We report the ultrastiff and tough poly­(acrylamide-co-acrylic acid)/Na-alginate/Fe3+ (P­(AM-co-AA)/Na-alginate/Fe3+) hydrogel via the formation of hybrid ionic–hydrogen bond cross-linking networks. The optimal P­(AM-co-AA)/Na-alginate/Fe3+ hydrogel possessed super high elastic modulus (∼24.6 MPa), tensile strength (∼10.4 MPa), compression strength (∼44 MPa), and toughness (∼4800 J/m2). The P­(AM-co-AA)/Na-alginate/Fe3+ hydrogel was highly stable and maintained its superior mechanical properties in 0.5–2 M NaCl solution, aqueous solution with pH ranging from 4 to 10. The ionic cross-linking networks of the P­(AM-co-AA)/Na-alginate/Fe3+ hydrogels can be locally and selectively dissociated by treating with aqueous NaOH solution with pH of 13 for 1 min and reformed by locally adding the additional Fe3+ solutions, making the hydrogels healable and cohesive. The healed hydrogels from the cutting surfaces can bear a tensile strength of up to 7.1 MPa. Various complex hydrogel structures can be constructed by using the P­(AM-co-AA)/Na-alginate/Fe3+ hydrogels as building blocks via the adhesion of as-prepared hydrogels.

The reactivity of catechols with radicals was applied for the first time to synthesize cross-linked nanostructures, i.e. microgels, without addition of any other cross-linker. Stable microgels with narrow size distribution were successfully obtained via surfactant free emulsion polymerization (SFEP) of acrylamide-type main monomers, namely, acrylamide (AM), N,N-dimethyl­acrylamide (DMAA), N-vinyl­pyrrolidone (NVP), N-vinyl­caprolactam (VCL), N-isopropyl­acrylamide (NIPAM), and (dimethylamino)­propyl­methacrylamide (DMAPM), and vinyl comonomer bearing unprotected catechol in aqueous solution at 70 °C. The formation mechanism of cross-linking network structures was mainly attributed to the reactions between unprotected catechol groups of polymer chains and the radicals of propagating chains during SFEP. With catechol chemistry, microgels with fully water-soluble polymers as scaffolds were achieved without using any surfactant stabilizer.

We studied the aggregation-induced emission (AIE) phenomenon in a nanoconfined environment, where the AIE-active molecule, namely, 1,1,2,2-tetrakis(4-methanoylphenyl)ethane (TPE-4ALD), was held in space via four acylhydrazone bonds within the thermosensitive microgel networks. The thermosensitive microgels, namely N-AH-TPE, were synthesized via the copolymerization of N-isopropylacrylamide (NIPAM) and 4-acylhydrazine-(2-hydroxy-3-(methacryloxypropyl)pyridine hydrochloride (AH monomer) with TPE-4ALD as cross-linker via surfactant free emulsion polymerization (SFEP) in aqueous solution at 70 °C. Acylhydrazone-bonded tetraphenylethene (TPE-4AH) moieties were thus constructed and worked as the fluorophore in N-AH-TPE microgels. The aqueous suspensions of N-AH-TPE microgels exhibit strongly bluish-green fluorescence under ultraviolet excitation because the four arms of TPE-4AH moieties were held and their intramolecular motions are strongly restricted. It is estimated that there is one TPE-4AH moiety per about 394 nm 3 for the swollen N-AH-TPE microgels. The fluorescent properties of N-AH-TPE microgels can be modulated via the change of hydrophilic and hydrophobic environments of TPE-4AH moieties exerted by external stimuli, like addition of various good solvents for TPE-based structures, i.e., N,N-dimethylformamide (DMF), methanol, ethanol, tetrahydrofuran (THF), and N,Ndimethyl sulfoxide (DMSO), varying the solution temperature as well as the counteranions of the microgels. An unusual enhancement in the fluorescent intensity is observed when specific amounts of organic solvent are added into the aqueous suspensions of N-AH-TPE microgels, which can be attributed to the cononsolvency of the polyNIPAM network chains. The shrinkage of N-AH-TPE microgels caused by the cononsolvency effect further strengthens the confinement of TPE-4AH moieties and hence enhances the fluorescent emission of the microgels even though the organic solvents added are good solvents for TPE-4AH. Increasing the solution temperature of N-AH-TPE microgels or introducing hydrophobic counteranions into the microgels also significantly enhances the fluorescent emission of the microgels.

Tetra(4-pyridyl)porphyrin (TPyP)-functionalized thermosensitive ionic microgels (TPyP5-MGs) were synthesized by a two-step quaternization method. The obtained TPyP5-MGs have a hydrodynamic radius of about 189 nm with uniform size distribution and exhibit thermosensitive character. The TPyP5-MG microgel suspensions can optically respond to trace Pb ions in aqueous solution with high sensitivity and selectivity over the interference of other 19 species of metal ions (Yb, Gd, Ce, La, Bi, Ba, Zn, Ni, Co, Mn, Cr, K, Na, Li, Al, Cu, Ag, Cd, and Fe) by using UV-visible spectroscopy. The sensitivity of TPyP5-MGs toward Pb can be further improved by increasing the solution temperature. The limit of detection for TPyP5-MG microgel suspensions in the detection of Pb in aqueous solution at 50 °C is about 25.2 nM, which can be further improved to be 5.9 nM by using the method of higher order derivative spectrophotometry and is much lower than the U. S. EPA standard for the safety limit of Pb ions in drinking water. It is further demonstrated that the TPyP5-MG microgel suspensions have a potential application in the detection of Pb in real world samples, which give consistent results with those obtained by elemental analysis.

Because long cylindrical crystalline micelles of block copolymers (BCPs) are similar to the fibril structures related to some severe diseases to some extent, study of the disassembly process of crystalline micelles of BCPs may provide some conceptual inspiration to the therapy of these diseases. Herein the effect of amines on the fragmentation of cylindrical crystalline-polyelectrolyte polyethylene-block-poly­(acrylic acid) (PE-b-PAA) micelles is investigated. It is found that long crystalline cylindrical micelles (150–400 nm) can be fractured into short stublike ones (20–50 nm) by adding monoamines like diethylamine, triethylamine, and lysine, while addition of diamines such as ethylenediamine and 2,2′-(ethylenedioxy)­di­(ethylamine) or inorganic base like ammonia and sodium hydroxide has little effect on the morphology of cylindrical PE-b-PAA micelles. Fourier transform infrared (FT-IR) characterization shows that the interaction between PAA and amines is electrostatic attraction. The fragmentation of PE-b-PAA cylindrical micelles can be ascribed to the stress release of PAA corona chains swollen by amines, which is related to the effective functionality and molecular size of amines. Calculation of free energy verifies the thermodynamic accessibility of the fragmentation of PE-b-PAA cylindrical crystalline micelles induced by monoamines.