Modern Polymer Spect..

3.18 Band Broadening and Confonnational Flexibility 173
Figure 3-42. Hexadeuteropropane:
10-
n
0 " d+(CHZ)
I I I
Figure 3-43. Ranian spectrum in the C-Hstretching
range of C~lH44: (a) solid and ib) melt.
a
3050 3000 2950 2900 2850 2800 cm-I
1. For short chains, the antysimmetric d- mode broadens in the Raman spectrum
by increasing temperature and sometimes shifts upward in frequency (Figure
3-42), while d+ neither shifts substantially nor broadens. (See also Figure 3-37.)
2. For long polymethylene chains and polyethylene at melting, the strong d-
modes collapses into a featureless very broad scattering and by increasing temperature
shifts its maximum towards higher frequencies (Figure 3-43).
3. For crystalline n-alkanes the width of d- does not increase with teniperature up
to a few degrees below melting (Figure 3-44).
4. When n-alkanes are inserted as clathrates in urea channels, the width of d- is