Solid-State NMR Investigation of Nylon 12

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Polymers and High Performance Materials


Nylon 12 (polylauramide) was synthesized with > 99% N-15 labeling at the amide nitrogen using N-15-labeled potassium phthalimide in the Gabriel method. CP/MAS NMR was used to evaluate the crystal forms present in the samples which were either quenched from the melt in liquid nitrogen, annealed, or precipitated from a mixture of phenol and absolute ethanol (84:16 by weight). Commercially available nylon 12 was treated similarly to the synthesized polymer. Differences were observed in both the N-15 and the C-13 CP/MAS NMR spectra between the annealed, quenched, and precipitated samples consistent with the presence of gamma, gamma', and alpha + gamma crystal forms. The N-15 spin-lattice relaxation times (T1N) for the labeled samples were shown to increase in the following order consistent with decreasing mobility: gamma' < gamma less-than-or-equal-to alpha. The respective T(g)'s and T(m)'s for the gamma (ca. 50 and 184-degrees-C), gamma' (ca. 45 and 177-degrees-C), and alpha (ca. 40 and 169-degrees-C) forms (measured by DSC) were consistent with literature values. Precipitated samples showed two melting endotherms for two crystal forms whose presence was confirmed by two peaks in the solid-state N-15 NMR spectrum at chemical shifts consistent with alpha and gamma crystal forms. Comparison with two amide model compounds was also made with respect to C-13 chemical shifts for carbons alpha to the carbonyl (C-alpha) and the nitrogen (C(N)).

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