The conformational dynamics both in the solution state and in the bulk in the structurally modified polycarbonate of Bisphenol-A (BPAPC) with a cyclohexyl moiety in place of the isopropylidine group has been examined using n.m.r. The solution C-13 spectra allow the identification of the intramolecular dynamics at the repeat unit level and the consequences of the existence of microstructure. The cyclohexyl ring dynamics suggest that the ground state conformation is considerably strained relative to a pure chair form. This leads to a lower barrier for the ring inversion in agreement with modeling conclusions. In the solid state this phenylene mobility is further restricted and at low temperatures the bridgehead carbon C5 shows doublet character. As the temperature is raised, motion increases along with the free volume and this follows the onset of motion of the phenylene rings. The differential dynamics of the two phenylenes results in a broadening of the mechanical relaxation which correlates with their dynamics. The position and breadth of the shear mechanical relaxation corresponding to the dynamics monitored by the collapse of the C5 carbon can be obtained from the n.m.r. data. The conclusion indicated is that the more restricted (axial) phenylene ring is the one whose motion correlates with the high temperature side of the mechanical loss and it is the phenylene ring dynamics which correlates with the unusual shift in the low temperature loss characteristic of the cyclohexyl substitution and the increased breadth of the relaxation relative to BPAPC.