Thermal gelation of the nylon 6,6-calcium chloride-methanol system

An attempt was made to clarify phase transition behavior of nylon 6,6 in a solvent mixture of calcium chloride and methanol on cooling. The nylon 6,6 solution showed turbidity and generated a thermally reversible gel during slow cooling and rapid quenching, followed by aging. Gelation temperature remarkably depended on cooling rate, as well as molecular weight and polymer concentration. The Differential Scanning Calorimetry (DSC) thermogram of the system, that was cooled down at low cooling rate from the dissolution temperature to 25 degrees C and followed by aging for various periods, exhibited two endothermic peaks, both of which monotonically grew with increase of aging time up to 100 h. The results of the temperature dependence of X-ray diffraction of the gel aged for 2 days at 25 degrees C revealed that crystals generated and grew during gelation. The melting of the crystal was responsible for the endothermic peak at higher temperature side in the DSC thermogram on heating. C-13 NMR data on the gel suggested that the solvent molecules, especially calcium chloride associated by methanol molecules, formed an organometal coordination complex with the nylon 6,6 and acted as crosslinking agents in the gel. The gel formed by rapid quenching was regarded as amorphous, because the DSC thermograph showed no apparent endothermic peak on heating. The base line shifted to the endothermic side as usually observed for glass transition of thermoplastic polymers and the gel showed only a hallow pattern in the X-ray diffraction diagram.