The infrared multiple absorption bands in the 1300-1100 cm(-1) range, attributed to the v(a)(C-C-O) vibration of PMMA, and the carbonyl shift of the solid-state NMR spectra, have been analyzed in terms of conformational restrictions. The Av(2)/Av(1) infrared ratio, calculated from the absorbances of vl (at 1260-1275 cm(-1)) and vs (at 1240 cm(-1)), is found to give the ratio of the backbone conformational energy relative to the overall energy of the chain segment. From this ratio, it is suggested that there are cooperative motions between the backbone and the side chain in i-PMMA, but not in s-PMMA.