Infrared studies of polymer chain folding I. Linear polyethylene

An infrared method has been developed for studying folding in linear polyethylene utilizing the assignment of the 1350 cm −1 and 1304 cm −1 bands to gauche methylene units. Gauche methylenes can occur in the disordered regions or as a part of the fold; their absorption coefficients are different in the two regions and allow one to determine their contribution to each region by simultaneous solution of the absorbance equations. The results indicate the fold structure of slow‐cooled bulk polyethylene is essentially the same as the folds of solution crystallized polyethylene and no disordered regions containing gauche methylenes exist. Rapidly cooled samples contain gauche methylenes in anomalous structures which tend to disappear during annealing. Annealing at 120°C. produces no change in the fold structure of single crystals.