Raman spectroscopic study of CO2 sorption process in poly methyl methacrylate

Raman spectra of poly methyl methacrylate (PMMA) in contact with compressed CO₂ were measured, to investigate effects of CO₂ sorption on structure of the PMMA chain. The solubility and diffusivity of CO₂ in PMMA were estimated from temporal variations of intensities of CO₂ peaks. The PMMA structure was analyzed from temporal variations of vibrational energies of PMMA peaks. The results show that the vibration energies of C H stretching modes of PMMA increase with CO₂ sorption, whereas those for skeletal vibration modes decrease. These energy shifts are attributed to elongational deformation of PMMA. The PMMA structure is deformed with stretching of the chains as a bundle. From energy shifts of the CO₂ peaks, the size of the CO₂ accommodated space between the bundles is estimated to be 1.6–1.9 nm. Furthermore, it was observed that the vibrational energies of the PMMA modes in foamed glassy PMMA differ from the values in glassy PMMA without foams. This result suggests that the local structure of the PMMA chain changes with the process of the CO₂ sorption and/or foaming. The local structure of the PMMA chain might be one of the dominant factors governing the properties of cellular materials. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 831–842, 2008