Preparation of Hydrophilic Encapsulated Carbon Nanotubes with Polymer Brushes and Its Application in Composite Hydrogels

Carbon nanotubes can be used as promising reinforcement materials to improve the mechanical properties of hydrogels, but their poor dispersibility in aqueous solution severely limits their application in preparation of composite hydrogels. Therefore, to develop method for modification of carbon nanotubes is still highly desired. In this paper, a facile approach for preparation of the hydrophilic carbon nanotube was reported. The encapsulated multiwalled carbon nanotubes (E-CNT-PAA) with cross-linked shell structure were obatined through the self-assembly of the amphipathic azide diblock copolymers poly­(acrylic acid)-<i>b</i>-poly­(4-vinylbenzyl azide-<i>co</i>-styrene) (PAA-<i>b</i>-(PVBA-<i>co</i>-PS)), and the cross-linking of inside azide groups under UV irradiation. The encapsulated MWCNT was characterized by FT-IR, Raman and TEM. It was demonstrated that the dispersibility of the hydrophilic encapsulated MWCNTs was related to the length of the poly­(acrylic acid) brushes. Subsequently, thermal-responsive composite hydrogels (PNIPAM/E-CNT-PAA) were prepared by in situ polymerization of <i>N</i>-isopropylacrylamide (NIPAM) in the solution of dispersed E-CNT-PAA. The results showed that the composite hydrogels possessed high mechanical properties compared to the pure PNIPAM hydrogel. The tensile strength and elongation of the composite hydrogels were highly dependent on the content of the modified MWCNTs. The composite hydrogels with 0.46 wt % MWCNTs exhibited tensile strength of 97.7 kPa and elongation of 465%, which were at least 3.5× higher than those of the PNIPAM hydrogel. Moreover, the composite hydrogels displayed significant and reversible stimuli-responsiveness

A Diheteroatom Fluoroalkylation Reagent for Preparation of S- and N‑Containing Fluoroalkyl Compounds and Sulfonic Acid Polymer

The first stable diheteroatom fluoroalkylation reagent, 2-((2-azido-1-chloro-1,2,2-trifluoro­ethyl)­thio)­pyrimidine (ACTP), has been prepared by a novel method. By using this reagent, various fluorinated thioethers and sulfones have been successfully prepared. The dearylation and dearylation–oxida­tion of fluoroalkyl 2-pyrimidyl sulfone in one-pot reaction were investigated systematically, and the results demonstrated that both fluoroalkyl sulfinates and sulfonates could be obtained in high yields. In addition, ACTP proved to be useful for the preparation of a fluorinated sulfonic acid proton-exchange membrane

Facile and Highly Efficient Strategy for Synthesis of Functional Polyesters via Tetramethyl Guanidine Promoted Polyesterification at Room Temperature

A facile and highly efficient strategy for the synthesis of functional polyesters from 10-undecenoic acid, which is abundantly available and derived from ricin oil, has been successfully achieved using 1,1,3,3-tetramethyl guanidine (TMG) as a promoter at room temperature. The experimental results indicate that high molecular weight polyesters have been obtained and a variety of functional groups, such as alkenyl, alkynyl, nitro, epoxy, hydroxyl, and bromoisobutyrate, can be incorporated as pendant groups. The structures of the obtained polymers were demonstrated by ¹H and ¹³C NMR spectroscopy and their thermal properties were studied by DSC and TGA

Flavone-Based ESIPT Ratiometric Chemodosimeter for Detection of Cysteine in Living Cells

We have designed and synthesized a novel ratiometric fluorescent chemodosimeter <b>MHF</b>-based ESIPT process for specific detection of cysteine among the biological thiols. The probe <b>MHF</b> shows very weak blue fluorescence under UV excitation. Upon addition of cysteine (Cys), the reaction of Cys with <b>MHF</b> induces acrylate hydrolysis, thereby enabling the ESIPT process to shift the weak blue emission to a strong green emission with about 20-fold enhancement. We utilized ¹H NMR spectra to elucidate the fluorescence sensing mechanism. Moreover, the cellular imaging experiment indicated the <b>MHF</b> possessed excellent selectivity, low cytotoxicity, and desirable cell permeability for biological applications

Novel Reversible Mechanochromic Elastomer with High Sensitivity: Bond Scission and Bending-Induced Multicolor Switching

Although the rational designed mechanochromic polymer (MCP) materials have evoked major interest and experienced significant progress recently, it is still a great challenge to develop a facile and effective strategy for preparation of reversible broad-spectrum MCPs with a combination of wide-range color switch ability and high sensitivity, which thus make it possible to mimic gorgeous color change as in nature. Herein, we designed and synthesized a novel rhodamine-based mechanochromic elastomer. Our results demonstrated that the elastomer exhibited very promising and unique properties. Three primary fluorescence colors were presented during continuous uniaxial extension and relaxing process, and reversible broad-spectrum fluorescence color change could be achieved consequently. The fluorescence quantum yield of the opened zwitterion of this new mechanophore was as high as 0.67. In addition, the elastomer showed very high sensitivity to stress with a detectable activation strain of ∼0.24, which was much smaller than those reported in the previous literature reports. Meantime, the easy-to-obtain material, facile preparation, and good mechanical property also made it suitable for potential practical applications

Novel Reversible Mechanochromic Elastomer with High Sensitivity: Bond Scission and Bending-Induced Multicolor Switching

Although the rational designed mechanochromic polymer (MCP) materials have evoked major interest and experienced significant progress recently, it is still a great challenge to develop a facile and effective strategy for preparation of reversible broad-spectrum MCPs with a combination of wide-range color switch ability and high sensitivity, which thus make it possible to mimic gorgeous color change as in nature. Herein, we designed and synthesized a novel rhodamine-based mechanochromic elastomer. Our results demonstrated that the elastomer exhibited very promising and unique properties. Three primary fluorescence colors were presented during continuous uniaxial extension and relaxing process, and reversible broad-spectrum fluorescence color change could be achieved consequently. The fluorescence quantum yield of the opened zwitterion of this new mechanophore was as high as 0.67. In addition, the elastomer showed very high sensitivity to stress with a detectable activation strain of ∼0.24, which was much smaller than those reported in the previous literature reports. Meantime, the easy-to-obtain material, facile preparation, and good mechanical property also made it suitable for potential practical applications

Preparation of Covalent Pseudo-Two-Dimensional Polymers in Water by Free Radical Polymerization

Two-dimensional (2D) polymer has attracted considerable attention due to its excellent properties. Although a number of 2D polymers have been reported, preparation of free-standing single-layer 2D polymers in solution is still a big challenge. Here we report a facile and highly efficient strategy for synthesis of free-standing single-layer covalent pseudo-2D polymers via free radical polymerization in water on a large scale. The strategy designated as “two-dimensional self-assembly polymerization (2DSP)” includes formation of supramolecular 2D nanosheets by self-assembly of bola-amphiphilic monomer that bearing two maleic acid moieties and transformation of supramolecular 2D nanosheets to covalent pseudo-2D polymers by copolymerization with vinyl monomers. We find that the counterion of the bola-amphiphile has a significant influence on formation of single-layer supramolecular 2D nanosheets, and the formation of 2D polymer sheets is highly related to the vinyl monomers. The unique 2D polymer sheets were used to prepare hydrogels with excellent mechanical properties

Real-Time and in Situ Investigation of “Living”/Controlled Photopolymerization in the Presence of a Trithiocarbonate

Polymerization of methyl acrylate under ultraviolet (UV) irradiation in the presence of <i>S</i>-1-dodecyl-<i>S</i>′-(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (DDMAT) was investigated by in situ ¹H nuclear magnetic resonance spectroscopy. Effects of light intensity, wavelength, and concentration of DDMAT on the polymerization behaviors were studied in detail. The experimental results demonstrate that the “living” features of the photopolymerization are related to the concentration of DDMAT. “Living”/controlled radical polymerization was successfully achieved with a high concentration of DDMAT. However, with a low concentration of DDMAT, the polymerization proceeded in an uncontrolled manner and produced polymers with high molecular weights and broad polydispersities. Photochemical behavior of DDMAT was studied in detail, and the results showed that the photolysis of DDMAT was reversible at high concentration, whereas contrarily, DDMAT decomposed irreversibly at low concentration. A possible mechanism was proposed for the reversible photolysis of DDMAT at high concentration, which may involve both reversible termination and reversible addition–fragmentation chain transfer approaches

Synthesis and Luminescence of POSS-Containing Perylene Bisimide-Bridged Amphiphilic Polymers

A novel well-defined amphiphilic fluorescent polymer containing asymmetric perylene bisimide was designed and synthesized by combining reaction of perylene anhydride with amino functional polyhedral oligomeric silsesquioxane (POSS) and atom transfer radical polymerization (ATRP) of <i>N</i>-isopropylacrylamide (NIPAM). All the intermediate and final products were characterized by NMR, Fourier transform infrared spectroscopy (FT-IR), elemental analyses, and gel permeation chromatograph (GPC). Self-assembly of the amphiphilic polymers was investigated in aqueous solution and POSS-containing hybrid nanoparticles were obtained and characterized by dynamic laser light scattering (DLS) and transmission electron microscopy (TEM). The novel hybrid nanoparticles exhibit attractive high red fluorescence at 645 nm due to the significant effect of the bulky POSS moieties. Moreover, based on the thermoresponsive PNIPAM coronas, the fluorescence intensity of the self-assembled hybrid nanoparticles can be further enhanced and tuned by changing temperature

2,2′-Biimidazole-Based Conjugated Polymers as a Novel Fluorescent Sensing Platform for Pyrophosphate Anion

Three novel conjugated polymers based on 2,2′-biimidazole have been successfully designed and synthesized through the Suzuki coupling reactions, and their fluorescence sensing ability to metal ions and anions was investigated. The emission of the two polymers with hydrophilic side chains can be efficiently quenched by Cu²⁺ through a photoinduced electron transfer process. Moreover, the polymer–Cu²⁺ complexes exhibit excellent “turn on” sensing properties for detection of pyrophosphate (PPi) anion. These complex sensors possess high selectivity avoiding the interference from other anions, very fast response (less than 3 min) to PPi, and the detection limit of about 0.17 ppm. In addition, the linear detection range of PPi can be tuned conveniently by changing the amount of Cu²⁺ ions. Thus, the conjugated polymers can be used as a novel fluorescent sensing platform, and this work provides a new strategy for the development of PPi sensors