Competitive Molecular‐/Ion‐Recognition Responsive Characteristics of Poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) Copolymers with Benzo‐12‐crown‐4 as Both Guest and Host Units

Abstract

Novel dual molecular- and ion-recognition responsive poly(N-isopropylacrylamide-co-benzo-12-crown-4-acrylamide) (PNB12 C4 ) linear copolymers with benzo-12-crown-4 (B12C4) as both guest and host units are prepared. The copolymers exhibit highly selective sensitivities toward γ-cyclodextrin (γ-CD) and Na(+) . The presence of γ-CD induces the lower critical solution temperature (LCST) of PNB12 C4 copolymer to shift to a higher value due to the formation of 1:1 γ-CD/B12C4 host-guest inclusion complexes, while Na(+) causes a negative shift in LCST due to the formation of 2:1 "sandwich" B12C4/Na(+) host-guest complexes. Regardless of the complexation order, when γ-CD and Na(+) coexist with PNB12 C4 , competitive complexation actions of B12C4 as both guest and host units toward γ-CD and Na(+) finally form equilibrium 2:2:1 γ-CD/B12C4/Na(+) composite complexes, and the final LCST values of PNB12 C4 copolymer reach almost the same level. The results provide valuable guidance for designing and applying PNB12 C4 -based smart materials in various applications.

Gamma‐Cyclodextrin‐Recognition‐Responsive Characteristics of Poly(N‐isopropylacrylamide)‐Based Hydrogels with Benzo‐12‐crown‐4 Units as Signal Receptors

“…N ‐isopropylacrylamide (NIPAM, Sigma‐Aldrich) was recrystallized with a mixture of acetone and hexane . Benzo‐12‐crown‐4‐acrylamide (B12C4Am) was synthesized from benzo‐12‐crown‐4 (B12C4, TCI) . 2,2′‐Azobis(2‐methylpropionamidine) dihydrochloride (V50, Qingdao Runxing Photoelectric Materials) was recrystallized with ethanol.…”

“…Combining the ion‐recognition ability of crown ether units and thermo‐induced volume change behavior of PNIPAM polymers, several kinds of ion‐responsive hydrogels have been developed . Except the ion‐recognition abilities, crown ethers can also act as guest molecules to be captured by some macrocycle molecules . However, up to now, a majority of researches have been focused on the ion‐responsive hydrogels with crown ethers as host molecules; while molecular‐responsive hydrogels using crown ethers as guest molecules have not been reported yet.…”

“…Cyclodextrins are a kind of well‐known host molecules in supramolecular chemistry, which display unique inclusion complexation capacity toward guest molecules . It has been reported that 12‐crown‐4 (12C4), which is one of the most common crown ethers, can not only serve as host molecule to recognize Na + ion, but also act as guest molecule to be selectively captured by γ‐cyclodextrin (γ‐CD) by forming stable 1:1 γ‐CD/12C4 inclusion complexes . Therefore, it can be imagined that, hydrogels with γ‐CD‐recognition‐responsive characteristics can be designed by incorporating 12C4 units into PNIPAM‐based hydrogel networks.…”

“…Therefore, it can be imagined that, hydrogels with γ‐CD‐recognition‐responsive characteristics can be designed by incorporating 12C4 units into PNIPAM‐based hydrogel networks. Recently, Wang et al developed a novel γ‐CD‐responsive linear copolymer with benzo‐12‐crown‐4 (B12C4) as the signal receptor . The copolymer exhibits high sensitivity and selectivity toward γ‐CD, which results in distinct increase of hydrophilicity due to the formation of stable B12C4/γ‐CD inclusion complexes .…”

A Novel Poly(N‐Isopropylacrylamide‐co‐acryloylamidobenzo‐12‐crown‐4) Microgel with Rapid Stimuli‐Responsiveness for Molecule‐Specific Adsorption of γ‐Cyclodextrin

“…First, poly( N ‐isopropylacrylamide‐ co ‐acrylic acid) (PNA) microgels are synthesized by precipitation copolymerization, and then the microgels are further modified by benzo‐12‐crown‐4 (B 12 C 4 ) units via condensation reaction. The crown ether units of B 12 C 4 receptors selectively conjugate γ‐CD molecules . By γ‐CD molecular adsorption to enhance the hydrophilicity of PNB microgels, the microgels exhibit a significant isothermal increase of the volume (Figure ).…”