Infrared Spectra of Polyethylene Crystals

Abstract

The infrared absorptionspectrum of polyethylene crystals grown from solution was investigated. Intensities of bands, attributed to defects, in the region 1250–1400 cm−1 were observed to change with heat treatment, first decreasing and then increasing as the temperature of the treatment was increased in the range 120°–135°C. This observation is interpreted in terms of reduction of the number of folds accompanied by introduction of a different type of defect. The doublet at 720–731 cm−1 was monitored during the process of refolding at T≈130°C. A vestige of the high‐frequency component was observed at all times, indicating the persistence of space‐group symmetry. The suggestion of morphological similarity of polyethylene crystallized from solution and from the melt is supported by the similarity of their spectra. Two new weak bands at 692 and 1243 cm−1 were observed in the spectra of specimens cooled with liquid nitrogen. The frequency 1243 cm−1 is nearly equal to that predicted for a CH2 twisting mode which is inactive under selection rules for an isolated molecule.