| Abstract: | The magnetic circular dichroism (MCD) spectra of syndiotactic and isotactic polymers which contain aromatic chromophores have been found to be sensitive to configurational and conformational differences. For isotactic polymers it was determined that as the aromatic ring moved farther from the main chain the ration of B terms of the polymers to those of their model compounds reached a minimum but increased significantly when the aromatic ring was separated from the main chain by four atoms. This enhancement of MCD is believed to be caused by the alignment of the more flexible side chains which would allow the interaction of the aromatic rings with neighboring groups and could result in a favorable mixing of the ester electronic transition with the aromatic 1A1g?1B2u transition. This effect was not felt to any great extent by the syndiotactic polymers because the necessary nearest-neighbor interaction was sterically unfavorable. The ratio of the B terms of isotactic poly(phenyl methacrylate) to its model compound decreased as the polymer coil expanded, whereas it increased for the syndiotactic polymer. This effect reflects the different changes that the side chain interaction and orientations undergo in these polymers during coil expansion. The MCD ratios for iso- and syndiotactic poly(phenylethyl methacrylate) were not so sensitive during coil expansion. The ratio of the dipole strengths of the polymers and model compounds paralleled the MCD results, but the ultraviolet (UV) technique was less sensitive than MCD to subtle conformational differences. Poly(benzyl methacrylate) and benzyl pivalate were unsuitable systems for studying the MCD effect because the B terms of these materials approached zero. |
