Two-dimensional Infrared Spectroscopy Study of Polypropylene C—H Bending Vibration

The effect of temperature on the chemical structure of polypropylene was studied using two-dimensional infrared spectroscopy. In the frequency range of 1500~1350 cm-1, the molecular structure of polypropylene was studied by one-dimensional infrared spectroscopy, second derivative infrared spectroscopy and fourth derivative infrared spectroscopy of C-H bending vibration(δC-H). Two-dimensional infrared spectroscopy was then used to study the effect of temperature on the δC-Hinfrared absorbance intensity of polypropylene. The polypropylene δC-Hmainly included methyl asymmetrical bending vibration mode(δas CH3), methyl symmetrical bending vibration mode(δs CH3) and methylene bending vibration mode(δCH2). With increase of the measurement temperature, the sequence of intensity changes in the δC-Hinfrared absorbance intensity of polypropylene was δCH2-2(1464 cm-1)>δCH2-1(1475 cm-1)>δas CH3(1455 cm-1)>δs CH3(1375 cm-1). The study demonstrated the key roles of two-dimensional infrared spectroscopy in the analysis of thermal denaturation of the polymer packaging materials.