Modern Polymer Spect..

Figure 3-22. Sample eigenvectors in
the in-plane bending region for a
single chain of mixed 25% DCI in
HCI. The distribution of defects is
the same as that given in Figure
3-21.
dl
Wz360.6 cm-'
unquestionably: Z = 1, 2719.5 cm-' (strong); Z = 2, 2708.5 cm-' (weak or inactive)
and 2729.5 cm-' (inactive); Z = 5-6, 2700.5 cm-' (strong) and Z = 8-9,
2739.5 cm-' (inactive).
An example of resonance modes which cannot provide any signal characteristic
of a given defect is given in Figure 3-23 for the same chain as that considered in
Figure 3-21 and 3-22. In this case the bending modes are considered where (see
above) frequency branches overlap. Because of intramolecular coupling, collective
vibrational waves extending along large domains of the chain are generated and do
not provide any useful and characteristic signal which may contribute with a weak
and broad background.
It is realized that the situation found for impure simple 3D lattices is found
also for the single chain considered here and very likely may be found for other
polymers containing an increasing concentration of defect. In the HCl (or DC1)
stretching region these mixed crystals behave as 'two-mode system' or 'persistencetype'
system. 'Amalgamation-type' behavior is observed in the bending range where
sections of density of states overlap both for HCl and DCl [98].