Abstract
Different mechanisms of thermochromism have been identified in thermoresponsive, azobenzene-containing copolymers that are augmented by the lower critical solution behaviour.
Highlights
A large number of materials show a change of colour with temperature, which is generally termed thermochromism
The target compound could be synthesised in reasonable yields around 68% when utilising the coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) with 4-dimethylaminopyridine as a catalyst
A synthesis route to novel azo dye monomers by esterification of methyl red to N-(2-hydroxyethyl)acrylamide (MREAm) via carbonyldiimidazole coupling could be established for all three positional isomers of the dye
Summary
Polymers entails a manifold of systems with either the polymer itself being thermochromic or the polymer being a matrix for thermochromic dyes, complexes or particles.[7]. In MR, the azonium form is stabilised via a quinoidal resonance structure and intramolecular hydrogen bonding, rendering it the preferred structure.[24] Adsorption on silica gel results in a colour change of MR from red (acidic) to orange (neutral/basic) upon heating The authors attribute this effect to an increase of basic sites at the silica gel surface at low temperatures due to release of water and an increase in acidity of the dye at higher temperatures.[25] Another halochromic azobenzene has been shown to have the opposite behaviour when immobilised in ion-exchange micelles: the protonated form was more stable than the deprotonated form. For the monomeric and polymeric systems, the thermochromic behaviour was investigated in alcoholic and aqueous media under neutral, slightly acidic, and strongly acidic conditions
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