A carbon-13 spin-lattice relaxation study of side chains of poly(alkyl methacrylate).

The carbon-13 spin-lattice relaxation times (T1) of the carbons in the alkyl side chains of poly (alkyl methacrylate) (butyl, octyl, dodecyl, and octadecyl), including poly (butyl methacrylate) of low molecular weights, were determined from partially-relaxed Fourier transform spectra. The T1 for polymers of high molecular weights were found to be determined by the internal motion of the side chains, and not by the overall motion of the polymer molecules. The relaxation data indicate that the internal motion of the short side chains (butyl and octyl) is restricted by interactions between the side chains, although this effect was ineffective near the free ends of long chains (dodecyl and octadecyl). These observations are interpreted in terms of the local environment around the side chains.