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The effect of temperature on the infrared absorption frequencies of polyethylene and ethylene–propylene copolymer films
Author(s) -
Brockmeier Norman F.
Publication year - 1968
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1968.070120916
Subject(s) - materials science , ethylene , copolymer , absorption band , polyethylene , infrared , atmospheric temperature range , dispersion (optics) , analytical chemistry (journal) , polymer , molecular physics , chemistry , optics , composite material , thermodynamics , organic chemistry , physics , catalysis
The frequency shifts of the six prominent infrared absorption bands were measured for films of polyethylene and ethylene–propylene copolymer as a function of temperature. Three bands (at 720, 731, and 1473 cm −1 ) shifted to higher frequency, and three bands (at 1463, 2849, and 2918 cm −1 ) shifted unexpectedly to lower frequency as the sample temperature was decreased. The greatest shift occurred with the CH 2 rocking band, which increased from 730.2 to 734.2 cm −1 as the temperature was decreased from 313 to 22°K. The shift usually ceased in the temperature range from 40 to 110°K, probably because some kind of molecular motion ceased. Four mechanisms are discussed in an attempt to account for the different frequency shifts: bulk contraction with decreasing temperature, an increase in dispersion forces between chains, variation in the length and coupling of the vibrating chain molecule, and a change in the planar zigzag conformation of the chain molecule. Thermal contraction is sufficient to explain most of the observed frequency shifts. The CH 2 stretching modes (2849 and 2918 cm −1 ) may be shifted to lower frequency by an increase in the dispersion forces between chains, caused by contraction. The displacement of the 1463 cm −1 band‐shift curve is an indication of the sample density. The displacements of the 1473 and 731 cm −1 band‐shift curves are indications of the proportion of propylene in the ethylene copolymer.