Abstract
This paper gathered studies on multistimulus-responsive sensing and self-assembly behavior of a novel amphiphilic diblock copolymer through a two-step reverse addition-fragmentation transfer (RAFT) polymerization technique. N-Isopropylacrylamide (NIPAM) macromolecular chain transfer agent and diblock copolymer (poly(NIPAM-b-Azo)) were discovered to have moderate thermal decomposition temperatures of 351.8 and 370.8 °C, respectively, indicating that their thermal stability was enhanced because of the azobenzene segments incorporated into the block copolymer. The diblock copolymer was determined to exhibit a lower critical solution temperature of 34.4 °C. Poly(NIPAM-b-Azo) demonstrated a higher photoisomerization rate constant (kt = 0.1295 s−1) than the Azo monomer did (kt = 0.088 s−1). When ultraviolet (UV) irradiation was applied, the intensity of fluorescence gradually increased, suggesting that UV irradiation enhanced the fluorescence of self-assembled cis-isomers of azobenzene. Morphological aggregates before and after UV irradiation are shown in scanning electron microscopy (SEM) and dynamic light scattering (DLS) analyses of the diblock copolymer. We employed photoluminescence titrations to reveal that the diblock copolymer was highly sensitive toward Ru3+ and Ba2+, as was indicated by the crown ether acting as a recognition moiety between azobenzene units. Micellar aggregates were formed in the polymer aqueous solution through dissolution; their mean diameters were approximately 205.8 and 364.6 nm at temperatures of 25.0 and 40.0 °C, respectively. Our findings contribute to research on photoresponsive and chemosensory polymer material developments.
Highlights
The potential applications for stimulus-responsive polymers have expanded remarkably in recent years and include fluorescent chemosensors, biological probes, and drug delivery vehicles that utilize pH, temperature, light, humidity, electric field, or ionic strength [1,2,3,4,5,6,7]
Two-step reverse addition-fragmentation transfer (RAFT) polymerization techniques were employed in this study to obtain a NIPAM-containing dual-stimulus-responsive diblock copolymer (poly(NIPAM-b-azobenzene monomer (Azo))) with azobenzene units as comonomers
The decomposition temperature (Td ) values of the NIPAM macro-CTA and poly(NIPAM-b-Azo) were 351.8 and 370.8 ◦ C, respectively; this revealed that the thermal stability was enhanced because azobenzene segments were incorporated into the block copolymer
Summary
The potential applications for stimulus-responsive polymers have expanded remarkably in recent years and include fluorescent chemosensors, biological probes, and drug delivery vehicles that utilize pH, temperature, light, humidity, electric field, or ionic strength [1,2,3,4,5,6,7]. Executed studies have employed RAFT and atom transfer radical polymerization techniques to derive azobenzene-containing amphiphilic block copolymers with both the self-assembling characteristics that block copolymers exhibit in solutions and the photoresponsive properties that azobenzene polymers exhibit; the aggregates that were obtained further affected their fluorescence properties [23,24,25,26]. Wang et al [46] prepared a tetraphenylethene-containing poly(NIPAM) exhibiting aggregation-induced emission when assembled into nanoparticles in water, and the fluorescence intensity was lower when the temperature was higher. Two-step RAFT polymerization techniques were employed in this study to obtain a NIPAM-containing dual-stimulus-responsive (i.e., temperature and light) diblock copolymer (poly(NIPAM-b-Azo)) with azobenzene units as comonomers. The addition of the hydrophobic azobenzene unit to poly(NIPAM) induced a microphase separation, which suggests that this polymer may have wide application to rapid microphase separation and high-potential optical response
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