The microscopic rotational dynamics of a main chain liquid crystalline (LC) poly(ether) in its nematic phase is studied in detail by nonlinear least squares analysis of ESR spectra in the slow motional regime. This complements results reported in an accompanying paper, which focuses on macroscopic translational diffusion using the DID-ESR (dynamic imaging of diffusion by ESR) technique. Far infrared 250 GHz ESR spectroscopy is used to determine the magnetic g and A tensors of the 3-carboxy-PROXYL spin label attached to the LC polymer. ESR spectra of the labeled polymers of varying molecular weights are analyzed to yield the rotational diffusion coefficients and orientational order parameters. Different cases of the degree of macroscopic alignment are observed in these samples and accounted for in the simulations. For molecular weights lower than 11 000 (for both tracers and matrices), the rotational diffusion coefficient R is found to correlate with the molecular weight of the polymer matrix and to be independent of the molecular weight of tracer, suggesting the importance of free volume for end-chain motion. Macroscopically aligned samples, corresponding to lower molecular weight LC polymers, show an inverse correlation of R with order parameter, consistent with observations previously reported for nonpolymeric LCs, which were associated with free volume effects.