RATES OF CONFORMATIONAL TRANSITIONS IN SOLUTIONS OF RANDOMLY COILED POLYMERS .2. NUCLEAR MAGNETIC RESONANCE STUDY OF HINDERED ROTATION AROUND AMIDE BONDS IN SIDE CHAINS

Poly(N,N-dimethylacrylamide) and an acrylic acid copolymer containing 10 mol% N,N-dimethylacrylamide were studied by nmr spectroscopy in D2O solution. The N(CH3)2 portion of the spectrum, in both the homopolymer and the copolymer, consists of a doublet which coalesces at 96 ± 2° and a singlet which shows no evidence of separating down to 13.5°. The data are best interpreted by assuming that for some of the dimethylamide groups in the atactic polymer the chemical shift difference of NCH3 groups cis and trans to the carbonyl oxygen is too small to be resolved under our experimental conditions. Poly(N-acetylaziridine) was studied in aqueous phenol solution containing 92.5 wt % phenol. The nmr spectrum at ambient temperature contained a doublet for the CH3CO group with a coalescence temperature of 79 ± 2°. This doublet may be interpreted as resulting from differences in the relative conformations of neighboring amide groups in the polymer chain. © 1969, American Chemical Society. All rights reserved.