Infrared studies of chain folding in polymers. v. polyhexamethylene adipamide

Systematic infrared studies of a series of polyhexamethylene adipamides (nylon 66) have resulted in the assignment of two bands to the regularly folded polymer chain. Utilizing this assignment and long-period measurements by small-angle X-ray diffraction, a method has been developed to compare the amount of regular chain folding in solution-crystallized samples precipitated at different temperatures. At high supercoolings in solution, only 60% of the chain folding which occurs has a regular structure. Annealing of the solution-crystallized samples not only produced a longer fold period but also regularized the folds. Melt-crystallized samples when annealed do not show much increase in fold period or regularization of the folds. Glass-crystallized samples show a rapid initial increase with time at a particular temperature in long period and regular folding. For the glass-crystallized samples crystallized at different temperatures for the same period of time, higher temperatures of crystallization produce longer fold periods and greater fractions of regular folds. The infrared fold bands disappear when samples consisting of regular folds are deformed but reappear after annealing.