Abstract
Recent interest in emerging processes for polymer manufacturing and bio-based chemistries for direct chemical recycling/upcycling has motivated new research focused on a deeper understanding of atomic-scale polymer properties and how they influence macroscopic phenomena. Uncovering the fundamental properties of polymers that give rise to macroscopic behavior could enable new pathways for improved recyclability or utilization of alternative "greener" polymer analogues. In this study, the neutron vibrational spectrum was measured for a film of biaxially oriented polyethylene terephthalate (BoPET) using inelastic neutron scattering (INS), to investigate the relationship between the structure and dynamics of a widely used polymer. Compared to conventional spectroscopic techniques, the use of INS is advantageous for polymeric materials due to the absence of selection rules (i.e., all transitions are allowed), broad-band energy range, and considerable sensitivity to hydrogen modes. In order to distinguish the vibrational modes caused by trans and gauche rotational isomerism, the normal modes of vibration were calculated from a density functional theory-optimized structure of crystalline PET (cPET), representative of the all-trans state, and compared with INS from "highly crystalline" PET powder. Although in- and out-of-plane wagging of hydrogens on the ring structure exhibit significant contribution to both BoPET and cPET spectra, the wagging, rocking, and twisting modes of hydrogen on the ethylene glycol group are, in most cases, conformation-specific. These results were further rationalized by investigating the role of hyperconjugation in stabilizing both conformations using the natural bond order method. Through comparison of experimental and calculated INS results, this work provides the fundamental basis for discovering the role of structure and dynamics in shaping the macroscopic properties of PET and polymer analogues.
| Original language | English |
|---|---|
| Pages (from-to) | 7491-7501 |
| Number of pages | 11 |
| Journal | Journal of Physical Chemistry A |
| Volume | 126 |
| Issue number | 41 |
| DOIs | |
| State | Published - Oct 20 2022 |
Funding
The authors would like to thank Prof. J.Z. Larese, who passed away suddenly November 2021, for significant contributions in advancing both instrumentation and applications of INS, in particular for materials such as PET. J.Z.L. was the primary driving force behind the design and construction of VISION at the Spallation Neutron Source, which enabled the data and results in this manuscript. This work was supported by the Eastman Innovations Network (EIN) of Eastman Chemical Company. Z.D.S. would like to acknowledge Dr. Konstantinos Vogiatzis at the University of Tennessee, Knoxville, for meaningful discussions. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract no. DE-AC02-976SF00515. WAXS measurements of BoPET samples were conducted at beamline 11-3. The authors acknowledge the support from Bart Johnson, beamline engineer at SSRL beamline 11-3.
