Infrared Study of the Nonequilibrium Glassy State of Polymers (Frequency Shifts)
Joss, Brian Louis
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https://hdl.handle.net/2142/71838
Description
Title
Infrared Study of the Nonequilibrium Glassy State of Polymers (Frequency Shifts)
Author(s)
Joss, Brian Louis
Issue Date
1986
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Polymer
Abstract
The nonequilibrium glassy state of polymers has been examined using Fourier-Transform Infrared (FTIR) spectroscopy. The nonequilibrium nature of polymer glasses induces a physical aging process which results in time dependent changes in physical, mechanical and thermodynamic properties. Valence coordinate deformation (VCD) is proposed as an intramolecular stress associated with the vitrification and aging process. VCD involves the displacement of bond lengths R, bond angles (theta), internal rotation angles (phi) and nonbonded interaction distances q from their equilibrium positions and has been shown both experimentally and theoretically to be a source of infrared frequency shifting effects in mechanically stressed polymers. Frequency shifting effects are expected to appear in quenched amorphous polymers until physical aging produces a more nearly equilibrium state. Experimentally, changes in frequency were measured as a function of temperature in quenched and annealed samples of PMMA, PS and PC. For the carbon backbone polymers (PMMA, PS), only C-C stretching vibrations of the backbone were found to be sensitive to sub-T(,g) annealing. Side-chain and nonskeletal vibrations were found to display identical behavior in quenched and annealed samples. These results are consistent with a VCD mechanism of frequency shifting. For PC, backbone vibrations behaved identically in quenched and annealed samples. This behavior is contrary to what was found for the skeletal vibrations in carbon backbone polymers and is thought to be associated with the main chain flexibility and low intramolecular barriers to rotation in PC. In general, the measurement of changes in vibrational frequency as a function of temperature was established as a useful technique to identify thermal transitions, mechanical relaxations, molecular mobility and the extent of aging in polymer glasses.
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