Preparation and some properties of nylon 46

Nylon 46 was synthesized from the salt of 1,4-diaminobutane and adipic acid. High molecular weight polymers could be obtained by reaction for 1 hr at 215°C in a closed system and at least for 1 hr in vacuo at a temperature in the range 290-305°C. The reactions at 290°C were found to have taken place in the solid state and those at 305°C in the melt. The highest molecular weights (Mw ca. 45,000) were obtained by reaction at 290°C with a nylon salt with a pH of 7.8-8.0. The molecular weight characteristics were studied with end-group analysis, viscometry, light scattering, and ultracentrifugation. The polymers were found to be gel-free and monodisperse (Mw/Mn ~ 1.15). Films could be cast from formic acid. From x-ray diffraction patterns, measured on such films, spacings of 3.74 and 4.30 Å were calculated, whereas a long period of 66 Å was also found. The infrared spectra showed all the usual amide bands of even-even polyamides. The melting temperature was found to vary between 283 and 319°C, depending on the thermal history of the sample. Water absorption measured on a cast film showed this to be very hygroscopic (7.5% at 65% RH), while a highly crystalline sample absorbed only little water (1.6% at 65% RH)