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Adaptive polymer assemblies

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Adaptive polymers modelled on nature

One of nature's most important functions is adaptation, the ability to change in response to a changing environment. An EU-funded initiative has developed novel responsive polymer assemblies with self-healing and sensing functionalities that will have important uses in industry and biomedicine.

Climate Change and Environment

Sensing environmental changes and initiating a macroscopic response often occurs at the molecular level or, more precisely, the supramolecular level as a result of shifting supramolecular dynamic equilibria. Proteins, one of the most important natural polymers, play a critical role. Development of synthetic adaptive materials must thereby combine concepts from polymer chemistry with those of supramolecular chemistry. The ADAPTPOLY (Adaptive polymer assemblies) project enabled scientists to control the covalent interactions necessary to build polymers from individual monomers. They then built supramolecular structures of multiple tailored polymers using non-covalent interactions and self-assembly. Hierarchical structure – structure on more than one length scale – is integrally related to function. Thus, controlling the self-assembly of hierarchically structured materials enabled the creation of novel materials with tailored properties for given applications. Cyclic molecules such as porphyrins and cyclodextrins are common building blocks for supramolecular assemblies. ADAPTPOLY scientists used them to create novel supramolecular polymer materials. A number of derivatives were synthesised by researchers who investigated their self-assembly mechanisms and the potential for further modifications. Important developments include polymeric thermometers that have a memory function resulting from thermodynamic control over the supramolecular interactions. Self-healing polymers are an important type of nature-inspired adaptive material, able to repair themselves after mechanical damage. Spontaneous self-healing via formation of dynamic supramolecular structures has become an area of intense research and development. ADAPTPOLY produced polymers that form supramolecular structures via electrostatic interactions and lead to supramolecular self-healing thermoplastic elastomers. Detailed structure-morphology-property relationships were identified in this novel class of supramolecular materials. Responsive polymers were also developed that incorporate dye molecules and produce a visible (fluorescent) shift in pH responsivity in the presence of sugars. This will lead to a novel glucose sensor. Furthermore, work on block copolymers has led to a system that transitions from soluble polymer chains to aggregations (micelles) with changes in pH for controlled drug delivery. ADAPTPOLY's establishment of the Supramolecular Chemistry Research group at Ghent University will ensure that major contributions to the growing and socioeconomically important field of adaptive polymers will continue long after the project's conclusion.

Keywords

Polymers, polymer assemblies, self-healing, supramolecular, ADAPTPOLY, thermoplastic elastomers

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