Cryogenic dielectric measurements corresponding to the gamma-relaxation zone have been made for poly(chloroethyl methacrylate) and poly(chloropropyl methacrylate). Molecular mechanics calculations using the Allinger MM2 force field have been carried out on monomer and trimer model compounds in an attempt to gain some insight into the possible origin of the gamma-relaxation process which occurs in these polymers at low temperatures. In both cases, we found that the molecular mechanism of oxylcarbonyl side group rotation combined with reasonable constraints on movements of the neighbouring side groups gave theoretical activation energy requirements which were in good agreement with those determined from the experiment.