Vibrational Spectra of Polyethylenes and Related Substances

Abstract

Fairly complete Raman spectra have been obtained of polyethylenes of different crystallinities (Marlex 50, hydrogenated Marlex 50, Marlex 20, and DYNH), Venezuela wax, n-C28H58, n-C36H74, and stearic acid. The infrared spectrum of Marlex 50 has been investigated with a Perkin-Elmer Model 112 spectrometer equipped with LiF, NaCl and CsBr prisms. On the basis of the unit cell and the space group, Vh16, determined by x-ray analysis, the 8 Raman-active unit cell fundamentals of crystalline polyethylene have been assigned as follows: Skeletal deformations 1061 (ag+b1g) and 1131 (b2g+b3g); CH2 rocking 1168 (b1g+ag); CH2 twisting 1295 (b3g+b2g); CH2 wagging 1415 (b2g+b3g); CH2 deformation 1440 (ag+b1g); sym. CH stretching 2848 (ag+b1g); asym. CH stretching 2883 cm—1 (b1g+a1g). In terms of these and 4 of the infrared-active fundamentals assigned by previous workers, it has been possible to assign all but 3 or 4 of the 60 observed infrared bands of Marlex 50. A few bands are ascribed to end groups or to amorphous polyethylene. The infrared-active CH2 wagging and twisting fundamentals (both of species au+b1u) are extremely weak and apparently masked by the corresponding bands of the amorphous phase.