Characterization of Nylon-6 by N-15 Solid State Nuclear Magnetic Resonance

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Chemistry and Biochemistry


Mathematics and Natural Sciences


The solid-state 15N NMR characterization of nylon 6 is reported. Nylon 6 (20% 15N-enriched) was prepared by anionic polymerization of isotopically enriched ε‐caprolactam. The samples were prepared by three different treatments: quenched from the melt, slowly cooled and annealed, and artificially plasticized with excess caprolactam. CP/MAS spectra of the 15N-enriched samples showed a single sharp peak (α crystal form) at 84.2 ppm (relative to glycine) and a broader resonance at 87.2 ppm. Relaxation experiments were conducted to determine T1N, TIH, and T, for each sample at 300 K. The crystalline resonance was found to have T1N's of 125-416 s, consistent with crystalline nylon 6. The downfield peak had two measurable T1N's: a short component with T1N of 1-3 s and a second component with a longer T1N of 19-29 s. The two components for the noncrystalline peak are thought to belong to a liquidlike amorphous region and a more rigid "interphase" region lying between the crystalline and amorphous regions. T1ρN, measurements were consistent with two-phase (crystalline plus amorphous) morphology although the two-component decay for the amorphous region was not observed. The presence of plasticizer (caprolactam) tended to decrease T1ρN relaxation times, which is consistent with lowered Tg's. 1H T1 measurements were apparently dominated by spin diffusion that masked any differences between the regions. The chemical shift anisotropy (CSA) spectra of static samples are also shown. Motion in the amorphous region can be monitored by observing an isotropic peak at elevated temperatures. The effect of plasticizer (caprolactam) contributes to this motion. At temperatures above 100 °C, the most deshielded (σ33) component is lost from the CSA spectrum, suggesting a previously unreported anisotropic motion occurring in the rigid crystalline region. This motion is thought to be associated with the intermolecular hydrogen bond between adjacent chains.

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Journal of the American Chemical Society





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