Mechanochromic polymers respond to external force by changing their color. This can be achieved by the incorporation of a molecular switch such as spiropyran (SP) into polymers. SPs can be isomerized by mechanical force from their colorless form into colored merocyanines. Main chain copolymerization of spiropyrans allows investigation of their mechanochromic behavior and potential use as force sensors.
So far, several covalent polymer matrices have been used to investigate the mechanochromic response of SPs, among them poly(ε caprolactone) (PCL). Less investigated is how the mechanochromic response can be fine-tuned by substituent effects. First, PCL with differently substituted spiropyrans at the chain’s midpoint were used in order to investigate the effect of different substituents and their regiochemistry on the isomerization behavior of SPs under mechanical stress. A low activation barrier was observed for NO2 substitution of “ortho”-spiropyrans compared to no substitution (R = H).
In order to investigate phenyl-substituted “para,para” spiropyrans, a newly developed kinked polyarylene was employed as covalent matrix material. This new polyarylene (PmmpP) has a meta,meta,para connection in its backbone and exhibits excellent mechanical properties. Its high strength allows the isomerization of this molecular switch with a large activation barrier. The phenyl-substituted “para,para” spiropyran showed transient mechanochromism and was switched 25 times in force-and-release cycles. The synthesis of PmmpP was carried out by a Suzuki polycondensation in three steps from commercial starting materials.
To further capitalize on the simplicity and properties of PmmpP, a two step synthesis of a semifluorinated kinked polyarylene was demonstrated by direct arylation polycondensation with tetrafluorobenzene (F4). This partially fluorinated PmmpF4 was synthesized with a variety of side-chains. Resulting polymers exhibited a large range of glass transition temperatures, allowing for the production of tailor-made smart materials.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:74725 |
| Date | 18 May 2021 |
| Creators | Kempe, Fabian |
| Contributors | Sommer, Michael, Spange, Stefan, Technische Universität Chemnitz |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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