Mechanophores in self-healing polymers: Influence of mechanical bond activation on the self-healing performance of polymers

• Applicant: Dr. Martin Hager
• Subject Area: Preparatory and Physical Chemistry of Polymers ; Polymer Materials
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398304946

• Final Report Year: 2023

Final Report Abstract

Within the project, different potential mechanophores for the integration into intrinsic self-healing polymers were investigated. These self-healing polymers are based on reversible covalent and supramolecular polymers. Three main classes of possible mechanophores were investigated for integration into reversible polymer networks. The basic principle of these mechanophores were donor-acceptor systems, which are to be integrated into the reversible bonds. First, imines based on donor-acceptor building blocks were investigated. Coloured oligomers could be synthesized here. However, these oligomers or the underlying building blocks could not be integrated into the desired polymer networks (e.g., polymethacrylates), as their stability was insufficient or no polymerisable groups could be introduced. Furthermore, Diels-Alder and Alder-ene systems based on triazolinediones were investigated. Here it was shown that the stability of the free unbound triazolinedione is not sufficient and that the occurring side reactions would limit the optical evaluation of the reversibility too much. The most promising systems were based on reversible Michael addition between an acceptor and thiols. Although the basic systems could not be modified with other chromophoric units, the reversible Michael addition could be followed very well using Raman spectroscopy. Polymers based on this reversible crosslinking also show shape memory behaviour in addition to self-healing. By correlating Raman spectroscopy with mechanical investigations, both exchange and dissociation reactions could be detected. In addition to the design of the binding units, the detailed characterisation of self-healing polymers could also be advanced within the framework of the project. In this context, different approaches could be investigated that make crack healing quantifiable. Furthermore, the healing kinetics could also be monitored.

Publications

• A novel approach for the quantification of scratch healing of polymers. Polymer Testing, 90, 106699.
  Abend, Marcus; Tianis, Lukas; Kunz, Clemens; Zechel, Stefan; Gräf, Stephan; Müller, Frank A.; Schubert, Ulrich S. & Hager, Martin D.
  
• Quantification of the scratch-healing efficiency for novel zwitterionic polymers. NPG Asia Materials, 12(1).
  Dahlke, Jan; Kimmig, Julian; Abend, Marcus; Zechel, Stefan; Vitz, Jürgen; Schubert, Ulrich S. & Hager, Martin D.
  
• In-depth characterization of self-healing polymers based on π–π nteractions. Beilstein Journal of Organic Chemistry, 17, 2496-2504.
  Meurer, Josefine; Hniopek, Julian; Ahner, Johannes; Schmitt, Michael; Popp, Jürgen; Zechel, Stefan; Peneva, Kalina & Hager, Martin D.
  
• The time-dependency of the healing behavior of laser-scratched polymer films. Polymer Testing, 100, 107264.
  Abend, Marcus; Zechel, Stefan; Tianis, Lukas; Kunz, Clemens; Enke, Marcel; Dahlke, Jan; Gräf, Stephan; Müller, Frank A.; Schubert, Ulrich S. & Hager, Martin D.
  
• Thiol‐ene Reaction as Reversible Covalent Bond for the Design of Shape‐Memory Polymers. Macromolecular Materials and Engineering, 308(8).
  Shohraty, Farhad; Hniopek, Julian; Meurer, Josefine; Zechel, Stefan; Schmitt, Michael; Popp, Jürgen & Hager, Martin D.