Measurements of dielectric relaxation and viscoelastic relaxation at audio- and radio-frequencies have been made on dilute solutions of polymethyl acrylate, polymethyl methacrylate, methyl methacrylate citraconic anhydride copolymers, poly n-butyl methacrylate and poly nonyl methacrylate (3,3,5-trimethyl hexyl). For polymers of molecular weight about 5 × 105 the viscoelastic relaxation occurs at a reduced frequency below about 102 to 103 Hz, and is slightly dependent on polymer structure. However, the dielectric relaxation occurs at much higher frequencies, and is dependent on the structure of groups attached to the polymer backbone, but not on the nature of the ester group. For methyl acrylate, methyl methacrylate and the copolymer the relative dielectric relaxation frequencies closely parallel the rates of diffusion-controlled chemical reactions. This is not so with the various alkyl methacrylates. From these results it is suggested that the dielectric relaxation is not associated with a low order normal mode of motion of the molecules, but is a cooperative backbone and side group motion (αβ process) which does not require complete rotation of the backbone C—C bonds. The rearrangement necessary for chemical reaction, on the other hand, does seem to require major backbone reorientation.