Eight amorphous polyethers and poly(ether ketones) were synthesized and characterized by gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical thermal analysis. Polymers containing bulky, cyclic 2,2’-biphenyl side groups were found to have the highest glass transition temperatures, were more thermally stable and exhibited the highest intramolecular barriers to rotation. Incorporation of perfluorophenylene groups resulted in internal plasticisation and a relative lowering of T-g. The steepness of cooperativity plots determined from Williams-Landel-Ferry shift factors correlated with the rigid nature of the polymer chains, but not with the broadness of the relaxation (characterized by the Kohlrausch-Williams-Watts stretch exponent beta) as predicted by the coupling model. A beta-process observed in the polymers containing cyclic biphenyl side groups was similar in appearance to a typical "structural" relaxation. The position, intensity, and breadth of the gamma-process was sensitive to chemical structure and absorbed moisture.