A Remarkably Large Phase‐Transition Effect in a Random Copolymer of Oligo(ethylene glycol) Methyl Ether Methacrylate (OEGMA)₅₀₀ Induced by the Photochemistry of the 2‐(Hydroxyimino)aldehyde Group

Abstract

The effect of UV irradiation on the cloud points (CP) of aqueous solutions of a random 1:1 copolymer of oligo(ethylene glycol) methyl ether methacrylate (OEGMA500) and a 2‐(hydroxyimino)aldehyde (HIA) functionalized methacrylate is presented. CPs are determined by visible spectroscopy and dynamic light scattering (DLS). 1H and 13C NMR experiments are carried out in D2O and DMSO‐d6 on the polymer and on an HIA‐functionalized model of the photoresponsive repeat unit. UV‐irradiated solutions exhibit an unprecedented increase of the phase‐separation temperature for an OEGMA photoresponsive copolymer (10–22 °C, depending on concentration and irradiation conditions). Phase separation is reversible with little hysteresis. With both pristine and irradiated polymer solutions, aggregate dimensions are <10 nm (DLS) at room temperature. Aggregates of >100 nm form at the CP and gradually grow as temperature increases, whereas the light‐induced processes of the repeat unit model in DMSO‐d6 are well identified (e.g., oxime E/Z isomerization and Norrish‐Yang cyclization of the aldehyde moiety), it is not straightforward to extrapolate such behavior to the polymeric solution in water. The remarkably large phototriggered thermal effect in the present work motivates further investigations on the solvent‐dependent photochemistry of HIA as a promising functional group for the synthesis of multi‐stimuli responsive materials.

Playing construction with the monomer toy box for the synthesis of multi‐stimuli responsive copolymers by reversible deactivation radical polymerization protocols

“…Smith et al 162 achieved higher order morphologies and electric field‐responsive (electrophoretic) nano‐objects by including a cationic monomer in the shell copolymer. Hydrophilic random copolymers exhibiting light‐sensitive cloud points 2,163 may be used as block constituents in more complex architectures. On the other hand, when a light‐sensitive moiety is located in the hydrophobic micellar core, the nanoaggregate can be photo‐stimulated to disassemble or modify its LCST.…”

“…As an alternative to the creative assembling of readily available monomers to obtain copolymers endowed with multiple responsivity or to introducing specific functionalities by post‐polymerization reactions, many research groups resort to the synthesis of monomers containing functional groups with specific tasks and then copolymerize them with readily available ones. In some cases, the novel monomer is responsive to more than one stimulus 2,214–221 . This approach entails advantages and difficulties.…”

“…As a result, an amplification of the triggered response and, sometimes, an interdependence of one response with another can be observed. Such is the case, for instance, of dual light‐ and temperature‐responsive polymers that change their transition temperatures as a consequence of irradiation 2–4 . This is fundamentally different from the working principle of molecular machines, which respond by individual motions to external stimuli.…”

Click‐Connected 2‐(Hydroxyimino)aldehydes for the Design of UV‐Responsive Functional Molecules

“…Therefore, the photoreactions of oxime and carbonyl compounds have been attracting a renewed attention in contemporary applications, such as the manipulation of soft materials properties [12] and synthetic photochemistry and photocatalysis [13] . For instance, we recently showed that the photochemistry of the HIA group has a remarkably large impact on the physico‐chemical behavior of aqueous solutions of copolymers of OEGMA and an HIA‐functionalized methacrylate [14] . Applications of the HIA to CBO photoisomerization can be envisaged in metal ligation and sensors [15,16] .…”

Unusually Chemoselective Photocyclization of 2-(Hydroxyimino)aldehydes to Cyclobutanol Oximes: Synthetic, Stereochemical, and Mechanistic Aspects

“…Within the framework of our continuing investigation of the 2-(hydroxyimino)­aldehyde (HIA) functionality, as a versatile structure in multistimuli-sensitive polymers, we have been studying the physico- and photochemical properties of several HIAs. − …”