Lianying Liu

Beijing University of Chemical Technology, Peping, Beijing, China

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Publications (26)90.73 Total impact

  • Wenchao Ma · Dong Chen · Lianying Liu · Yuhong Ma · Li Wang · Changwen Zhao · Wantai Yang ·
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    ABSTRACT: A new strategy is developed to prepare both α,ω-dithiol and α,ω-divinyl linear telechelic polythiolether oligomers by visible light induced thiol-ene chemistry in the presence of a fac-Ir(ppy)3 photoredox catalyst. Polythiolether oligomers of well-defined end groups and controlled molecular weights have been successfully synthesized at varying monomer molar ratios of 1,4-benzenedimethanethiol (BDMT) to diethylene glycol divinyl ether (DEGVE). 1H NMR and MALDI-TOF MS analyses demonstrate that as-prepared polythiolethers possess high end-group fidelity, which is further supported by the successful polyaddition of polythiolethers bearing α,ω-dithiol and α,ω-divinyl groups. For example, with the α,ω-dithiol- (Mn = 1900 g mol−1, PDI = 1.25) and α,ω-divinyl-terminated (Mn = 2000 g mol−1, PDI = 1.29) polythiolethers as macromonomers, the molecular weight of resulting polythiolether is up to 7700 g mol−1 with PDI as 1.67. The reactivity of the terminal thiol group is further confirmed by the addition reaction with N-(1-pyrenyl)maleimide. UV-vis spectra and fluorescene measurements suggest that fac-Ir(ppy)3 undergo a redox quenching process reacted with BDMT to generate thiyl free radicals. With these results, the mechanism of the thiol-ene reaction catalyzed by photoredox catalyst is proposed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015
    Journal of Polymer Science Part A Polymer Chemistry 09/2015; DOI:10.1002/pola.27906 · 3.11 Impact Factor
  • Yanan Liu · Yuhong Ma · Lianying Liu · Wantai Yang ·
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    ABSTRACT: Preparation of anisotropic particles based on seed phase separation involves multiple processes, and asymmetrical structures and surfaces cannot be produced when anisotropic shapes emerge. In conventional one-pot dispersion polymerization (Dis.P) using cross-linker, only spherical particles are prepared due to rapid and high cross-linking. Herein, monodisperse snowman-like particles with core–shell/hollow structures and partially rough surface were synthesized straightforward by a modified one-pot Dis.P, in which ethylene glycol and water (6/4, vol.) were used as medium, and ammonium persulfate (APS) aqueous solution, vinyl acetate (VA) and/or acrylic acid (AA), divinylbenzene (DVB) and styrene (St) were added at 6 h. The cross-linking of growing particles was confined to exterior (forming cross-linked shell), and gel contents were low, leading to phase separation. Asymmetrical morphologies, structures, sizes and surface roughness were flexibly tuned by varying amounts of APS, VA and/or AA, water and DVB, and DVB adding speed. At low APS contents or high DVB amounts, the inhomogeneous cross-linking of head enabled its phase to separate, producing elongated head. With addition of VA and AA, phase separations inside head and body were induced, generating hollow structure. Adding DVB very slowly, nonlinear growth of third compartment occurred, forming bowed head.
    Journal of Colloid and Interface Science 05/2015; 445. DOI:10.1016/j.jcis.2014.12.087 · 3.37 Impact Factor
  • Qian Liu · Lianying Liu · Yuhong Ma · Changwen Zhao · Wantai Yang ·
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    ABSTRACT: A new polymer chain growth mode, having multiple potential chain propagation sites, initiated by oligomer of α-methylstyrene (AMS) and styrene (St) (PAS) is presented in this article. The effects of PAS content, AMS fraction in PAS and reaction temperature on bulk polymerization of St have been investigated. It is demonstrated that the PAS performed as macroinitiator in the polymerization of St. The average molecular weights of products increase significantly with the evolution of the polymerization, which is different from conventional free radical polymerization. With 20 wt % macroinitiator, the molecular weights increase from 1.21 × 105 to 3.00 × 105 with the monomer conversion increasing from 15.3 to 83.0%. This unique feature is tentatively attributed to both the reversible polymerization–depolymerization of AMS segments at high temperature which could generate more than one propagation sites in a polymer chain and the combination termination of St free radical polymerization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41460.
    Journal of Applied Polymer Science 02/2015; 132(7). DOI:10.1002/app.41460 · 1.77 Impact Factor
  • Yanan Liu · Wang Liu · Yuhong Ma · Lianying Liu · Wantai Yang ·
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    ABSTRACT: Previously, synthesis of anisotropic particles by seeded polymerizations involves multiple process steps. In conventional one-pot dispersion polymerization (Dis.P) with a cross-linker added, only spherical particles are produced due to rapid and high cross-linking. In this article, a straightforward one-pot preparation of monodisperse anisotropic particles with tunable morphology, dimensions, surface roughness and asymmetrically distributed functional groups is described. With a cross-linker of divinylbenzene (DVB, 8%), ethyleneglycol dimethacrylate (EGDMA, 6%) or dimethacryloyloxybenzophenone (DMABP, 5%) added at 40 min, shortly after the end of nucleation stage in Dis.P of styrene (St) in methanol and water (6/4, vol.), the swollen growing particles are inhomogeneously cross-linked at first. Then, at low gel contents of 59%, 49% and 69%, corresponding to the cases using DVB, EGDMA and DMABP, respectively, the growing particle phase separates and snowman- or dumbbell-like particles are generated. Thermodynamic and kinetic analyses reveal that moderate cross-linking and sufficient swelling of growing particles determine the formation and growth of anisotropic particles during polymerization. Morphology, surface roughness, sizes and cross-linking degrees of each domain of final particles are tuned continuously by varying start addition time and contents of cross-linkers. The snowman-like particles fabricated with DVB have a gradient cross-linking and asymmetrical distribution of pendant vinyl groups from their body to head. The dumbbell-like particles prepared using DMABP have only one domain cross-linked, i.e., only one domain contains photosensitive benzophenone (BP) groups. Adding glycidyl methacrylate (GMA) or propargyl methacrylate (PMA) together with DVB or EGDMA, epoxy or alkynyl groups are asymmetrically incorporated. With the aid of these functional groups, carboxyl, amino or thiol group, and PEG (200) are attached by thiol-ene (yne) click and photocoupling reactions.
    Langmuir 12/2014; 31(3). DOI:10.1021/la504317m · 4.46 Impact Factor
  • Qian Liu · Lianying Liu · Yuhong Ma · Changwen Zhao · Wantai Yang ·
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    ABSTRACT: A new visible light-induced controlled radical polymerization of methacrylate with perfluoro-1-iodohexane (CF3(CF2)5I) as the initiator in the presence of a photoredox catalyst (fac-[Ir(ppy)3]) was developed. Mechanistically, a photoexcited fac-[Ir(ppy)3]* complex reacted with dormant C-I species to generate the chain propagating radical and IrIVI complex, which could be reversibly reduced by the propagating radical. The molecular weight (Mn) and the corresponding distribution index (Mw/Mn = 1.4) were controlled in the polymerization of methyl methacrylate (MMA). For the polymerization of functional monomers, such as glycidyl methacrylate (GMA) and trifluoroethyl methacrylate, their monomer conversions could be up to 96 and 94%, respectively. No polymerization reaction took place without external light stimulation, indicating that the system was an ideal photo “on−off” switchable system. Furthermore, a clean diblock copolymer PMMA-b-PGMA was successfully synthesized with PMMA-I as the macroinitiator. With CF3(CF2)5I as the initiator, short CF3(CF2)5− group tags were introduced on the produced polymer chains. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014
    Journal of Polymer Science Part A Polymer Chemistry 09/2014; 52(22). DOI:10.1002/pola.27390 · 3.11 Impact Factor
  • Haochuan Chen · Changwen Zhao · Ruibo Li · Yuhong Ma · Lianying Liu · Wantai Yang ·
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    ABSTRACT: A novel strategy, based on surface‐initiated grafting polymerization and post‐polymerization thiol‐yne click chemistry, with Ir(ppy)3 as a sole photoredox catalyst, under visible light irradiation is developed. The “livingness” of the grafting polymerization is demonstrated by the linear increase of the graft yield with irradiation time and the block grafting polymerization. Then, acetenyl groups of poly(propargyl methacrylate) (PPMA) grafting chains are reacted with pentaerythritoltetra‐(3‐mercaptopropionate) via the thiol‐yne click reaction. The successful introduction of reactive thiol groups onto the low‐density polyethylene‐graft‐poly(propargyl methacrylate) (LDPE‐g‐PPMA) films is demonstrated by Fourier transform IR (FTIR) and X‐ray photoelectron spectra (XPS) spectroscopy, and the thiol‐ene click reaction with N‐(1‐pyrenyl) maleimide. With tris(2‐phenylpyridine)iridium (Ir(ppy)3) as a photoredox catalyst, visible‐light‐induced surface‐initiated controlled grafting polymerization and thiol‐yne click chemistry are exploited to functionalize a polymer substrate. This technology offers a robust tool to attach a high concentration of desired functional groups onto the surface of polymeric materials.
    Macromolecular Chemistry and Physics 07/2014; 215(14). DOI:10.1002/macp.201400172 · 2.62 Impact Factor
  • Yanan Liu · Qing Yang · Jinmei Zhu · Lianying Liu · Wantai Yang ·
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    ABSTRACT: Preparation of anisotropic particles based on phase separation of prefabricated seeds in polymerizations generally involves multiple process steps. In conventional one-pot dispersion polymerization, only spherical particles are produced. Herein, anisotropic particles with asymmetrical core-shell structure, multiple compartments, and continuously tunable surface roughness and sizes were synthesized by a modified one-pot dispersion polymerization. A mixture of polar solvents, ethylene glycol (EG), and water (6/4, vol.) was used as medium for polymerization of styrene (St). In the presence of ammonium persulfate (APS) and vinyl acetate (VA), divinylbenzene (DVB, 16.1–66.4 %) and (St, 50.3–0 %) were added at 60, 180, and 360 min, respectively. Dense cross-linking was confined to exterior of swollen growing particles, resulting in phase separation and formation of snowman-like particles with coarse, core-shell structured body, and smooth, no or partially cross-linked head. The newly formed compartments were also inhomogeneously cross-linked and their phases separated, producing three and four compartment anisotropic particles with an aspect ratio up to 2.3. Gel content of final particles was less than 75 %. Due to a sequential cross-linking from growing particle to newly formed compartments, reaction stability and particle monodispersity were maintained even when high amounts of DVB were added. Asymmetrical morphologies, structures, sizes, and surface roughness of particles were continuously tuned by varying DVB amount and its start addition time. This one-pot method provides a simple, efficient route for synthesis of anisotropic particles.
    Colloid and Polymer Science 02/2014; 293(2):523-532. DOI:10.1007/s00396-014-3444-0 · 1.87 Impact Factor
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    ABSTRACT: Due to the steric hindrance effects in combination with stability of the tertiary benzylic alpha-methylstyryl radical, there is a dynamic equilibrium between the monomer alpha-methylstyrene (AMS) and its polymer (PAMS) when the temperature is greater than 61 degrees C (the ceiling polymerization temperature). Based on this unique feature, a novel strategy to prepare copolymers of AMS having liable bonds as potential macromolecular free radical initiators for synthesizing block and graft copolymers has been successfully developed in our laboratory. By conventional free radical polymerization, a series of AMS copolymers, including copolymers with (meth)acrylate, acrylic acid, styrene and maleic anhydride were synthesized. Typically, with the increasing of AMS fraction in monomer feed, the rate of copolymerization was significantly retarded and the molecular weight of the copolymers was reduced. However, the copolymer yield could be as high as 90% (w) with the increased addition of initiator, up to 4% (w), and the molar fraction of AMS structural unit in AMS copolymers could be up to 25% (mol%). It has been demonstrated that the copolymers containing AMS structural units are efficient free radical initiators when the temperature is greater than 80 degrees C (much better higher than 90 degrees C). These copolymers could be exploited as macroinitiator in preparing block copolymers and core-shell polymer particles by bulk, solution and emulsion polymerization processes. In addition, the experimental results demonstrated that the molecular weight of copolymer products prepared with AMS copolymers as macromolecular initiators increased steadily with the monomer conversion. Though the polymerization initiated by AMS copolymers was not a well-controlled living system yet, it showed some characteristics of living polymerization. The ESR spectrum presented direct evidence of the generation of carbon centered radicals in the products of copolymer of AMS with glycidyl methacrylate (PAG) heated with N-t-butyl-alpha-phenylnitrone at 90 degrees C in toluene. Besides initiating the polymerization of vinyl monomer to prepare diblock copolymer, the AMS copolymers offered a practical pathway to synthesize grafting polymers in melting state. For example, with the addition of PAG in the PP/Nylon melten blending, it has been demonstrated a significant in situ compatibilization effect and the formation of graft polymer of PAG and PP. Furthermore, the AMS copolymers could also be used to modify MWCNT by free radical grafting onto mechanism. Instead of competing with the other existing controlled free radical polymerization technologies, the AMS copolymer method, with competitive cost and no small molecular residues, offers an alternative tool for polymer chemists to develop block copolymers on an industrial scale for some applications, such as dispersant and compatibilizer.
    Acta Chimica Sinica -Chinese Edition- 02/2013; 71(2):151. DOI:10.6023/A12100846 · 1.43 Impact Factor
  • Shengliu Wang · Kai Yue · Lianying Liu · Wantai Yang ·
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    ABSTRACT: When dispersion polymerization of styrene (St) had run for 3h, after particle rapidly growing stage, 4,4'-dimethacryloyloxybenzophenone (DMABP) cross-linker was added to reaction system and photoreactive, core(PSt)-shell(Poly(St-co-DMABP)) particles with rich benzophenone (BP) groups on surface were prepared. Polymerization of DMABP could occurred mainly on the preformed core of PSt because its diffusion could be impeded by (1) compactness of particles formed at the moment of cross-linker addition (more than 80% of monomer had been consumed, particles were no longer fully swollen by monomer), (2) reduced polarity of continuous phase, and (3) immediate occurrence of cross-linking. Subsequently, photoreactive, cross-linked hollow particles were yielded by removal of uncross-linked core in THF. SEM and TEM observation demonstrated the formation of core-shell structure and improvement of shell thickness when DMABP content increased. UV-vis spectra analysis on polymer dissolved in THF indicated that there is no polymer of DMABP in core. FTIR spectra analysis and XPS measurement further revealed that BP component on particle surface was enriched when amount of DMABP increased. Finally, an anti-fouling polymer (poly (ethylene glycol), PEG) and protein of mouse IgG was immobilized on particle surface under UV irradiation, as confirmed by FTIR spectra analysis, SEM observation and TMB color reaction.
    Journal of Colloid and Interface Science 08/2012; 389(1):126-33. DOI:10.1016/j.jcis.2012.08.047 · 3.37 Impact Factor
  • Xiaofang Yang · Lianying Liu · Wantai Yang ·
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    ABSTRACT: By exploringly introducing a bicationic viologen, N-hexyl-N'-(4-vinylbenzyl)-4,4′-bipyridinium bromide chloride (HVV) to dispersion polymerization of styrene (St) in a mixture of methanol and water, we achieved the following results: (1) monodisperse, core-shell microspheres with antibacterial surface were prepared by a simple one-step procedure, (2) diameter, core radii and shell thickness of resultant particles could be controlled by concentrations of HVV, monomer and initiator, and composition of media, (3) HVV could act not only as a monomer as that in previous modifications, but also as an efficient, novel stabilizer, and its copolymerization with St at interfacial layer and coagglutination of (co-)oligomers on core surface due to its moderate reactivity and hydrophilicity were conceived to be main reasons for formation of core-shell structures. Effects of HVV on polymerization behavior of St, evolution of core-shell structure, and morphology, size of particles were investigated. Moreover, antibacterial activity of resulted microspheres against Staphylococcus aureus was assayed.
    Polymer 05/2012; 53(11):2190–2196. DOI:10.1016/j.polymer.2012.03.038 · 3.56 Impact Factor
  • Le Cao · Lianying Liu · Wantai Yang ·
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    ABSTRACT: Monodisperse core-shell microspheres of polystyrene (PSt) contained photo-iniferter moieties were prepared first by a two-stage dispersion polymerization in which /3-methaeryloxylethyl 2-N,N-diethyldithiocarbamylacetate (MAEDCA) was charged into a reaction system after nucleation. Subsequently, raspberry-like PSt/poly acrylamide (PAM) particles were achieved by an ultraviolet light-induced surface grafting polymerization of acrylamide (AM) using the as-prepared photosensitive PSt particle as an initiator, and in a medium of methanol which is not a good solvent for the grafted chain of PAM. The morphology and core-shell structure of as-produced particles were revealed by scanning electron microscope (SEM) and transmission electron microscope (TEM) observation. Fourier transform infrared spectroscopy (FTIR), ultraviolet and visible absorption spectroscopy (UV-Vis), nuclear magnetic resonance ('H-NMR) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated that the degree of incorporated photo-iniferter moieties on particle surface improved with the increase of MAEDCA added in system. In addition, it is advantageous to achieve narrowly distributed microspheres when a mixture of MAEDCA, styrene (St),2,2'-azodiisobutyronitrile (AIBN).methanol (MeOH) and H20 were introduced into the system in the second stage of dispersion polymerization. The surface of PSt particles grafted with PAM became hydrophilic, and on which Ag nano-particles were attached readily.
    Acta Polymerica Sinica 02/2012; 012(2):117-124. DOI:10.3724/SP.J.1105.2012.11098 · 0.64 Impact Factor
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    Yuhong Ma · Lianying Liu · Wantai Yang ·
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    ABSTRACT: This feature article covers the fundamental chemistry and applications of photo-induced living surface grafting polymerization. The mechanism of activation of inert alkyl C–H bonds of polymer substrates, the structures of the active free radical and reversible dormant species, the modes of the grafting chain growth (including linear, branched and cross-linked variants), and the role of spatial effect are discussed. Two technologies, i.e., 1-step and 2-step processes, their features and applications in fabricating polymer brushes with precisely controlled patterns, desired functions, branched and block grafting chains on planar substrates, and polymer lamination are presented. The fabrication of 3-dimensional covalently bonded polymer particles, such as nano-sized polymer particle monolayers (with uniform and bimodal distributions), discrete solid and hollow polymer particles of micrometer size, and multilayer polymer particles on polymeric substrates are also introduced. In the last part, the application of photo-induced living surface grafting polymerization in non-planar surface modifications, such as the preparation of core–shell polymer particles, Janus particles and cross-linked hydrogels with hairy polymer chains is summarized.
    Polymer 09/2011; 52(19):4159–4173. DOI:10.1016/j.polymer.2011.07.027 · 3.56 Impact Factor
  • Yaming Zhang · Lianying Liu · Mingwei Ren · Changwen Zhao · Wantai Yang ·
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    ABSTRACT: As a microreactor, hollow microspheres could he used to load magnetic nanoparticles. Asymmetric hollow polymeric microspheres with micropores of 14. 9 nm, alkyl bromine groups on exterior wall and carboxyl groups on interior wall were produced through three steps; (a) synthesis of the core-shell microparticles with copolymer of maleic anhydride (MAn) and divinyl benzene (DVB) as the shell, and copolymer of maleic anhydride (MAn) and vinylacetate (VAc) as the core; (b) surface bromizing of the core-shell microparticles by reaction with dibromoethane; (c) etching of the cores with acetone, and followed by the hydrolyzing of the anhydride groups on interior wall. Fe 3O 4 magnetic nanoparticles were loaded into the cavity of prepared hollow polymeric microspheres by two steps; first, Fe 2+ and Fe 3+ were infiltrated into the hollow microspheres and selective adsorbed on the interior wall under the effect of carboxyl groups; secondly, in appropriate condition, coprecipitation were carried out to obtain Fe 3O 4 magnetic nanoparticles. In addition, influences of parameters relating to the above mentioned reaction, such as the mole ratio of Fe 2+ and Fe 3+, reaction temperature and reaction time, on the saturation magnetization of the magnetic microspheres were investigated. The results show that, the optimum reaction conditions to the balance of loading selectivity and value of saturation magnetization were as follow; molar ratio of Fe 2+ and Fe 3+ was 2/3, reaction temperature was 80°C and reaction time was 1.5 h, for obtained the best value of saturation magnetization 12.34 emu/g.
    Acta Polymerica Sinica 05/2011; 011(5):502-508. DOI:10.3724/SP.J.1105.2011.10115 · 0.64 Impact Factor
  • Jieyu Zhang · Lianying Liu · Wantai Yang ·
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    ABSTRACT: Amino-functionalized polystyrene nanoparticles were prepared by a facile approach. First, an amino functionalized monomer N-(3-aminopropyl)-p- vinylbenzylimine (CVPD) was synthesized by the displacement reaction of 4-vinylbenzy chloride and 1,3-propane diamine between dichloromethane. Then the nano-latex of styrene and N-(3-aminopropyl)-p-vinylbenzylimine copolymer were synthesized by UV-induced emulsion polymerization with water-soluble 4-(2-hydroxyethoxy) phenyl-(2-hydroxy-2-propyl) ketone (Irgacure 2959) as the photo-initiator and cetyltrimethylammonium bromides (CTAB) as the surfactant. The surfactant amount is only 0.1 wt% ∼0.8 wt% of the total system, much lower than that of mieoemulsion polymerization system which is generally used to synthesize nanoparticles. The diameter and diameter distribution of the P(St-co-CVPD) nanoparticles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The amino groups of the copolymer were evident from Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR), and the quantity of the amino groups was calculated by ninhydrin reaction. The effects of St/CVPD ratios, initiator concentrations, surfactant concentrations and UV light intensity on the polymerization system were investigated, respectively. The results show that amino-functionalized polystyrene particles with diameters of 30 ∼ 600 nm, and amino group contents of 1.2 × 10-5 ∼ 1.6 ×10 -4 mol/g could be conveniently prepared by this method. The polymerization rate of this emulsion polymerization system is fast, and the monomer conversion can reach 80% within 60 min. The amino group content can be controlled by varying St/CVPD ratios. The particle size can be tuned by changing St/CVPD ratios, initiator concentrations, surfactant concentrations and UV light intensity.
    Acta Polymerica Sinica 12/2010; 00(12):1451-1457. DOI:10.3724/SP.J.1105.2010.09484 · 0.64 Impact Factor
  • Fen Zhang · Yuhong Ma · Lianying Liu · Wantai Yang ·
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    ABSTRACT: This article presents observations of three polymerization modes of a self-developed cation-charge-stabilized styrene/water/methanol dispersion polymerization system: (1) a water/methanol (20/80) system, corresponding to a typical dispersion polymerization mode where the particle nucleation occurred in the solution phase and growth in the particle phase; (2) a pure CH(3)OH system, including a first nucleation in the solution phase with growth by absorption of the small particles and polymers formed in this phase, and a secondary nucleation with growth in the particle phase, when high molecular weight copolymers appeared in the solution phase; and (3) a water/methanol (5/95) system, similar to the conventional dispersion polymerization mode during the first 90 min, with subsequent epitaxial growth. Interestingly, the metastable state of the nucleation stage, including minuscule 6-nm particles, their aggregates, and the aggregating process, was first observed experimentally. By quantitatively following the relationship of the deposited molecular weight and the nucleation/growth process in the three systems, it was proposed that the molecular weight of the deposited polymer had to reach a specific high value before they could absorb or capture monomer to form smooth/spherical nuclei or particles.
    The Journal of Physical Chemistry B 09/2010; 114(34):10970-8. DOI:10.1021/jp102936n · 3.30 Impact Factor
  • Shengjie Lv · Lianying Liu · Wantai Yang ·
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    ABSTRACT: There exists a great number of publications concerning the synthesis of core-shell and/or hairy particles by means of controlled/living polymerization. Nevertheless, how to fabricate ultrafine nanosized hairy particles, especially polymeric soft hairy particles, remains a significant challenge. This paper presents a simple self-developed approach consisting of a two-step photoinduced polymerization of cross-linked Polyacrylamide (CLPAM) soft hydrogel nanoparticles (5-10 nm in diameter) grafted with poly(N-isopropylacrylamide) (PNIPAm) chains. The architecture of such ultrafine soft waterswollen [email protected] /* */ core/shell nanoparticles (20-35 nm in diameter) demonstrated very specific temperature sensitive behaviors. During heating a fast association process was observed, at approximately 33-34 °C and. the singular hairy particles with 34 nm diameters clustered into aggregates that were ∼120 nm in diameter. Raising the temperature further, however, led to a decrease in size to about 100 nm at 45 °C. This behavior was attributed to the formation of hydrophobic shell layers accompanying the shrinkage of PNIPAm chains with chain polar transformations. With the contraction pressure produced by further shrinkage of the hydrophobic shell layers, the soft fully swollen PAM cores expelled water and diminished in size, During the cooling process, these contracted cores that were trapped in the aggregates gave rise to an early dissociation. The hydrophilic hairy CLPAM@PNIPAm particles are believed to be potentially useful as carriers to specific target regions, e.g., cells for controlled drug delivery and other smart biomaterial applications.
    Langmuir 10/2009; 26(3):2076-82. DOI:10.1021/la9025766 · 4.46 Impact Factor
  • Hui Meng · Lianying Liu · Wantai Yang ·
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    ABSTRACT: In virtue of the reversible coupling and cleaving mechanism involved isopropylthioxanthone (ITX), a precursor of poly(methyl methacrylate) ended with ITX residues (PMMA-ITXH) was firstly synthesized through the photopolymerization of methyl methacrylate (MMA) initiated by a binary system of ITX and ethyl-p-dimethyl amino benzoate (EDAB), and secondly, applying this precursor as a macroinitiator, block copolymer of poly(methyl methacrylate) and polystyrene (PMMA-b-PSt) was produced through a thermal activated radical polymerization of styrene (St) at a temperature above 80°C. The content of incorporation of the reduced ITX groups in the precursor was estimated by UV-vis spectrum analysis and the results indicated that it was greatly influenced by the ITX concentration in system. The presence of EDAB could promote the polymerization and result in high monomer conversions and low molecular weight of polymers with wide distributions, but had no evident effect on the incorporation of reduced ITX moieties in polymer. Furthermore, more monomer supplied in system was advantageous for the production of high molecular weight of polymers and provided apparently low content of reduced ITX residues in polymer. Using a selected precursor of PMMA-ITXH with a moderate level of reduced ITX residues, molecular weight and its distribution, the bulk polymerization of St was initiated. FTIR spectrum analysis and GPC measurement confirmed the formation of block copolymer of PMMA-b-PSt.
    Journal of Macromolecular Science Part A 07/2009; 46(9):921-927. DOI:10.1080/10601320903078404 · 0.81 Impact Factor
  • Lianying Liu · Mingwei Ren · Wantai Yang ·
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    ABSTRACT: Polymeric Janus particles are obtained by UV-induced selective surface grafting polymerizations and coupling reactions, in virtue of the light-absorption of photoreactive materials such as the immobilized photoinitiator and spread photoinitiator solution on the surfaces exposed to UV light and the sheltering of densely arrayed immovable particles from light. Varying the monomers or macromolecules applied in photografting polymerization or coupling reaction, and choosing diverse polymeric particles of various size, bicolor and amphiphilic Janus particles could be successfully achieved. Observations by fluorescence microscope, scanning electron microscope ,and transmission electron microscope confirmed the asymmetrical morphology of the resultant Janus particles.
    Langmuir 07/2009; 25(18):11048-53. DOI:10.1021/la901364a · 4.46 Impact Factor
  • Jianping Deng · Lifu Wang · Lianying Liu · Wantai Yang ·
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    ABSTRACT: As one of the major techniques developed to achieve surface modification of polymeric materials, UV-induced surface graft polymerization has been widely applied as a simple, useful and versatile approach to improve the surface properties of polymers. This review surveys the recent advances in UV light induced surface graft polymerizations, predominantly focusing on: (1) various initiating methods, controlled/living grafting, self-initiated grafting (grafting without the addition of photoinitiators), graft polymerizations with monomer pairs able to form charge transfer (CT) complexes, grafting in liquid, vapor and bulk phase, and the substrates used for grafting; (2) the topography of grafted surface layers, including granular structure, crosslinked structure, and well-defined structure; and (3) the application of techniques to prepare functionalized polymer surfaces with designed performances, e.g., to obtain polymer materials suitable for biomedical applications, membranes or microfluidics.
    Progress in Polymer Science 02/2009; 34(2):156-193. DOI:10.1016/j.progpolymsci.2008.06.002 · 26.93 Impact Factor
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    Qin Wang · Lianying Liu · Wantai Yang ·
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    ABSTRACT: The grafting polymerization of styrene on the surface of commercial available vulcanized acrylonitrile butadiene rubber (NBR) latex was initiated by the heat decomposing cleavage of dormant groups of semipinacol (SP) immobilized firstly under UV irradiation. Extremely high grafting efficiency in the range from about 90% to nearly 100% could be achieved. Certain factors affinitive to the grafting polymerization, such as the concentration of monomer, the UV irradiation time taking on the immobilization of SP groups, and concentration of NBR latex containing SP groups, were investigated. It was noted that there was the highest conversion when the weight ratio of NBR and St was 4:6; the grafting polymerization had a constant grafting efficiency that was almost not affected by polymerization time and the ratio of NBR-SP/St. Furthermore, the morphologies of the thermal compression molded composites of NBR/NBR-g-PSt were observed by TEM and the thermal properties as well as tensile behaviors were examined. Obviously rubber-plastic transition could be displayed with the increasing of grafting yield. When the grafting yield was controlled at about 50%, the strength of modified rubbers increased significantly without losing its elongation.
    Polymer Journal 01/2008; 40(3):192-197. DOI:10.1295/polymj.PJ2007114 · 1.65 Impact Factor