Magnetic circular dichroism studies of polystyrene solutions

Abstract

AbstractThe magnetic circular dichroism (MCD) spectra of “atactic” and isotactic polystyrene solutions have been found to be sensitive to configurational and conformational differences. The ratio of B terms for “atactic” polystyrene (predominantly syndiotactic) to that of cumene was found to pass through a minimum as the coil expanded in various solvents. The ratio of dipole strengths D also passed through a minimum. For isotactic polystyrene and cumene the ratio of B terms increased with increasing coil size in the range of solvents utilized. The ratio of B terms of isotactic polystyrene over atactic polystyrene was found to go through a maximum as the coil expanded whereas the ratio of dipole strengths was found to continuously decrease. These results have been interpreted on the basis of the change in short range and long range orientation and interaction distances between chromophores during coil expansion. It is concluded that the microscopic conformation of isotactic and atactic polystyrene are very different in very good solvents. The B/D ratio for cumene was found generally to decrease with increasing solvent power.