NMR observations of drawn polymers. IX. Chain mobilization and water mobility in nylon 66

Abstract

AbstractWide‐line NMR spectra of nylon 66 fibers have been obtained at different alignment angles between the fiber axis and the magnetic field, at varying water contents (H2O and D2O), and at different temperatures. At 28°C the spectrum of the dry fibers consists of a nearly structureless broad line. At water regains of 1.4% by weight (dry basis) and higher a sharp line appears which originates from highly mobile water molecules. The width of this line decreases with increasing water content, implying an increase of water mobility. Moreover, the width is a function of the alignment angle; this shows that the water is not reorienting isotropically owing to specific water‐polymer interaction. The amount of mobile water is always smaller than the amount of water absorbed. At water contents close to saturation, a mobile polymer line appears with a width intermediate between the broad line (immobile polymer) and the sharp water line. This line, most clearly observed at an alignment angle of 0°, is due to a shift of the αa process to lower temperatures in the presence of water. A similar line is observed in the dry fibers at 120°C. It is shown that the αa process decreases the NMR second moment only slightly. The shift of the high temperature drop in second moment to lower temperatures in the presence of water is therefore interpreted as due to a shift of the αc process, and not of the αa process, to lower temperatures.