ISSN:
0449-2978
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
It is argued on the basis of a simple model for a polymer chain that characteristics of conformation can be determined from the analysis of the frequency distribution of backbone vibrations. In a chain with one degree of freedom per repeat unit, a fold tends to uncouple the motions on each side of the fold. This transfers highest and lowest modes towards the mean value. Conversely, a local unfolding of a random chain enhances the coupling and produces out-of-band modes. From the ordering of these modes, statistical aftereffects can be detected. The Green's function method allows a calculation of the single localized mode as a function of angular parameters. The dynamical matrix elements of the Kirkwood-Pitzer model are calculated for a folded polyethylene backbone chain. The eigenvalue distribution is determined with the Givens-Sturm procedure. It indicates a one-to-one correspondence between modes in the vicinity of 670 cm.-1 in the stretch-bend gap and chain folds, for low concentration of folds. We conclude that conformations should have two characteristic parameters distinctively reflected in the frequency distribution, namely the range of allowed dihedral angles and the ordering of configurations along the chain. The frequency distribution for a given conformation depends however on the force constant ratios when the degree of freedom is greater than one. Interpretation of the frequency spectrum is then made by adjustment of dynamical and geometrical parameters. These are seen to be dependent variables with respect to the spectrum.
Additional Material:
19 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1968.160060310
