NORMAL-MODE ANALYSIS OF INFRARED AND RAMAN-SPECTRA OF CRYSTALLINE ISOTACTIC POLY(METHYL METHACRYLATE)

Infrared spectra of oriented and Raman spectra of nonoriented samples of crystalline isotactic poly(methyl methacrylate) (i-PMMA) have been measured. These vibrational spectra have been analyzed by means of normal-mode calculations, using a combined valence force field transferred without refinement from hydrocarbons and from methyl acetate. Calculations have been done for single chain 5/1 and 10/1 helical backbone conformations. Best agreement in the low-frequency region is found between the observed and calculated frequencies for the 10/1 structure. Infrared and Raman bands over the entire spectral region can be satisfactorily interpreted on the basis of the potential energy distributions and dispersion curves for the 10/1 helical conformation of the single i-PMMA chain in the double-stranded structure. © 1990, American Chemical Society. All rights reserved.