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Ethylene vinyl alcohol (EVOH) is an oxygen barrier polymer used to prevent premature degradation of food, pharmaceuticals, and other products due to its semicrystallinity, strong intermolecular interactions, and consequently low free volume. EVOH is made using traditional free-radical copolymerization, which leads to little structural regularity. We utilized ring-opening metathesis polymerization (ROMP) to determine how regioregularity impacts the barrier properties of EVOH-related materials. A regioregular (head-to-tail) polymer was synthesized from ROMP of 3-acetoxycyclooctene, followed by hydrogenation and deacylation to give a linear, highly regioregular EVOH (PH3OHCOE) containing the equivalent of 75 mol % ethylene units. The same process was carried out with 5-acetoxycyclooctene, but the resulting polymer (PH5OHCOE) is regiorandom. Both polymers were compared to an industry benchmark, EVOH-44, containing 44 mol % ethylene units. After processing, differential scanning calorimetry showed that the semicrystalline PH3OHCOE had a higher melting temperature and enthalpy of melting compared to semicrystalline PH5OHCOE, indicating that PH3OHCOE is more crystalline. This was confirmed by wide-angle X-ray scattering (WAXS). WAXS, rheological studies, and polarized optical microscopy showed that PH3OHCOE has a more well-defined crystal structure, a higher degree of hydrogen-bonding between −OH groups, and a higher glass transition temperature compared to PH5OHCOE. These differences were also highlighted in their tensile behavior, where PH3OHCOE and EVOH-44 exhibited brittle failure compared to the ductile behavior observed for PH5OHCOE. Oxygen barrier testing demonstrated that regioregular PH3OHCOE had an oxygen permeability more than a factor of 3 lower than regiorandom PH5OHCOE but still higher than EVOH-44, while water barrier testing showed that PH3OHCOE had the lowest water permeability, more than 6 times lower than EVOH-44. These results highlight the importance of regioregularity on the barrier properties of EVOH-like materials and show that structural regularity can lower oxygen permeability while maintaining low water permeability at the low vinyl alcohol content.
Bibliographical noteFunding Information:
The authors thank The Dow Chemical Company for partial financial support of this research. The authors thank Dr. Jeff Munro, Dr. Colin Li Pi Shan, Dr. Thomas Peterson, and Dr. Christopher Thurber for input. All rheology was carried out in the College of Science and Engineering Polymer Characterization Facility, University of Minnesota, which has received capital equipment funding from the NSF through MRSEC. WAXS was carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through MRSEC. The authors would like to thank Dr. Geoffrey Rojas (UMN Charfac) and Dr. Victor Young (UMN X-ray Crystallographic Laboratory) for conducting room-temperature WAXS experiments and Donald Massey for performing barrier measurements in the Center for Flexible Packaging, Clemson University. The authors would also like to thank Yoon-Jung Jang, Dr. Stephanie Liffland, and Dr. Caitlin Sample for helpful discussion.
© 2023 American Chemical Society.
- functional polyolefins
- gas barrier
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- 1 Active
9/1/20 → 8/31/26
Project: Research project