Triply‐responsive (thermo/light/pH) copolymeric hydrogel of N‐isopropylacrylamide with an azobenzene‐containing monomer

Abstract

A series of triply-responsive copolymer hydrogel was firstly synthesized via free radical polymerization of N-isopropylacrylamide, 4-[(4-(acryloyloxy)ethoxy) phenylazo]benzoic acid (AEPAZA), a water-soluble azobenzene-containing comonomer, and crosslinker. The properties of the hydrogel were subsequently investigated by UV-Vis absorption spectrometry, differential scanning calorimetry, and gravimetry. UV-Vis spectra showed that the copolymer hydrogel had a reasonable tran-cis photoisomerization rate upon UV irradiation and a relatively slow recovery rate in dark. The critical solution temperature (CST) of the copolymer hydrogel decreased with increasing of AEPAZA content and subsequently shifted higher value after UV irradiation. Meanwhile, the phase transitions profile became slower and broader with the incorporation of AEPAZA, which could be partly counterbalanced by UV irradiation. The CST could also be affected by the pH value of buffer solution. In addition, equilibrium swelling behavior clearly showed that the swelling ratio could be modulated by temperature, light, and pH. These stimuli-responsive properties should be very important for controlled release delivery system.

Development of dual-sensitive smart polymers by grafting chitosan with poly (<italic>N</italic>-isopropylacrylamide): an overview

“…In order to improve and increase their applicability, several smart polymers have been developed to combine two or more mechanisms of responsiveness in only one material [41,42] . A quite common approach involves preparing polymers sensible to both temperature and pH stimuli [43][44][45][46][47][48][49][50][51][52][53][54][55] , since they are typical variables parameters in biological and chemical systems, and they can also be easily controlled in vitro and in vivo conditions [56][57][58][59] .…”

Multi-Stimuli-Responsive Polymer Materials: Particles, Films, and Bulk Gels

“…Photo‐, thermo‐ and pH‐responsive PNIPAM‐allylamine copolymer microgels coupled with spiropyran photochromes were synthesized by Garcia et al, the swelling capability of which exhibited multi‐stimuli responsiveness as revealed by dynamic light scattering 162. Triply responsive (light/pH/T) hydrogels could be synthesized via free‐radical polymerization of N ‐isopropylacrylamide and 4‐[(4‐(acryloyloxy)ethoxy)phenylazo]benzoic acid, an azobenzene‐containing monomer, and crosslinker 163. Recently, uniform multi‐stimuli‐responsive hydrogel photonic crystal microparticles (HPCMs) with inverse‐opal structure were generated through a combination of microfluidic and templating techniques by Zhu et al Temperature‐ and pH‐responsive HPCMs were firstly prepared by copolymerizing N ‐isopropylacrylamide and methacrylic acid, which not only showed tunable color variation almost covering the entire wavelength range of visible light by simply tailoring temperature or pH value of the solution, but also displayed rapid response (less than 1 min) due to the small volume and well‐ordered porous structure.…”

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

“…On the one hand, azobenzenes are strongly hydrophobic moieties that can reduce water solubility markedly when incorporated even in small amounts 16, 27. On the other hand, the photoinduced changes in the LCST between the polymers bearing azobenzenes in the trans ‐ and in the cis ‐state, respectively, vary between marked to very weak, without following an obvious rational 8, 14–30. Whereas, for instance, Ishii et al24 did not observe any changes of the cloud points (CPs) upon irradiation of azobenzene end‐capped PNIPAM, Shimoboji et al28 as well as Akiyama and Tamaoki18 reported a temperature difference between the cloud points of the trans ‐ and the cis ‐forms ($ \Delta T_{\rm CP}^{cis-trans} $ ) of up to 10 °C.…”