The H-1 NMR technique is used to study the motion of monomer units on the interface poly(ethylene oxide) chains grafted on silica. The NMR line narrowing effect by high speed rotation of the specimen is observed in samples of different molecular weight. Our experiments allow us to determine two correlation times: tau(c), characteristic of the fast motion and tau(1), characteristic of the slow motion corresponding, respectively, to intra- and inter-monomer units. tau(c) and tau(1) are determined for all the samples of different molecular weight. This procedure is also applied at different temperatures for the same molecular weight. Results are coherent with linewidth and relaxation times measurements.