Natural abundance solid-state nuclear magnetic resonance spectroscopy (NMR) of nitrogen-15 (N-15) was applied to investigate the films of nylon-6 and their blends with poly(propylene oxide) (PPO). The NMR N-15 results allowed us to identify the crystalline forms present in these blends and also confirmed the previous NMR results obtained by C-13-NMR study. From all NMR data the antiplasticization phenomena and plasticization effects caused by PPO content, in the blends were characterized. The polyoxide action is a function of its proportion. However, because the samples were prepared by solution casting, the residual solvent action cannot be ignored. The N-15 chemical shift changes were influenced by both PPO and residual solvent. (C) 2003 Wiley Periodicals, Inc.