Abstract
Coumarin-containing vinyl homopolymers, such as poly(7-methacryloyloxycoumarin) (P1a) and poly(7-(2′-methacryloyloxyethoxy)coumarin) (P1b), show a lower critical solution temperature (LCST) in chloroform, which can be controlled by the [2 + 2] photochemical cycloaddition of the coumarin moiety, and they are recognized as monofunctional dual-stimuli-responsive polymers. A single functional group of monofunctional dual-stimuli-responsive polymers responds to dual stimuli and can be introduced more uniformly and densely than those of dual-functional dual-stimuli-responsive polymers. In this study, considering a wide range of applications, organogels consisting of P1a and P1b, i.e., P1a-gel and P1b-gel, respectively, were synthesized, and their thermo- and photoresponsive behaviors in chloroform were investigated in detail. P1a-gel and P1b-gel in a swollen state (transparent) exhibited phase separation (turbid) through a temperature jump and reached a shrunken state (transparent), i.e., an equilibrium state, over time. Moreover, the equilibrium degree of swelling decreased non-linearly with increasing temperature. Furthermore, different thermoresponsive sites were photopatterned on the organogel through the photodimerization of the coumarin unit. The organogels consisting of homopolymers of coumarin-containing methacrylate exhibited unique thermo- and photoresponsivities and behaved as monofunctional dual-stimuli-responsive organogels.
Highlights
Multi-stimuli-responsive gels have attracted particular attention because of their potential for application in highly functionalized materials [1,2,3]
The copolymer hydrogels of NIPAM and acrylic acid can be transformed into PNIPAM-based hydrogels containing pendant crown ether groups by the side-chain reaction of acrylic acid units, and the resulting hydrogels have been applied to lead-sensing materials whose volumes change depending on the Pb2+ concentration [5]
We have reported that coumarin-derivative homopolymers, such as poly(7-methacrylo ryloyloxycoumarin) (P1a) and poly(7-(2’-methacryloyloxyethoxy)coumarin)
Summary
Multi-stimuli-responsive gels have attracted particular attention because of their potential for application in highly functionalized materials [1,2,3]. Multi-stimuliresponsiveness has been achieved by combining multiple functional groups that respond to a single stimulus [3]. Copolymer hydrogels of N-isopropylacrylamide (NIPAM) as a temperature-responsive unit and methacrylic acid as a pH-responsive unit are known to be dual-stimuli-responsive gels that respond to temperature and pH [4]. The copolymer hydrogels of NIPAM and acrylic acid can be transformed into PNIPAM-based hydrogels containing pendant crown ether groups by the side-chain reaction of acrylic acid units, and the resulting hydrogels have been applied to lead-sensing materials whose volumes change depending on the Pb2+ concentration [5]. Only a few studies have reported that multi-stimuli-responsiveness is achieved by a single unit responding
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