Infrared Spectra of High Polymers . II . Polyethylene *

The infrared spectrum of polyethylene has been obtained between about 3000 cm-1 and 70 em-I, polarization measurements on oriented specimens having been obtained to about 350 em-l. Assignments of the fundamentals are made with the help of a group theory analysis. The assignment of the controversial CH. wagging mode is discussed in detail and especially in terms of new evidence from the spectra of n-paraffins, both as single crystals and as polycrystalline aggregates. It is shown that this mode is to be assigned to a weak band at 1369 cm-l. A satisfactory determination of the bands which arise from CHa groups is also made possible by a study of the paraffin spectra. The splitting of bands in the spectrum is conclusively shown to arise from interactions between molecules in the crystalline phase. The nature of this interaction is discussed in terms of recent theories.