In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(alpha-n-alkyl) acrylates in which it is possible to change the length of the alkyl chain. We have evaluated the Narayanaswamy parameter, x, which controls the relative contribution of temperature and of structure to the relaxation time, the apparent activation energy, Delta h*, and the nonexponentiality parameter, beta, of the stretched exponential response function. The results suggest that x increases while Delta h* decreases and beta remains constant as the length of the side chain increases. This allows us to comment on the effect of chemical modification on the relaxation kinetics.