Huiqi Zhang

Nankai University, T’ien-ching-shih, Tianjin Shi, China

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Publications (25)112.48 Total impact

  • European Polymer Journal 05/2014; 54:95–108. · 3.24 Impact Factor
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    ABSTRACT: A facile, general, and highly efficient one-pot approach to obtain azobenzene (azo)-containing molecularly imprinted polymer (MIP) nanoparticles with photoresponsive template binding and release properties in aqueous media is described, which involves the combined use of hydrophilic macromolecular chain transfer agent-mediated reversible addition-fragmentation chain transfer precipitation polymerization and easily available water-insoluble azo functional monomers. The resulting azo-containing MIPs were characterized with dynamic laser scattering (DLS), SEM, FTIR, static contact angle and water dispersion studies, and equilibrium binding experiments. They have proven to be nanoparticles (their diameters being around 104–397 nm, as determined by DLS in methanol) with surface-grafted hydrophilic polymer brushes and exhibit excellent pure water-compatible template binding properties. Moreover, obvious photoregulated template binding behaviors were observed for such azo-containing MIP nanoparticles, which led to their largely accelerated template release in the aqueous media under the UV light irradiation. Furthermore, the general applicability of the strategy was also demonstrated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014
    Journal of Polymer Science Part A Polymer Chemistry 04/2014; · 3.54 Impact Factor
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    ABSTRACT: A facile and highly efficient new approach (namely RAFT coupling chemistry) to obtain well-defined hydrophilic molecularly imprinted polymer (MIP) microspheres with excellent specific recognition ability towards small organic analytes in the real undiluted biological samples is described. It involves the first synthesis of "living" MIP microspheres with surface-bound vinyl and dithioester groups via RAFT precipitation polymerization (RAFTPP) and their subsequent grafting of hydrophilic polymer brushes by the simple coupling reaction of hydrophilic macro-RAFT agents (i.e., hydrophilic polymers with a dithioester end group) with vinyl groups on the "living" MIP particles in the presence of a free radical initiator. The successful grafting of hydrophilic polymer brushes onto the obtained MIP particles was confirmed by SEM, FT-IR, static contact angle and water dispersion studies, elemental analyses, and template binding experiments. Well-defined MIP particles with densely grafted hydrophilic polymer brushes (~1.8 chains/nm2) of desired chemical structures and molecular weights were readily obtained, which showed significantly improved surface hydrophilicity and could thus function properly in real biological media. The origin of the high grafting densities of the polymer brushes was clarified and the general applicability of the strategy was demonstrated. In particular, the well-defined characteristics of the resulting hydrophilic MIP particles allowed the first systematic study on the effects of various structural parameters of the grafted hydrophilic polymer brushes on their water-compatibility, which is of great importance for rationally designing more advanced real biological samples-compatible MIPs.
    Biomacromolecules 03/2014; · 5.37 Impact Factor
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    Huiqi Zhang
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    ABSTRACT: As a new class of synthetic receptors, molecularly imprinted polymers (MIPs) have shown great potential in many applications because of their good specific recognition ability, high stability, and easy preparation. The ultimate goal of molecular imprinting is to obtain MIPs that can be routinely used as alternatives to natural antibodies and receptors. However, the presently developed MIPs targeting small organic molecules mostly fail to show specific bindings in aqueous solutions, which is in sharp contrast to biological receptors and significantly limits their practical applications in such areas as biomimetic assays and sensors. Many efforts have been devoted to address this issue in the past two decades. In this feature article, I provide a detailed overview of the progress made in the development of water-compatible MIPs with an emphasis on our strategies to solve this challenging problem. Moreover, some still existing challenges and future prospects in this research area are also presented.
    Polymer 02/2014; 55(3):699–714. · 3.77 Impact Factor
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    ABSTRACT: A facile and highly efficient approach to obtain narrowly dispersed hydrophilic and magnetic molecularly imprinted polymer microspheres with molecular recognition ability in a real biological sample as good as what they show in the organic solvent-based media is described for the first time.
    Chemical Communications 01/2014; · 6.38 Impact Factor
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    ABSTRACT: A new and efficient strategy for obtaining a series of reactive azobenzene (azo)-containing main-chain liquid crystalline polymers (LCPs) is described, which involves the first design and synthesis of acrylate-type azo monomers with different length of flexible spacers and an amino end-group (in its trifluoroacetate salt form) and their subsequent Michael addition polymerization under mild reaction conditions. The resulting polymers showed rather high thermal stability, relatively low glass transition temperatures, a broad temperature range of smectic C liquid crystalline phase, and reversible photoresponsive behavior. The presence of secondary amino groups in the backbones of these azo main-chain LCPs not only made them highly reactive precursors for various new functional linear and cross-linked azo LCPs but also led to the formation of hydrogen-bonding interactions among their polymer chains. Supramolecular hydrogen-bonding cross-linked LCP fibers were directly fabricated by using the simple melt spinning method, which proved to have a high order of mesogen along the fiber axis and exhibit good mechanical properties, fast and reversible photoinduced bending and unbending behaviors, and large photoinduced stress (240 kPa) at close to ambient temperature as well as excellent photodeformation fatigue resistance.
    Macromolecules 09/2013; 46(19):7650–7660. · 5.93 Impact Factor
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    ABSTRACT: A facile, general, and highly efficient approach to prepare uniform core–shell molecularly imprinted polymer (MIP) particles with enzyme inhibition potency is described for the first time, which involves the combined use of molecular imprinting and controlled/“living” radical polymerization (CRP) techniques as well as surface-anchoring strategy. The thickness of the enzyme-imprinted surface layers of the core–shell MIP microspheres had a significant influence on their binding properties, and only those with their thickness comparable with the diameters of the targeted enzymes could afford enzyme-MIPs with optimal specific bindings. The as-prepared enzyme-MIPs were found to have homogeneous binding sites and high template binding capacities, affinity, and selectivity, and they proved to show much higher enzyme inhibition potency than the small inhibitor by 3 orders of magnitude (i.e., the enzyme inhibition constant of every binding site of the MIP microspheres was about one-thousandth of that of the small inhibitor), mainly due to the formation of strong long-range secondary interactions between enzymes and imprinted pockets. In addition, the general applicability of our strategy was confirmed.
    ACS Macro Letters. 06/2013; 2(6):566–570.
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    ABSTRACT: Bisphenol A (BPA) and propranolol-imprinted polymers have been prepared via both reversible addition-fragmentation chain transfer "bulk" polymerization (RAFTBP) and traditional radical "bulk" polymerization (TRBP) under similar reaction conditions, and their equilibrium binding properties were compared in detail for the first time. The chemical compositions, specific surface areas, equilibrium bindings, and selectivity of the obtained molecularly imprinted polymers (MIPs) were systematically characterized. The experimental results showed that the MIPs with molecular imprinting effects and quite fast binding kinetics could be readily prepared via RAFTBP, but they did not show improved template binding properties in comparison with those prepared via TRBP, which is in sharp contrast to many previous reports. This could be attributed to the heavily interrupted equilibrium between the dormant species and active radicals in the RAFT mechanism because of the occurrence of fast gelation during RAFTBP. The findings presented here strongly demonstrates that the application of controlled radical polymerizations (CRPs) in molecular imprinting does not always benefit the binding properties of the resultant MIPs, which is of significant importance for the rational use of CRPs in generating MIPs with improved properties. Copyright © 2013 John Wiley & Sons, Ltd.
    Journal of Molecular Recognition 05/2013; 26(5):240-51. · 3.01 Impact Factor
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    ABSTRACT: The facile and efficient one-pot synthesis of monodisperse, highly crosslinked, and “living” functional copolymer microspheres by the ambient temperature iniferter-induced “living” radical precipitation polymerization (ILRPP) is described for the first time. The simple introduction of iniferter-induced “living” radical polymerization (ILRP) mechanism into precipitation polymerization system, together with the use of ethanol solvent, allows the direct generation of such uniform functional copolymer microspheres. The polymerization parameters (including monomer loading, iniferter concentration, molar ratio of crosslinker to monovinyl comonomer, and polymerization time and scale) showed much influence on the morphologies of the resulting copolymer microspheres, thus permitting the convenient tailoring of the particle sizes by easily tuning the reaction conditions. In particular, monodisperse poly(4-vinylpyridine-co-ethylene glycol dimethacrylate) microspheres were prepared by the ambient temperature ILRPP even at a high monomer loading of 18 vol %. The general applicability of the ambient temperature ILRPP was confirmed by the preparation of uniform copolymer microspheres with incorporated glycidyl methacrylate. Moreover, the “livingness” of the resulting polymer microspheres was verified by their direct grafting of hydrophilic polymer brushes via surface-initiated ILRP. Furthermore, a “grafting from” particle growth mechanism was proposed for ILRPP, which is considerably different from the “grafting to” particle growth mechanism in the traditional precipitation polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
    Journal of Polymer Science Part A Polymer Chemistry 05/2013; 51(9):1983-1998. · 3.54 Impact Factor
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    Huiqi Zhang
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    ABSTRACT: As an emerging new polymerization technique, controlled/“living” radical precipitation polymerization (CRPP) involves the introduction of controlled/“living” radical polymerization (CRP) mechanism into the precipitation polymerization system and can be effectively implemented by simply replacing the initiator normally used in the traditional precipitation polymerization (e.g., azobisisobutyronitrile (AIBN)) with a CRP initiating system. It combines the advantages of the traditional precipitation polymerization and CRP and can thus be performed in a controlled manner without need for any surfactant and stabilizer, leading to the precise control over the sizes, compositions, surface functionalities, and “living” groups of the resulting polymer microspheres. Several CRPP approaches have been developed up to now, including atom transfer radical precipitation polymerization (ATRPP), iniferter-induced “living” radical precipitation polymerization (ILRPP), and reversible addition-fragmentation chain transfer (RAFT) precipitation polymerization (RAFTPP). In this feature article, we provide a detailed overview of these recently developed CRPP approaches and demonstrate their high versatility in the design and synthesis of advanced functional polymers such as uniform, highly crosslinked, and “living” functional polymer microspheres and advanced molecularly imprinted polymers (MIPs) including MIP microspheres with improved binding properties, water-compatible MIP microspheres, and MIP microspheres with stimuli-responsive template binding properties in aqueous media. In addition, some perspectives on this new research area are also presented.
    European Polymer Journal 03/2013; 49(3):579–600. · 3.24 Impact Factor
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    ABSTRACT: In river water, milk, and bovine serum, molecularly imprinted polymer nanoparticles with hydrophilic polymer brushes showed excellent molecular recognition. Readily prepared by precipitation polymerization with a macromolecular chain-transfer agent, such nanoparticles are promising alternatives to antibodies for many applications owing to their superior dispersion and binding properties in biological matrices.
    Angewandte Chemie International Edition 12/2012; · 11.34 Impact Factor
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    ABSTRACT: A facile, general, and highly efficient approach to obtain azobenzene (azo)-containing molecularly imprinted polymer (MIP) microspheres with both photo- and thermoresponsive template binding properties in pure aqueous media is described for the first time, which involves the first synthesis of "living" azo-containing MIP microspheres with surface-immobilized alkyl halide groups via atom transfer radical precipitation polymerization (ATRPP) and their subsequent modification via surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm). The successful grafting of poly(NIPAAm) (PNIPAAm) brushes onto the obtained MIP microspheres was confirmed by FT-IR, SEM, water dispersion stability and static contact angle studies, and template binding experiments. The introduction of PNIPAAm brushes onto the azo-containing MIP microspheres significantly improved their surface hydrophilicity and imparted thermoresponsive properties to them, leading to their pure water-compatible and thermoresponsive template binding properties. In addition, the binding affinity of the imprinted sites in the grafted azo-containing MIP microspheres was found to be photoresponsive toward the template in pure water, and this photoregulation process proved to be highly repeatable under photoswitching conditions.
    Langmuir 05/2012; 28(25):9767-77. · 4.38 Impact Factor
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    ABSTRACT: The synthesis of a series of new photoresponsive side-chain liquid crystalline polymethacrylates with amide group-substituted azobenzene (azo) mesogens and different length of flexible spacers and terminal tails via conventional free radical polymerization is described. The resulting azo polymers proved to have high thermal stability and good solubility in common organic solvents (e.g., tetrahydrofuran and chloroform). Differential scanning calorimetry, polarizing optical microscopy, and small angle X-ray scattering studies confirmed the presence of obvious enantiotropic smectic C liquid crystalline phases (with a bilayer lamellar structure) for all these polymers. The introduction of an amide group into the azo mesogen led to the formation of strong hydrogen bonding among the side chains of the polymers (as revealed by variable temperature FT-IR), which played a decisive role in forming and stabilizing the liquid crystalline mesophases of the polymers. In addition, the length of the flexible spacers and terminal tails also significantly influenced their phase transition behaviors. Furthermore, the photoresponsivity of the polymer solutions was verified and the effects of the molecular structures of the polymers on their photoresponsive properties were also studied.
    Soft Matter 05/2012; 8(20):5532-5542. · 4.15 Impact Factor
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    ABSTRACT: A facile, general, and highly efficient approach to obtain narrowly dispersed molecularly imprinted polymer microspheres with multiple stimuli-responsive template binding properties in aqueous media by successive RAFT polymerization is described.
    Chemical Communications 05/2012; 48(50):6217-9. · 6.38 Impact Factor
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    Angewandte Chemie International Edition 12/2011; 50(49):11731-4. · 11.34 Impact Factor
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    ABSTRACT: The first controlled synthesis of pure water-compatible molecularly imprinted polymer (MIP) microspheres with ultrathin hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) shells (including both PHEMA brushes and lightly crosslinked PHEMA hydrogel layer) via surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization is described. The presence of ultrathin hydrophilic polymer shells on the MIP microspheres was confirmed by SEM, FT-IR, fluorescent labeling treatment, contact angle studies, and water dispersion stability test, and some quantitative information including the thickness of the grafted hydrophilic polymer layers as well as the molecular weights and polydispersities of the grafted polymer brushes and their grafting densities was provided. The facile surface-grafting of both PHEMA brushes and PHEMA hydrogel layer on the MIP microspheres proved to be highly efficient for improving their surface hydrophilicity and suppressing the hydrophobically driven nonspecific interactions between the MIPs and template molecules, leading to MIPs with pure water-compatible binding properties. The findings presented here not only prove the general applicability of the controlled hydrophilic polymer brushes-grafting approach in obtaining pure water-compatible MIPs, but also largely extend the scope of this versatile surface-grafting approach through the controlled surface-grafting of hydrophilic polymer hydrogel layer onto the MIPs. Moreover, the significant effect of the chain length of the grafted polymer brushes and the presence of crosslinking in the grafted polymer shells on the surface hydrophilicity and water-compatibility of the MIP microspheres was also demonstrated for the first time, which is of great importance for the rational design of water-compatible MIPs by using this controlled surface-grafting approach.
    Soft Matter 09/2011; 7(18):8428-8439. · 4.15 Impact Factor
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    ABSTRACT: A facile, general, and efficient one-pot approach to obtaining narrow or monodisperse, highly cross-linked, surface-functionalized, and “living” polymer microspheres with uniformly cross-linked structures by atom transfer radical precipitation polymerization (ATRPP) is described for the first time. The simple introduction of atom transfer radical polymerization (ATRP) mechanism into precipitation polymerization system allows the direct generation of uniformly cross-linked “living” polymer microspheres with their number-average diameters ranging from 0.73 to 3.25 μm and their polydispersity indices being typically lower than 1.01. The polymerization parameters (including stirring rate, monomer loading, initiator and catalyst concentrations, molar ratio of cross-linker to monovinyl functional comonomer, and polymerization scale and time) have proven to show significant influence on the morphologies of the resulting polymer microspheres, which makes it very convenient to control the particle sizes by easily tuning the reaction conditions. The general applicability of ATRPP was demonstrated by synthesizing a series of uniform functional copolymer microspheres with different incorporated functional comonomers (i.e, 4-vinylpyridine, acrylamide, and 2-hydroxyethyl methacrylate). Moreover, the “livingness” of the resulting polymer microspheres was confirmed by their direct grafting of hydrophilic polymer brushes via surface-initiated ATRP under mild reaction conditions. Furthermore, a “grafting from” particle growth mechanism is proposed for ATRPP, which is considerably different from the “grafting to” particle growth mechanism in the traditional precipitation polymerization.
    RSC Advances 07/2011; 2(13). · 3.71 Impact Factor
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    ABSTRACT: The first successful preparation of azobenzene (azo)-containing molecularly imprinted polymer (MIP) microspheres with photoresponsive template binding properties is described. A methacrylate azo functional monomer with a pyridinegroup was used for this purpose, and its good solubility in acetonitrile allowed the implementation of molecular imprinting via precipitationpolymerization, leading to azo-containing MIP microspheres (number-average diameter = 1.33 μm, polydispersity index = 1.15) with obvious molecular imprinting effects towards the template 2,4-dichlorophenoxyacetic acid (2,4-D), rather fast template rebinding kinetics, and appreciable selectivity over structurally related compounds. The binding association constant Ka and apparent maximum number Nmax for high-affinity sites of the imprinted polymer in the dark environment were determined by Scatchard analysis to be 2.3 × 104 M−1 and 10.0 μmol g−1, respectively. Most importantly, the binding affinity of the imprinted sites in azo-containing MIP microspheres was found to be photoresponsive towards the template, which decreased upon UV light irradiation (as revealed by the resulting lower Ka value for high-affinity sites and reduced specific bindings), whereas it could be recovered during the subsequent thermal (or visible light-induced) back-isomerization. Furthermore, this photoregulation process proved to be highly repeatable under photoswitching conditions.
    Journal of Materials Chemistry 02/2011; 21(7):2320-2329. · 5.97 Impact Factor
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    ABSTRACT: A new and efficient approach to obtaining molecularly imprinted polymers (MIPs) with both pure water-compatible (i.e., applicable in the pure aqueous environments) and stimuli-responsive binding properties is described, whose proof-of-principle is demonstrated by the facile modification of the preformed MIP microspheres via surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAAm). The presence of poly(NIPAAm) (PNIPAAm) brushes on the obtained MIP microspheres was confirmed by FT-IR as well as the water dispersion and static contact angle experiments, and some quantitative information including the molecular weights and polydispersities of the grafted polymer brushes, the thickness of the polymer brush layers, and their grafting densities was provided. In addition, the binding properties of the ungrafted and grafted MIPs/NIPs in both methanol/water (4/1, v/v) and pure water solutions were also investigated. The introduction of PNIPAAm brushes onto the MIP microspheres has proven to significantly improve their surface hydrophilicity and impart stimuli-responsive properties to them, leading to their pure water-compatible and thermo-responsive binding properties. The application of the facile surface-grafting approach, together with the versatility of RAFT polymerization and the availability of many different functional monomers, makes the present methodology a general and promising way to prepare water-compatible and stimuli-responsive MIPs for a wide range of templates.
    Biosensors & Bioelectronics 11/2010; 26(3):976-82. · 6.45 Impact Factor
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    ABSTRACT: This article describes for the first time the development of a new polymerization technique by introducing iniferter-induced “living” radical polymerization mechanism into precipitation polymerization and its application in the molecular imprinting field. The resulting iniferter-induced “living” radical precipitation polymerization (ILRPP) has proven to be an effective approach for generating not only narrow disperse poly(ethylene glycol dimethacrylate) microspheres but also molecularly imprinted polymer (MIP) microspheres with obvious molecular imprinting effects towards the template (a herbicide 2,4-dichlorophenoxyacetic acid (2,4-D)), rather fast template rebinding kinetics, and appreciable selectivity over structurally related compounds. The binding association constant Ka and apparent maximum number Nmax for the high-affinity sites of the 2,4-D imprinted polymer were determined by Scatchard analysis and found to be 1.18 × 104 M−1 and 4.37 μmol/g, respectively. In addition, the general applicability of ILRPP in molecular imprinting was also confirmed by the successful preparation of MIP microspheres with another template (2-chloromandelic acid). In particular, the living nature of ILRPP makes it highly useful for the facile one-pot synthesis of functional polymer/MIP microspheres with surface-bound iniferter groups, which allows their direct controlled surface modification via surface-initiated iniferter polymerization and is thus of great potential in preparing advanced polymer/MIP materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3217–3228, 2010
    Journal of Polymer Science Part A Polymer Chemistry 06/2010; 48(15):3217 - 3228. · 3.54 Impact Factor

Publication Stats

86 Citations
112.48 Total Impact Points

Institutions

  • 2009–2014
    • Nankai University
      • • College of Chemistry
      • • Department of Chemistry
      T’ien-ching-shih, Tianjin Shi, China