A new non-acidic mixed solvent system for nylon nuclear magnetic resonance: cis amide quantitation in nylons and model amides

Use of binary fluorinated alcohol-chloroalkane solvents is demonstrated for solution nuclear magnetic resonance (n.m.r.) analysis of nylons. These solvents, through a combination of low viscosity and low acidity, promote decreased linewidths and allow observation of features masked by traditional acidic solvents. Peaks for cis amide linkages have been identified for selected nylons and model compounds by 1H, 13C and 15N observation. Surprisingly, the cis content increases with increase in the number of methylene linkages between amide groups for both A-B and AA-BB nylons. The temperature dependencies of the cis amide contents of nylon 6,6 and a model amide were followed by 1H and 13C n.m.r. over the useful temperature range of the binary solvent (−10 to 75°C); both showed an increase in cis content up to the onset of desolvation and/or line-broadening caused by amide hydrogen exchange.