shows the result by Fukada, Date, and Hirai (1966) for uniaxially drawn poly(y-methyl L-glutamate) film (PMLG). The conformation of the chains is predominantly the a-helix. The sample was drawn twice as the original length and the frequency of stress was 20 Hz. The observed anisotropy is well expressed by the tensor (59) which leads to the d-constant of the film for elongational stress in the film plane (yz-plane),... 

The anisotropy of polarizability can be positive (eg, polycarbonate) as well as negative (eg, polystyrene). This offers the possibility of minimizing birefringence by copolymerization or blending of suitable polymers with the right mixture ratio, eg, blends of poly(phenylene ether) (PPE) and polystyrene (PS). The magnitude of birefringence of axial-symmetrically oriented polymers vs their molecule orientation has been described (182). 

---