SEGMENTAL DYNAMICS IN THE CRYSTALLINE PHASE OF NYLON-66 - SOLID-STATE H-2 NMR

Solid-state deuterium NMR spectroscopy coupled with line-shape simulations has been used to examine the segmental dynamics in selectively deuterated nylon 66 polymers over a wide temperature range. Contributions to the experimental line shape from crystalline and noncrystalline domains may be quantitatively decomposed by employing spin-lattice relaxation time discrimination above -50 °C. N-D and C-D groups in the crystalline domains are found to undergo spatially heterogeneous librational motion (not discrete jumps) both below and above the Brill transition. The N-D groups undergo rapid, but quite restricted, librational motion at all temperatures below the melting point, reflecting the preservation of the hydrogen bonds. The amplitude of motion of the methylene groups in each moiety is very similar, but those located in the adipoyl moiety execute a larger amplitude motion than those located in the hexamethylene diamine moiety at temperatures below the Brill transition. Above the Brill transition, the amplitude of the rapid librational motion of all of the methylene group C-D bonds is quite similar. The mean correlation time of the librational motion is substantially longer for the N-D groups (~300 ps) than for the C-D groups (~40 ps). The motion of the C-D bonds is the same for both dry and wet (2 wt %) polymers. Furthermore, a complete redetermination of the temperature dependence of the X-ray crystal structural parameters has been carried out to facilitate a critical comparison of the experimental structure and the structural requirements of various models of molecular motion. © 1990, American Chemical Society. All rights reserved.