Abstract
Proton magnetic resonance spectra of nine substituted polystyrenes: polymers of o‐methyl, m‐methyl, p‐methyl, p‐chloro‐, 2,4‐dimethyl‐, α,β,β′‐trideutero‐, β‐ deutero‐, 2,6‐dimethyl‐4‐tert‐butyl‐, and p‐tert‐butylstyrene, in addition to five polystyrene samples differing in molecular weight (M̄~n~'s from 1.25 × 10^5^ to ∼35 × 10^5^) or tacticity have been obtained at temperatures from 77 to above 400°Kg. Measurements have also been made on p‐tert‐butyltoluene, 2,4‐dimethylstyrene, and 2,6‐dimethyl‐4‐tert‐butylstyrene. All polymers studied were found to exhibit single‐component derivative line shapes and to undergo rapid motional narrowing with increasing temperature in the region of the glass transition; in this region the line width for atactic polystyrene was found to be essentially independent of molecular weight. At lower temperatures a gradual line narrowing effect was also observed for some of the polymers, even near 77°K., and is attributed to limited phenyl or substituted phenyl group oscillation. This effect was apparent for polystyrene, poly‐α,β,β′‐trideutero‐, poly‐β‐deutero‐ poly‐p‐chloro, and poly‐p‐methylstyrene, less apparent for the o‐ and m‐methyl compounds and the p‐tert‐butyl‐substituted polymer, and absent for the 2,4‐dimethyl and the 2,6‐dimethyl‐4‐tert‐butyl polymers. By a comparison of experimental second moments with approximate ones obtained from theory, it is concluded that rotation of all methyl groups attached directly to benzene ring for all polymers studied is taking place at 77°K. For both p‐tert‐butylsubstituted polymers and the low molecular weight analogs, a motional narrowing process occurs in the ≤77° to 150°K. region, and for all but 2,6‐dimethyl‐4‐tert‐butylstyrene this is attributed to rotation of the methyl groups in the tert‐butyl part of the molecule; for the latter compound, onset of rotation of one of the methyl groups attached directly to the ring in addition to the methyl in the tert‐butyl part is responsible for the line narrowing. The contributions of various proton interactions to the total second moment of polystyrene and its derivatives are discussed.