Counterintuitive Photomodulation of the Thermal Phase Transition of Poly(methoxy diethylene glycol acrylate) in Aqueous Solution by trans-cis Isomerization of Copolymerized Azobenzenes

Structure-property relationship in functionalized azobenzene photoswitches and their supramolecular behavior

Herein, we report the design, synthesis, and supramolecular behavior of 30 structurally diverse photoresponsive azobenzene molecular systems. To establish structure-property relationships, azobenzenes appended with N-picolinyl and/or N-benzyl groups tethered directly through carboxamides or via triazolylmethyl carboxamide linkages were explored. We have evaluated the photoswitching characteristics and thermal stability of the Z isomers through systematic studies. All the targets were also screened for their aggregation behavior and supramolecular aspects. Among all the derivatives, a few carboxamide-based systems formed microcrystals upon aggregation, showing light responsiveness. In contrast, the derivatives tethered via triazolylmethyl carboxamide linkage exhibited hydrogel formation with excellent water-absorbing capacity. All supramolecular aspects of the morphology of the microcrystal and hydrogel states and their stimuli-responsiveness have been studied using spectroscopy and various microscopic techniques.

Boosting the photo-switchability of double-responsive water-soluble polymers by incorporating arylazopyrazole dyes

Dual thermo- and light-responsive water-soluble copolymers that respond to exclusively non-invasive triggers are obtained by functionalising poly(N,N-dimethylacrylamide) with arylazopyrazole side chains. The light-induced E-Z (trans-Z) photo isomerisation of these dyes provides an exceptionally effective photo-switch, which can reversibly shift the LCST-type phase transition temperatures by almost 25 K.

Enhanced Stain Removal and Comfort Control Achieved by Cross-Linking Light and Thermo Dual-Responsive Copolymer onto Cotton Fabrics

Enhanced capabilities of stain removal and comfort control are simultaneously achieved by the light and thermo dual-responsive copolymer poly(triethylene glycol methyl ether methacrylate- co-ethylene glycol methacrylate- co-acrylamide azobenzene) (P(MEO₃MA- co-EGMA- co-AAAB)) cross-linked on cotton fabrics. P(MEO₃MA- co-EGMA- co-AAAB) is synthesized by sequential atom transfer radical polymerization with a molar ratio of 8 (MEO₃MA):1 (EGMA):1 (AAAB). The MEO₃MA units induce a thermoresponsive behavior to the copolymer. The hydrophilicity of the copolymer films can be further improved by the light-induced trans- cis isomerization of the AAAB units with UV radiation. The copolymer is facilely immobilized onto cotton fabrics with 1,2,3,4-butane tetracarboxylic acid as cross-linker. Due to the immobilization of P(MEO₃MA- co-EGMA- co-AAAB), the hydrophilicity of the fabric surface is increased under UV radiation. Therefore, by simply installing a UV light source in the washing machine, better capability of stain removal is realized for the cross-linked cotton fabrics. It can prominently reduce the consumption of energy, water, and surfactants in laundry. In addition, the trans-AAAB units of the copolymer cause the cross-linked P(MEO₃MA- co-EGMA- co-AAAB) layer to be more hydrophobic under ambient conditions. Hence, the copolymer can more easily collapse and form a porous structure on the fabrics. Thus, the air permeability of cotton fabrics cross-linked with P(MEO₃MA- co-EGMA- co-AAAB) is enhanced by 13% at human body temperature as compared to P(MEO₃MA- co-EGMA), giving improved comfort control during daily wear.

Effect of chain architecture on the swelling and thermal response of star-shaped thermo-responsive (poly(methoxy diethylene glycol acrylate)-block-polystyrene)3 block copolymer films

The effect of chain architecture on the swelling and thermal response of thin films obtained from an amphiphilic three-arm star-shaped thermo-responsive block copolymer poly(methoxy diethylene glycol acrylate)-block-polystyrene ((PMDEGA-b-PS)₃) is investigated by in situ neutron reflectivity (NR) measurements. The PMDEGA and PS blocks are micro-phase separated with randomly distributed PS nanodomains. The (PMDEGA-b-PS)₃ films show a transition temperature (TT) at 33 °C in white light interferometry. The swelling capability of the (PMDEGA-b-PS)₃ films in a D₂O vapor atmosphere is better than that of films from linear PS-b-PMDEGA-b-PS triblock copolymers, which can be attributed to the hydrophilic end groups and limited size of the PS blocks in (PMDEGA-b-PS)₃. However, the swelling kinetics of the as-prepared (PMDEGA-b-PS)₃ films and the response of the swollen film to a temperature change above the TT are significantly slower than that in the PS-b-PMDEGA-b-PS films, which may be related to the conformation restriction by the star-shape. Unlike in the PS-b-PMDEGA-b-PS films, the amount of residual D₂O in the collapsed (PMDEGA-b-PS)₃ films depends on the final temperature. It decreases from (9.7 ± 0.3)% to (7.0 ± 0.3)% or (6.0 ± 0.3)% when the final temperatures are set to 35 °C, 45 °C and 50 °C, respectively. This temperature-dependent reduction of embedded D₂O originates from the hindrance of chain conformation from the star-shaped chain architecture.