dielectric absorption studies of a variety of polar solutes containing rotatable groups and of some analogous rigid molecules dispersed in atactic polystyrene have been carried out. preparation of the solutions as solid disks, and the dielectric measurements using a general radio 1615-a capacitance bridge and a hewlett-packard q-meter with appropriate temperature-controllable cells have been described. the experimental data as a function of frequency at different temperatures were subjected to analysis by a series of computer programmes written in the api language. the activation energy barriers opposing the dielectric relaxation processes were obtained by the application of the eyring rate equation. different types of polar rigid molecules have been studied mainly to provide sources of relaxation data and activation parameters for comparisons with those of flexible molecules of analogous size. attempts have also been made to correlate the activation parameters with size, shape, and rotating volume of the rigid molecules. studies of some nitrogen-containing heterocyclic rigid molecules and the comparison of their eyring analysis results with those of the analogous non-heterocycles showed no significant molecular interaction with the polymer matrix. of the flexible molecules, a wide variety of compounds containing the carbonyl group have been studied. intramolecular processes involving the rotation of the polar carbonyl group with one or more segments from the alkyl substituents have been observed for phenyl alkyl (aryl-alkyl) and dialkyl ketones. significantly higher energy barriers to acetyl group rotation around the c — n bond have been found in n-acetylimidazole in which the n atom is involved in ring conjugation. however, this barrier appeared to have been reduced considerably due to the effect of saturation as in n-acetyl-4-piperidone...