We present results from solid-state one-dimensional magic-angle spinning exchange nuclear magnetic resonance (NMR) experiments aimed to investigate the influence of the side-chain length on the main- and side-chain dynamics in selected members of the poly-n-acrylates series, poly(n-hexyl methacrylate) and poly(n-butyl methacrylate). The molecular dynamics of the different molecular sub-units in the slow-motion region was investigated by recently developed exchange NMR methods at temperatures close to the glass transition temperatureTg. The molecular mobility of main-chain, side-chain and carboxyl carbons could be assigned to different relaxation processes as identified by dielectric and mechanical relaxation and caloric methods. Information about both the time constants as well as the geometry of the processes could be obtained. The main aim of this paper is to discuss differences in the molecular origins of the different processes in dependence on the length of the side chains. Conclusions about the coupling of main- and side-chain motions in dependence of the side-chain length are drawn. These details are not detectable by caloric and relaxation methods but could easily be realized from exchange NMR data.