We herein report on the synthesis and characterization of materials featuring a dual-responsive copolymer segment consisting of photo-responsive spiropyran (SPA) and temperature-responsive triethylene glycol acrylate (TEGA).
We present the synthesis and solution properties of dual stimuli-responsive poly(
N
-isopropylacrylamide-
co
-spiropyran acrylate) (P(NIPAAm-
co
-SPA)) copolymers of varying composition prepared
via
nitroxide-mediated copolymerization. The resulting copolymers feature molar masses from 40,000 to 100,000 g/mol according to static light scattering and an SPA content of up to 5.3%. The latter was determined by
1
H NMR spectroscopy and UV–Vis spectroscopy. These materials exhibit reversible response upon irradiation in polymeric films for a minimum of three cycles; their response in solution to both light and temperature was also investigated in an aqueous TRIS buffer (pH 8). Irradiation was carried out using LED setups with wavelengths of 365 and 590 nm. In aqueous solution, a custom-made setup using a fiber-coupled 200 W Hg(Xe) lamp with 340 and 540 nm filters was used and additional heating of the copolymer solutions during irradiation allowed to study influence of the presence of either the spiropyran or merocyanine form on the cloud point temperature. Hereby, it was found that increasing the SPA content leads to a more pronounced difference between both states and decreasing cloud points in general.
This review focuses on block copolymers featuring different photo-responsive building blocks and self-assembly of such materials in different selective solvents. We have subdivided the specific examples we selected: (1) according to the wavelength at which the irradiation has to be carried out to achieve photo-response; and (2) according to whether irradiation with light of a suitable wavelength leads to reversible or irreversible changes in material properties (e.g., solubility, charge, or polarity). Exemplarily, an irreversible change could be the photo-cleavage of a nitrobenzyl, pyrenyl or coumarinyl ester, whereas the photo-mediated transition between spiropyran and merocyanin form as well as the isomerization of azobenzenes would represent reversible response to light. The examples presented cover applications including drug delivery (controllable release rates), controlled aggregation/disaggregation, sensing, and the preparation of photochromic hybrid materials.
A dual
photo- and pH-responsive spirooxazine-functionalized polymer
was synthesized by functionalization of dextran with a spirooxazine
derivative (SO-COOH). The functionalized dextran derivatives can form
nanoparticles in aqueous medium. Under UV light irradiation, the spirooxazine-functionalized
dextran (Dex-SO) nanoparticles isomerize to zwitterionic merocyanine-functionalized
dextran (Dex-MC), which leads to aggregation. However, the process
is reversible upon irradiation with visible light. Under acidic conditions,
the hydrophobic spirooxazine is protonated, and the nanoparticles
aggregate or swell at pH values of 5 or 3, respectively. The encapsulation
of the hydrophobic fluorescent dye Nile Red as model drug allowed
us to gain more information about the structural changes under stimulation
of UV light and acid treatment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.