Crystallization of polyamides under elevated pressure. 7. Effect of reequilibration on the annealing of nylon 6 under elevated pressure

The effect of reequilibration reactions on the annealing of nylon 6 under elevated pressure has been investigated. The rate of the reactions was controlled by masking of end groups and varying the water content of the polyamide. In presence of 6% water, the initial rate of improvement of the crystals at 0.65 GPa and 284°C increases greatly, as concluded from the sharp rise in the melting temperature, the heat of fusion, and the long period. This is related to a drastic acceleration of the hydrolysis of amide groups, indicated by an almost instantaneous 10-fold decrease in the molecular weight, as revealed by viscometry. Annealing of extremely dry specimens under similar experimental conditions results in the generation of free radicals, and network formation slows down the perfection process. The present results strongly support the previous suggestion that chain scission is a predominant step in the annealing of polyamides under elevated pressure.