改性聚偏氟乙烯接枝共混聚苯乙烯磺酸膜的制备与性能

将苯乙烯添加到溶有原硅酸钠改性的聚偏氟乙烯(PVDF)N-甲基吡咯烷酮溶液中, 以过氧化苯甲酰(BPO)作引发剂, 苯乙烯直接接枝到原硅酸钠改性的PVDF链上, 成膜后磺化制备了聚偏氟乙烯接枝苯乙烯(PVDF-g-PSSA)膜. 采用傅立叶变换红外光谱(FT-IR)、扫描电镜(SEM)、能量扩散X射线(EDX)和多功能材料实验机表征了膜的结构、形貌及硫和硅的分布、机械强度、溶胀度, 使用阻抗分析和气相色谱仪研究了苯乙烯含量(w)对PVDF-g-PSSA膜的质子导电性能和阻醇性能的影响. 结果表明, 苯乙烯加入后, 原硅酸钠改性的PVDF与苯乙烯进行接枝共聚反应, 苯乙烯磺化反应不只是在膜表面进行, 同时渗入到膜中进行, 机械性能得到了改善. 质子电导率(σ)随苯乙烯质量分数的提高而升高. Na4SiO4为8%和苯乙烯为20%的PVDF-g-PSSA膜, 在25 ℃时溶胀度仅为20.4%, 甲醇透过系数在10-7 cm2·s-1数量级上, 比Nafion115膜的低一个数量级. 该膜具有较高的选择性, 在直接甲醇燃料电池中具有良好的应用前景.     

碱处理PVDF膜对制备高电导率质子交换膜的作用

燃料电池是一种高能量密度、低污染的新型能源. 质子交换膜是燃料电池的核心组件之一. 在对聚偏氟乙烯(PVDF)膜进行了碱处理改性的基础上制备了高电导率的聚偏氟乙烯接枝聚苯乙烯磺酸(PVDF-g-PSSA)质子交换膜, 对碱处理后的PVDF膜进行了傅立叶变换红外光谱(FTIR)、傅立叶变换拉曼光谱(FT-Raman)及电子自旋共振(ESR)分析. 振动光谱显示在处理后的膜中存在共轭碳碳双键. 首次用ESR检测到碱处理后的PVDF膜中形成了自由基, 其浓度在10¹⁶ spin/g. 研究表明碱处理引起的膜结构变化有利于接枝反应的进行, 对提高所合成的质子交换膜的电导率有重要作用, 电导率提高一个数量级, 至6.40×10^－2 S/cm.     

PSSA pore-filled PVDF membranes by simultaneous electron beam irradiation: Preparation and transport characteristics of protons and methanol

Polystyrene sulfonic acid (PSSA) pore-filled poly(vinylidene fluoride) (PVDF) membranes have been prepared using simultaneous electron irradiation method. Porous PVDF films were grafted by pre-swelling in styrene solution and subsequent irradiation with an electron beam (EB) under nitrogen atmosphere and at ambient temperature. The grafted films i.e. polystyrene (PS) pore-filled PVDF were subsequently sulfonated with a diluted mixture of chlorosufonic acid. The effects of the reaction parameters on the content of PS grafted in the pores of PVDF films were investigated. The chemical and morphological properties of the membranes in comparison with their un-grafted and grafted counterparts were studied by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The transport properties of these membranes such as ionic conductivity and methanol permeability were evaluated and correlated with the content of PS grafted in the pores of the PVDF films. The PSSA pore-filled PVDF membranes with PS content in the pores of 40% and above showed superior performance characteristics compared to Nafion 117 membrane and therefore can be potential alternatives to improve the performance of direct methanol fuel cell (DMFC).     

Synthesis and properties of sulfonated and crosslinked poly[(vinylidene fluoride)-graft-styrene] membranes

Crosslinked proton exchange membranes were prepared by electron beam grafting of styrene with divinylbenzene, DVB, or bis(vinyl phenyl)ethane, BVPE, on to poly(vinylidene fluoride), PVDF, followed by sulfonation. The area and thickness increase, crystallinity and mechanical properties of the membranes were investigated. All these properties were influenced by the crosslinker structure and its concentration. The crosslinkers increase the final degree of grafting. For noncrosslinked membranes it was about 80% and with 10% of BVPE crosslinker about 180% after 8 hr. The area increase with grafting is very similar for the noncrosslinked membranes and the differently crosslinked membranes, but the crosslinkers reduce swelling for sulfonated membranes swelled in boiling water. DVB reduces swelling more than BVPE. With grafting, the crystallinity of the PVDF phase decreases; with 10% BVPE the decrease is smallest and with 10% DVB largest. The mechanical properties of the sulfonated swelled membranes decrease with the degree of grafting, for a 10% DVB crosslinked membrane the strength decreases to zero at degrees of grafting higher than 75%. © 1998 John Wiley & Sons, Ltd.     

New polymer electrolyte membranes for low temperature fuel cells

Partially fluorinated proton exchange materials were synthesised by pre-irradiation grafting of styrene into poly(vinylidene fluoride) films with subsequent sulfonation. The grafted and sulfonated membranes, PVDF-g-PSSA membranes, have been studied with respect to water uptake, ion and water clustering, ion conductivity and water diffusion coefficients. Water associates with the membranes in three different ways: bound non-freezable water, freezable bound water and freezable free water. The proton conductivity of the membrane is strongly dependent on the hydration, it decreases more rapidly than the water self diffusion with decreasing water content. Ion clusters with a Bragg distance of 25 Å form the conducting channels in the membranes.     

Phase separation and crystallinity in proton conducting membranes of styrene grafted and sulfonated poly(vinylidene fluoride)

A series of proton exchange membranes have been prepared by the preirradiation grafting method. Styrene was grafted onto a matrix of poly(vinylidene fluoride) (PVDF) after electron beam irradiation. Part of the samples was crosslinked with divinylbenzene (DVB) or bis(vinylphenyl)ethane (BVPE). Subsequent sulfonation gave membranes grafted with poly(styrene sulfonic acid) and marked PVDF‐g‐PSSA. It was found that the intrinsic crystallinity of the matrix decreased in both the grafting and the sulfonation reaction in all the membranes. The graft penetration and the ion conductivity are influenced strongly by the crosslinker. The ion conductivity is considerably lower in crosslinked membranes than in noncrosslinked ones. Generally, the mechanical strength decreases with crosslinking. The membranes show a regular phase separated structure in which the sulfonated grafts are incorporated in the amorphous parts of the matrix polymer. The phase separated domains are small, of the order of magnitude of 100–250 nm. These were resolved on transmission electron micrographs and on atomic force images but could not be resolved with microprobe Raman spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1741–1753, 1999     

质子交换膜对钒氧化还原液流电池性能的影响

采用溶液接枝聚合法制备了一种新型的质子交换膜PVDF-g-PSSA, 测定了PVDF-g-PSSA膜、Nafion 117 膜和PE01均相膜的离子交换能力和电导率, 并分别研究了以这3种膜为隔膜的钒电池的电化学性能. 实验结果表明, PVDF-g-PSSA膜具有优良的质子电导率和离子交换能力, 室温下其离子交换能力和质子电导率分别为1.13 mmol/g和3.22×10-2 S/cm, 在不同的充放电电流密度下, 以PVDF-g-PSSA膜为隔膜的钒电池的库仑效率和能量效率明显高于Nafion 117膜和PE01均相膜为隔膜的钒电池; PVDF-g-PSSA膜阻钒离子的渗透性能与PE01均相膜基本一致, 都明显优于Nafion 117膜的阻钒离子渗透能力.     

ASAXS study of styrene‐grafted sulfonated poly(vinylidene fluoride) membranes

Small‐angle and wide‐angle X‐ray scattering and anomalous small‐angle X‐ray scattering were used to investigate proton‐conducting membranes prepared by radiation‐induced styrene grafting and sulfonation of commercial poly(vinylidene fluoride) (PVDF‐g‐PS) films. The membranes retain the lamellar and highly oriented structure of the original PVDF films even through excessive grafting and sulfonation. The sulfonate groups aggregate in the central part of the amorphous layers, where they form a weakly ordered structure that does not show any preferred orientation. This structure is suggested to be lamellar with alternate metal‐sulfonated hydrate and PVDF‐g‐PS layers. The lamellar period is 15.1 Å. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1734–1748, 2000     

Thermal properties and structure of electrospun blends of PVDF with a fluorinated copolymer

We report the structure and thermal properties of blends comprising poly(vinylidene fluoride) (PVDF) and a random fluorinated copolymer (FCP) of poly(methyl methacrylate)‐random‐1H,1H,2H,2H‐perfluorodecyl methacrylate, promising membrane materials for oil–water separation. The roles of processing method and copolymer content on structure and properties were studied for fibrous membranes and films with varying compositions. Bead‐free, nonwoven fibrous membranes were obtained by electrospinning. Fiber diameters ranged from 0.4 to 1.9 μm, and thinner fibers were obtained for PVDF content >80%. As copolymer content increased, degree of crystallinity and onset of degradation for each blend decreased. Processing conditions have a greater impact on the crystallographic phase of PVDF than copolymer content. Fibers have polar beta phase; solution‐cast films contain gamma and beta phase; and melt crystallized films form alpha phase. Kwei's model was used to model the glass transition temperatures of the blends. Addition of FCP increases hydrophobicity of the electrospun membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 312–322     

Influences of permeation of vanadium ions through PVDF-g-PSSA membranes on performances of vanadium redox flow batteries

The preparation and physical characterization of a poly(vinylidene fluoride)-graft-poly(styrene sulfonic acid) (PVDF-g-PSSA) membrane prepared by a solution-grafting method were described. These membranes exhibited high conductivity with a value 3.22 x 10(-2) S/cm at 30 degrees C. ICP studies revealed that the PVDF-g-PSSA membrane showed dramatically lower vanadium ion permeability compared to Nafion 117. Trivalent vanadium ions had the highest permeability through all these membranes in contrast to pentavalent vanadium ions with the lowest. The VRB with the low-cost PVDF-g-PSSA membrane exhibited a higher performance than that with Nafion 117 under the same operating conditions, and its energy efficiency reached 75.8% at 30 mA/cm(2). The performance of VRB with the PVDF-g-PSSA membrane can be maintained after more than 200 cycles at a current density of 60 mA/cm(2).     

TEMPO addition into pre-irradiated fluoropolymers and living-radical graft polymerization of styrene for preparation of polymer electrolyte membranes

We prepared proton exchange membranes (PEMs) by 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-mediated living-radical graft polymerization (LRGP) of styrene into fluoropolymer films and subsequent sulfonation. Poly(vinylidene fluoride) (PVDF) and poly(ethylene-co-tetrafluoroethylene) (ETFE) films were first irradiated and then treated with TEMPO solutions in various solvents. TEMPO addition was confirmed by the test of styrene grafting into TEMPO-treated films at 60 °C, at which the LRGP never proceeds. This test enabled us to differentiate the LRGP from the conventional graft polymerization. In order to gain a deep insight about TEMPO-addition reaction, the TEMPO-penetration behavior into the base polymer films was examined by a permeation experiment and computer simulation. Xylene and dioxane were appropriate solvents for the complete introduction of TEMPO into PVDF and ETFE films, respectively. Then, the LRGP of styrene was performed based on the fully TEMPO-capped films at 125 °C with various solvents. By using an alcoholic solvent, the degree of grafting was enhanced and it reached a maximum of 38%. This grafted film was sulfonated to prepare a PEM showing an ion exchange capacity of 2.2 meq/g and proton conductivity of 1.6×10^?1 S/cm.     

Increase in crystallinity in poly(vinylidene fluoride) by electron beam radiation

We examine the influence of high-energy radiation and subsequent aging and orientation on the degree of crystallinity of poly(vinylidene fluoride) (PVDF) films. In particular, PVDF films were exposed to electron beam radiation (doses up to 50 Mrad) and aged at room temperature for varying lengths of time followed by uniaxial orientation. The degree of crystallinity of these films was found to increase significantly with increasing radiation dose. In addition, a further substantial increase in the degree of crystallinity was observed upon subsequent aging of irradiated films at room temperature. Upon orientation, in addition to a further rise in the degree of crystallinity, the crystallites were observed to undergo the α form → β form transformation, the latter phase being the polar phase effective for piezo-electric/pyroelectric activity.     

Effect of the initial matrix material on the structure of radiation‐grafted ion‐exchange membranes: Wide‐angle and small‐angle X‐ray scattering studies

Seven different fluoropolymer films were used as matrix materials for radiation‐grafted ion‐exchange membranes. The crystallinity and preferred orientation of these membranes were studied with wide‐angle X‐ray scattering, and the lamellar structure of the membranes was examined with small‐angle X‐ray scattering. The crystallinity of poly(vinylidene fluoride) (PVDF)‐based matrix materials varied between 57 and 40%, and the crystallinity of the sulfonated samples varied between 34 and 23%. The lamellar periods of PVDF‐based matrix materials were about 115 Å, and the lamellar periods of poly(ethylene‐alt‐tetrafluoroethylene) and poly(tetrafluoroethylene‐co‐hexafluoropropylene) were 250 and 212 Å, respectively. When the samples were grafted, the lamellar periods increased. Correlation function analysis showed very clearly that the long‐range order decreased because of grafting and sulfonation processes. For those samples that showed good proton conductivity, the lamellar period also increased because of sulfonation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1539–1555, 2002     

Electron-beam graft-modified membranes with externally controlled flux

Pre-irradiation grafting as a means to modify commerical poly(vinylidene fluoride) (PVDF) membranes has been studied. The membranes prepared were weak cation-exchange membranes (acrylic acid functionality), anion-exchange membranes (trimethyl ammonium functionality) and temperature-sensitive membranes (N-isopropyl amide functionality). Different graft loads were obtained by varying reaction time, radiation dose and in the case of acrylic acid the graft solution composition. The trimethyl ammonium chloride functionality was obtained by grafting vinyl benzyl chloride onto a PVDF membrane and aminating the benzyl chloride groups in a 45% trimethyl amine–water solution. For a membrane grafted with 9 wt% acrylic acid the flux increased approximately 70 times when the pH was decreased from 6 to 2. For a membrane with 5 wt% trimethyl ammonium functionality the flux increased both when pH was decreased below 3 and increased above 11. For a membrane grafted with 18 wt% N-isopropyl acrylamide a sharp increase of flux was observed when the temperature was raised above 32°C.     

Preparation and application of polystyrene‐grafted ZnO nanoparticles

The precursor of ZnO was prepared by precipitation and ZnO nanoparticles were obtained by calcination afterwards. Poly(styrene) (PSt) was grafted onto the ZnO nanoparticles in a non‐aqueous suspension to reduce the aggregation among nanoparticles and to improve the compatibility between nanoparticles and the organic matter. The obtained samples were characterized by X‐ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT‐IR), zeta potential measurement, lipophilic degree (LD) test, photocatalytic experiments, sedimentation test, and contact angle measurement. The LD of composite particles after a high‐temperature treatment was stable. The photoluminescence of PSt‐grafted ZnO nanoparticles was observed by naked eyes and was recorded using a digital camera. The ZnO nanoparticles were used to reinforce poly(vinylidene fluoride) (PVDF) films and the mechanical and electric properties of the films were also measured. Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation and dielectric properties of composites based on PVDF and PVDF-grafted graphene obtained from electrospinning-hot pressing method

In this work, graphene was modified by the grafting of poly(vinylidene fluoride) (PVDF) using Friedel-Crafts reaction to form PVDF-grafted graphene (PGG) filler, which was confirmed by transmission electron microscope, Fourier transform infrared, Raman spectroscopy, wide angle X-ray diffraction, and thermogravimetric analysis. The solution containing as-prepared PVDF-grafted graphene and PVDF was electrospun to form fibrous membranes, which was subjected to hot pressing in the laminating mode to prepare solid PGG/PVDF composite films. The structures of electrospun fibrous membrane and solid PGG/PVDF composite film were investigated by scanning electron microscope. Furthermore, it could be found that the dielectric constants of PGG/PVDF composites exhibiting relatively low dielectric loss factors were significantly higher than that of pure PVDF.     

表面引发的原子转移自由基聚合法在聚偏二氟乙烯表面制备可控的聚甲基丙烯酸甲酯刷

采用表面引发的原子转移自由基聚合法(ATRP)在聚偏二氟乙烯(PVDF)表面制备结构可控的聚甲基丙烯酸甲酯刷。通过碱处理和紫外光照溴代的方法,将ATRP引入到PVDF表面; 然后采用ATRP法将甲基丙烯酸甲酯接枝到溴代的PVDF表面。采用傅里叶变换红外光谱和X-射线光电子能谱对改性前后PVDF表面的结构进行了表征。结果表明甲基丙烯酸甲酯成功地接枝到了PVDF表面。     

Biofouling resistance of ultrafiltration membranes controlled by surface self-assembled coating with PEGylated copolymers

Block and random PEGylated copolymers of poly(ethylene glycol) methacrylate (PEGMA) and polystyrene (PS) were synthesized with a controlled polydispersity using an atom transfer radical polymerization method and varying molar mass ratios of PS/PEGMA. Two types of PEGylated copolymers were self-assembly coated onto the surface of poly(vinylidene fluoride) (PVDF) ultrafiltration membranes for enhancing biofouling resistance. It was found that the adsorption capacities of random copolymers on PVDF membranes were all higher than those of block copolymers. However, the specific and overall protein resistance of bovine serum albumin (BSA) on PVDF membranes coated with block copolymers was much higher than that with random copolymers. The increase in styrene content in copolymer increased the amount of polymer coating on the membrane, and the increase in PEGMA content enhanced the protein resistance of membranes. The optimum PS/PEGMA ratio was found to be close to 2 for the best resistance of protein adsorption and bacterial adhesion on the PEGylated diblock copolymer-coated membranes. The PVDF membrane coated with such a copolymer owned excellent biofouling resistance to BSA, humic acid, negatively surface charged bacteria E. coli, and positively surface charged bacteria S. maltophilia.     

Hemocompatibility of poly(vinylidene fluoride) membrane grafted with network-like and brush-like antifouling layer controlled via plasma-induced surface PEGylation

In this work, the hemocompatibility of PEGylated poly(vinylidene fluoride) (PVDF) microporous membranes with varying grafting coverage and structures via plasma-induced surface PEGylation was studied. Network-like and brush-like PEGylated layers on PVDF membrane surfaces were achieved by low-pressure and atmospheric plasma treatment. The chemical composition, physical morphology, grafting structure, surface hydrophilicity, and hydration capability of prepared membranes were determined to illustrate the correlations between grafting qualities and hemocompatibility of PEGylated PVDF membranes in contact with human blood. Plasma protein adsorption onto different PEGylated PVDF membranes from single-protein solutions and the complex medium of 100% human plasma were measured by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. Hemocompatibility of the PEGylated membranes was evaluated by the antifouling property of platelet adhesion observed by scanning electron microscopy (SEM) and the anticoagulant activity of the blood coagulant determined by testing plasma-clotting time. The control of grafting structures of PEGylated layers highly regulates the PVDF membrane to resist the adsorption of plasma proteins, the adhesion of platelets, and the coagulation of human plasma. It was found that PVDF membranes grafted with brush-like PEGylated layers presented higher hydration capability with binding water molecules than with network-like PEGylated layers to improve the hemocompatible character of plasma protein and blood platelet resistance in human blood. This work suggests that the hemocompatible nature of grafted PEGylated polymers by controlling grafting structures gives them great potential in the molecular design of antithrombogenic membranes for use in human blood.     

Single-step synthesis of proton conducting poly(vinylidene fluoride) (PVDF) graft copolymer electrolytes

The single-step synthesis of proton conducting poly(vinylidene fluoride) (PVDF) graft copolymer electrolytes is demonstrated. The graft copolymers of PVDF backbone with poly(sulfopropyl methacrylate) (PVDF-g-PSPMA) and poly(styrene sulfonic acid) (PVDF-g-PSSA) were synthesized using PVDF as a macroinitiator for atom transfer radical polymerization (ATRP). ¹H NMR and FT-IR spectroscopy show that the “grafting from” method using ATRP was successful and the maximum grafting degrees were 35 and 25 wt% for PVDF-g-PSPMA and PVDF-g-PSSA, respectively. The IEC values were 0.63 and 0.45 meq/g, the water uptakes were 46.8 and 33.4 wt% and the proton conductivities were 0.015 and 0.007 S/cm at room temperature, for PVDF-g-PSPMA and PVDF-g-PSSA, respectively. Both membranes exhibited excellent thermal stability up to around 350 °C, verified by thermal gravimetric analysis (TGA).