Self-healing coatings by reversible crosslinking: Mechanistic investigations of defined model systems on the molecular level using linear and non-linear Raman microspectroscopy
Final Report Abstract
The joint project was devoted to the synthesis of novel polymeric materials, which contained reversible crosslinks based on (hetero)Diels-Alder units. These reversible groups, which could be triggered by temperature, should be utilized for the self-healing of polymer coatings based on these materials. It was possible to design a new “all-in-one” polymer systems, which contained all binding units required for a subsequent crosslinking of the polymer. In contrast to many reported examples, no low molar mass crosslinker is required in order to obtain crosslinked polymer films. Moreover, the ratio of the reversible crosslinkers could be adjusted within the systems. The thermal properties of the resulting polymer network could be tuned by the corresponding comonomer. Polymer coatings, based on these materials, revealed a fast scratch healing (up to 100% within 30 to 60 minutes) at elevated temperatures (> 120 °C). The required healing temperature of the polymers could not be lowered by the introduction of more polar comonomers. However, the utilization of polar comonomers, which feature still a rather low glass transition temperature, still allows the fabrication of polar self-healing polymer coatings. The hetero-Diels-Alder reaction offers in principle lower healing temperatures. However, the investigated systems (except the already established dithioesters), e.g., thioketones, cyanothioacrylamides, suffer from synthetic drawbacks (lower yields, stability, compatibility to the polymerization) that these systems are not suitable for the fabrication of self-healing polymer coatings. Vibrational spectroscopy (i.e. IR spectroscopy and Raman spectroscopy) was successfully applied to the synthesized self-healing materials. Both methods allow to follow the cleavage (and reformation) of the reversible binding unit, i.e. give information about the microscopic processes, which can be combined with the macroscopic information (e.g., mechanical properties, scratch healing). In summary, polymers based on the reversible Diels Alder reaction are interesting candidates to obtain self-healing materials. These materials feature one intrinsic drawback, the required higher healing temperatures. Depending on the utilized binding units, this temperature can be lowered in comparison to stand system (furan and maleimide). However, interestingly hetero Diels Alder systems described in the literature still require higher temperatures. Consequently, these materials are interesting for applications, in which higher temperatures can be tolerated and preferably, in which higher temperatures are generated during the usage of these materials.
Publications
- One-component intrinsic self-healing coatings based on reversible crosslinking by Diels Alder cycloadditions. Macromol. Chem. Phys. 2013, 214, 1636-1649
J. Kötteritzsch, S. Stumpf, S. Hoeppener, J. Vitz, M. D. Hager, U. S. Schubert
(See online at https://doi.org/10.1002/macp.201200712) - Self-healing materials via reversible crosslinking of poly(ethylene oxide)-block-poly(furfuryl glycidyl ether) (PEO-b-PFGE) block copolymer films. Adv. Funct. Mater. 2013, 23, 4921-4932
M. J. Barthel, T. Rudolph, A. Teichler, R. M. Paulus, J. Vitz, S. Hoeppener, M. D. Hager, F. H. Schacher, U. S. Schubert
(See online at https://doi.org/10.1002/adfm.201300469) - Triggered and self-healing systems using nanostructured materials. Nanotechnology Rev. 2013, 2, 699-723
J. Kötteritzsch, U. S. Schubert, M. D. Hager
(See online at https://doi.org/10.1515/ntrev-2013-0016) - A rheological and spectroscopic study on the kinetics of self-healing in a single-component Diels–Alder copolymer and its underlying chemical reaction. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1669-1675
R. K. Bose, J. Kötteritzsch, S. J. Garcia, M. D. Hager, U. S. Schubert, S. van der Zwaag
(See online at https://doi.org/10.1002/pola.27164) - Insights into the mechanism of polymer coating self-healing using Raman spectroscopy Appl. Spectr. 2014, 68, 541-548
S. Vasiliu, B. Kampe, F. Theil, B. Dietzek, D. Döhler, P. Michael, W. H. Binder, J. Popp
(See online at https://doi.org/10.1366/13-07332) - Monitoring the chemistry of self-healing by vibrational spectroscopy – current state and perspectives. Mater. Today 2014, 17, 57-69
L. Zedler, M. D. Hager, U. S. Schubert, M. J. Harrington, M. Schmitt, J. Popp, B. Dietzek
(See online at https://doi.org/10.1016/j.mattod.2014.01.020)
