Vibrational Spectra of Polyethylenes and Related Substances

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.