2019 Fiscal Year Research-status Report
Improving Self-Healing of Supramolecular Polymer Networks Using Halogen-Bonding and Living Cationic Polymerization
| Project/Area Number |
19K15635
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| Research Institution | Kyoto University |
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Principal Investigator |
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| Project Period (FY) |
2019-04-01 – 2021-03-31
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| Keywords | halogen bonding / monomer synthesis / cationic polymerization / self-assembly |
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| Outline of Annual Research Achievements |
Herein we report the progress in the first year of this project to investigate the influence on formation of supramolecular polymer networks (SPN) using more flexible polymers (by using vinyl ethers that can be polymerized via cationic polymerization) and more selective intermolecular interactions (by using halogen bonding). The synthesis of three novel vinyl ether monomers for cationic polymerization that are capable of halogen bonding was achieved. Synthesis conditions were optimized and the polymerization of these monomers was investigated. Monomers with similar chemical structures but no halogen bonding moieties were also synthesized and polymerized to determine the extent of halogen bonding. Initial polymerization was uncontrolled and the use of a proton trap (DTBP) was found to be necessary. Various conditions for polymerization were investigated thoroughly and controlled polymerization was achieved. Study of more complex polymer structures was also started. While earlier than planned, initial studies on the halogen bonding abilities of the monomers and homopolymers was also carried out using small molecule donors and measuring the peak shift in 19FNMR spectroscopy. Polymers were found to have more significant halogen bonding ability than small molecules.
Year two of the project will focus on the synthesis of a variety of polymer structures by introducing non-halogen bonding monomers into these copolymers. The self-assembly structures will be investigated to determine what the ideal conditions for forming SPN based on these materials are.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The synthesis of the proposed halogen bonding monomers for cationic polymerization was achieved and conditions for synthesis were optimized. Polymerization conditions were then carefully investigated. While suitable polymerization conditions were found for these monomers, a more significant investigation of the optimal polymerization conditions than originally envisioned was carried out. This is partially due the fact that initial polymerization conditions produced an uncontrolled polymer. Through the use of a proton trap additive (DTBP), however, controlled polymerization was achieved. The choice of Lewis acid was also found to have significant influence on the stability of the polymer products and the formation of unwanted byproducts. After careful investigation, good conditions were determined, enriching the study of these novel monomers. Due to the more in-depth investigation of the polymerization conditions, the synthesis of various polymer structures did not proceed as quickly as originally planned and only homopolymers were thoroughly investigated.
Alternatively, some parts of the project proceeded faster than anticipated. Once monomers and homopolymers were synthesized, their halogen bonding ability was investigated earlier than planned. Shifts in 19FNMR spectra reveal halogen bonding interactions and show clear differences between the three different halogen bonding monomers. Additionally, the homopolymers tested show better halogen bonding ability than the monomers, which is encouraging for the investigation of these materials in supramolecular polymer networks.
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| Strategy for Future Research Activity |
The next step in this research is to synthesize and investigate an even wider variety of polymer structures incorporating the new halogen bonding monomers. Specifically, we will aim to synthesize ABA triblock copolymers, AB block copolymers and random copolymers. As conditions for synthesizing novel polymer structures are established and a variety of ratios and polymer lengths are considered, the formation of supramolecular structures, particularly those based on halogen bonding, will be investigated.
Furthermore, while halogen bonding was demonstrated with small molecule acceptors, we plan to expand the scope of the type of acceptors used. To achieve facile synthesis of acceptors we plan on using a RAFT-living cationic polymerization method to investigate the formation of unique ABA triblock copolymers. While the target cationogen, has been reported recently in the literature, our study will focus on developing conditions which will allow for the formation of ABA triblock copolymers that incorporate acceptor moieties.
Overall, the goal is to determine what structures promote the formation of supramolecular polymer networks, and if possible to consider the properties of these materials as compared to similar systems based on radical polymerization methods and compare hydrogen bonding systems to halogen bonding systems. It is anticipated that the in-depth study of the network materials will extend beyond the funding period for this research.
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| Causes of Carryover |
For this project, the optimization of the polymer synthesis conditions and the investigation of the halogen bonding abilities using 19FNMR and other methods was far more extensive than originally anticipated. While considering the research plans for the year, an additional 100,000 was applied for in December to ensure that this research could continue without concerns of inability to purchase necessary chemicals to synthesize monomers. And indeed, these funds ensured that the needed supplies to continue monomer synthesis were obtained. The purchase of supplies to synthesize more halogen bonding monomers from December to the end of March, did not exceed the amount applied for, however and 82,135 was left. Since it was anticipated that monomer synthesis would still proceed at a significant rate for the next phase of this project, namely the synthesis of a wide variety of polymer structures, it was determined that these funds could be used effectively in the second fiscal year.
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