Structural characterization of nylon 7 by solid-state nuclear magnetic resonance, differential scanning calorimetry and attenuated total reflectance Fourier transform infra-red spectroscopy

Abstract Samples of commercial nylon 7 were given different thermal or precipitation histories. Structure and crystallinity were followed by d.s.c., solid-state n.m.r. and attenuated total reflectance Fourier transform infra-red spectroscopy (ATR FT i.r.). Heat of fusion and melting temperature values ranged from 52 to 93 J g −1 and 228 to 242°C, respectively. Surprisingly, annealing did not give material with the greatest heat of fusion although it possessed the highest melting point. Solid-state 13 C and 15 N n.m.r. methods were used to observe the amorphous and crystalline fractions. For example, the amide nitrogens show resonances near 86.5 ppm in amorphous domains, near 84 ppm in α-crystals and near 89 ppm in γ-crystals. 15 N cross-polarization/magic angle spinning spectra of solution cast samples contained peaks consistent with all three domains in various intensity ratios but with the γ-peak being the most intense for most samples. Solid-state 13 C spectra contained peaks which supported the presence of these phases but with the α-phase peaks predominating. Treatment of solution-cast thin films with aqueous KI I 2 gave materials whose n.m.r. spectra contained peaks consistent with these three phases in different ratios than for the initial solution-cast samples. Spectra of the melt crystallized samples contained peaks for amorphous and α-domains only. 13 C spin-lattice relaxation ( T 1 ) magnetization decays could be fit to two or three exponentials ( T 1 s of hundreds of milliseconds, a few seconds and hundreds of seconds) consistent with semicrystalline polymer behaviour. T 1 values for the long-relaxing component ranged from 350 to 23 s for the annealed and precipitated samples, respectively. Amide V bands near 682 cm −1 , assigned previously to the α-phase, were present in the ATR FT i.r. spectra of all the samples. However, the chemically treated and solution cast samples contained additional bands at 690 and 620 cm −1 due to the γ-phase. Spectra of quenched samples contained bands not seen in the other spectra.