528 TROXELL, SCHERAGA
Macromolecules
Electric Dichroism and Polymer Conformation. 11. Theory of Electric Dichroism, and Measurements on Poly (n-butyl isocyanate) Terry C. Troxell and Harold A. Scheraga * Department of Chemistry, Cornel1 UniGersity, Ithaca, New York 14850. Receioed April 22, 1971
ABSTRACT: The theory of electric dichroism (ED), with the permanent dipoles of helical macromolecules being oriented by a static external electric field, is discussed. The effects on the ED of orientation due to an anisotropic polarizability, flexibility of the backbone and side chain, aggregation, and polydispersity in the degree of polymerization (DP) are also considered. This theory, and a new method for measuring ED, are applied here in a study of poly(r2-butyl isocyanate) in nonpolar solvents over a range of DP from 200 to 2400. The ED results show that the polymer behaves as a rigid rod up to DP 600, with an onset of flexibility at higher DP. The ED spectrum down to 192 mp shows only positive dichroism which arises from a weakly dichroic band at
