The crystalline structure of polyamide-12 (PA12) was studied by solid-state 13C nuclear magnetic resonance (NMR) as well as by synchrotron wide- and small-angle X-ray scattering (WAXS and SAXS). Isotropic and oriented PA12 showed different NMR spectra ascribed to γ- and γ′-crystalline modifications, respectively. On the basis of the position of the first diffraction peak, the isotropic γ-form and the oriented γ′-form were shown to be with hexagonal crystalline lattice at room temperature. When heated, the two PA12 polymorphs demonstrated different behaviors. Above 140 °C, the isotropic γ-PA12 partially transformed into α-modification. No such transition was observed with the oriented γ′-PA12 phase even after annealing at temperatures close to melting. A γ′–γ transition was observed here only after isotropization by melting point. Various structural parameters were extracted from the WAXS and SAXS patterns and analyzed as a function of temperature and orientation: the degree of crystallinity, the d-spacings, the Bragg's long spacings, the average thicknesses of the crystalline (lc) and amorphous (la) phases, and the linear crystallinity xcl within the lamellar stacks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3720–3733, 2005
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