Structural Characterization of Nylon-7 by Solid State Nuclear Magnetic Resonance, Differential Scanning Calorimetry and Attenuated Total Reflectance Fourier Transform Infrared-Spectroscopy

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Polymers and High Performance Materials


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 FTi.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 13C and 15N 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. 15N 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 13C 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 KII2 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. 13C spin-lattice relaxation (T1) magnetization decays could be fit to two or three exponentials (T1s of hundreds of milliseconds, a few seconds and hundreds of seconds) consistent with semicrystalline polymer behaviour. T1 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 FTi.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.

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