- The major goal of this study was to elucidate the conformation of the "crystalline" component of poly(dichlorophosphazene) chain, and consequently make vibrational band assignments based on the known chain conformation.
Experimental Fourier transform infrared (FT-IR) and Raman spectra of ( NPCl(,2) )(,n) in the amorphous and semi-crystalline states were obtained. Polarized infrared spectra were obtained in order to facilitate symmetry analysis. Additionally, the infrared digital subtraction technique was employed to accentuate and assign the bands associated with the contributions of "crystalline" and "amorphous" components. Symmetry analysis of ( NPCl(,2) )(,n) was undertaken by considering the inherent symmetry of the various conformational models where the infrared and Raman activity in addition to dichroism considerations could be predicted from selection rules and compared to experimental results.
The combination of results from the steps above, nonetheless, revealed no clear picture in addressing any specific preferred conformation for the crystalline microstructure of ( NPCl(,2) )(,n). Subsequently, it appeared that theoretical normal coordinate (NCA) calculations might greatly assist in attainment of the goal of this study. The NCA calculations, however, necessitated the derivation of a consistent valance force field (VFF) from relevant model compounds hexachlorocyclotriphosphazene, (NPCl(,2))(,3), and octachlorocyclotetraphosphazene, (NPCl(,2))(,4). A preliminary VFF was developed by consecutive refinements of unknown force constants based on the observed vibrational frequencies of (NPCl(,2))(,3). This VFF could not satisfactorily be transferred to the NCA of (NPCl(,2))(,4) or ( NPCl(,2) )(,n); possibly due to the unique geometry of a six-membered ring. On the other hand, a very simple common VFF was derived employing the experimentally observed frequencies of the two crystalline modifications of (NPCl(,2))(,4) by consecutive co-refinements, which could be transferred to the NCA of ( NPCl(,2) )(,n).
The combination of experimental and NCA results based on the molecular line symmetry C(,2), nonetheless, allowed the order and form of the normal modes to be observed with reasonable confidence.
- Dissertation Note:
- Ph.D. The Pennsylvania State University 1981.
- Source: Dissertation Abstracts International, Volume: 43-03, Section: B, page: 7440.
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