最新刊期
卷 37 ， 期 5 ， 2017
- 摘要：Single chain models are the simplest molecular models for theoretical study on dilute polymer solutions. The corresponding results are useful for studying the basic dynamic properties, such as the intrinsic viscosity and self-diffusivity, and provide an important way of understanding the relationship between molecular architectures and the dilute solution properties. Earlier efforts are focused on searching for suitable constitutive equations based on principles of continuum mechanics. However, such constitutive models fail to provide a first-principle description of the polymer solutions. In order to quantitatively describe the experimental results, it is desirable to establish models or theories on a molecular level. In this review, we discuss three typical single chain models. First we begin with the first successful molecular model of polymer dynamics, Rouse model, in which each bead is connected by harmonic springs and experiences its own independent friction. There are no hydrodynamic interactions between beads. Since in polymer melts hydrodynamic interactions are screened by the other chains, the Rouse model can be used to describe the dynamics of chains in unentangled polymer melt. Then we turn to the Zimm model, which considers the motion of the polymer chains in solvent, where the hydrodynamic interaction between the segments of a chain plays a prominent role. As a result, both the polymer and the solvent molecules within the pervaded volume of the chain move together in dilute solution. Furthermore, we focus on the description of our theory for the intrinsic viscosity of polymers with arbitrary architectures, based on a partially permeable sphere model. The model introduces two phenomenological functions, the drag function and drainage function, which capture the long-range, multibody, accumulative hydrodynamic interactions at the mean-field level. Predictions from our theory are in good agreement with experimental data on all the polymer structures examined, ranging from linear, ring and stars to hyperbranched polymers as well as dendrimers. At the end of this review, we also briefly discuss the critical issues, development prospects and research directions in this field.关键词：Rouse model;Zimm model;Partially permeable sphere model;Hydrodynamic interaction;Intrinsic viscosity
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发布时间：2021-03-19
Reviews
- 摘要：Polyelectrolyte multilayer films were fabricated by layer-by-layer deposition of polyacrylic acid (PAA) and polyethyleneimine (PEI). The (PAA/PEI) films showed unique dynamic properties owning to the high mobility of the polymer molecules:the spongy microporous structure was formed through an acid treatment for 60 min; and the porous structure disappeared under a 100% relative humidity treatment, back to a solid film. Based on this (PAA/PEI) platform, lysozyme was easily loaded into the film via a wicking action in 5 s, and then easily immobilized into the film after 8 h conservation in humid atmosphere, providing therefore a novel approach to prepare antibacterial coating without any specific requirement for the characteristic of the agents. Scanning electron microscope was employed to show the dynamic transformation of film structures, from the original film with 9.5 nm of thickness to spongy sporous film with 68 nm of thickness and back to the solid film of 12 nm after the conservation process. Confocal scanning laser microscope image showed an even distribution of lysozyme in the film with lysozyme labelled by FITC. Loading quantity and the release dynamics of lysozyme were tested utilizing ultraviolet-visible spectrophotometer. Further, gram positive bacteriaS. aureus and gram negative bacteria E. coli were tested in the antibacterial assay. The result illustrated that the coating was able to kill S. aureus efficiently, and the antibacterial activity of lysozyme was not affected by such loading and releasing process. To further enhance the bactericidal effect of the coating against gram negative bacteria, lysozyme and lactoferrin, which have synergistic killing effect on gram negative bacteria, were immobilized into the film at the same time and performed a distinct higher antibacterial efficiency against E. coli in comparison with the (PEI/PAA)15-lysozyme coating, revealing the attractive potential of this film as antibacterial coatings for medical devices to prevent the hospital-associated infections.关键词：Dynamic transformation;Spongy microporous structure;Lysozyme;Layer-by-layer assembly;Antibacterial coating
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发布时间：2021-03-19 - 摘要：To develop elastic fibers with high performance, long chain poly (amide-co-ether) (LPAE) elastic fiber was prepared by melt spinning based on the long chain polyamide (LCPA) elastomer. The elastomer contained LCPA as hard segment, which was produced from bio-fermenting source and features by lower water absorption, better dimensional stability and excellent mechanical properties, and polyether as the soft segment with easy conformation change. The corresponding elasticity was effectively regulated by varying the ratio of hard/soft segments. The stretching tests results confirmed that these LPAE fibers with higher fraction of soft segment represented higher elongation and lower initial modulus, compared with the commercially used LYCRA. The cyclic tensile loading measurements revealed that the corresponding elastic recovery rate was almost equal to that of LYCRA when the strain was less than 200%. Moreover, LPAE fibers favored better thermo-stability than LYCRA, verified by higher onset degradation temperature. It also offered some advantages of LCPA, such as better wear resistance, oil or solvent resistance and absorbency to skin with the amide groups. The super elasticity of the LPAE fiber may be well originated from the dual effect that the polyamide hard segments served as the physical crosslinking point due to their strong hydrogen bonding interaction and high crystallinity, and that the polyether soft segments largely deformed due to their better flexibility. The three dimensional network was created this way by alternative hard and soft segments in the polymer chains. At large strain, the strain-induced crystallization definitely occurred, as indicated by enhanced melting enthalpy, which was especially pronounced in the soft segments. Therefore, both the slippage of the molecular chain and newly formed crystals from strain-induced crystallization predominately contributed to the reduced elastic recovery. Based on the current results, it is expected that spandex can be partially replaced with the LPAE fiber in practice.关键词：Long chain poly (amide-ether)(LPAE) elastomer;Elastic fiber;Spandex;Super elasticity;Mechanism
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发布时间：2021-03-19 - 摘要：Catalyzed by a phenoxycyclopentylimine ligated zirconium complex/dried methylaluminoxane (dMAO) system at 40℃ under 1 atm of ethylene pressure, linear vinyl-terminated polyethylene (PE-ene) with nearly 100% of end-functionality was produced via ethylene polymerization. With high efficiency, hydroxyl-terminated polyethylene (PE-OH) was subsequently prepared via the radical initiated thiol-ene click chemistry between the PE-ene and 2-mercaptoethanol. The PE-OH was then used to react with norbornene-5-carbonyl chloride to synthesize the norbornene-terminated polyethylene macromonomer (PE-NB) through the esterification reaction. The ring-opening metathesis copolymerization (ROMP) of PE-NB and norbornene (NB) with the different feed ratio was conducted in the presence of Grubbs Ⅱ generation catalyst to produce the polyethylene-based graft copolymers. Both random and block polynorbornene-g-polyethylene graft copolymers (PNB-g-PE) were then obtained with different feeding mode, i.e., the one-batch feeding mode and the sequential feeding mode, respectively. The structures of the graft copolymers were characterized by Fourier transform-infrared and proton nuclear magnetic resonance spectroscopy. The molecular weight and molecular weight distribution of PNB-g-PE were determined by high-temperature gel permeation chromatography; the thermal properties of PNB-g-PE were also tested by differential scanning calorimetry. The conversion of macromonomer was found to be nearly 100% in the random copolymerization of macromonomer and norbornene. The random graft copolymers were obtained with the molecular weight of 1.79×104-3.14×104 with relatively narrow molecular weight distribution (2.09-2.60). The molecular weight of the copolymers decreased gradually with the increase in the feed ratio of PE-NB. The molar fraction of PE in the random copolymers varied from 4.6% to 16.8%, depending on the feed ratio of PE-NB to NB, whereas the molar fraction of PE showed slight influence on the melting point of the PE segments. However, the conversion of macromonomer reached about 80% in the block copolymerization of PE-NB and NB. Due to the steric hindrance, the crystallinity of the graft copolymers slightly decreased in comparison with the corresponding PE precursor.关键词：Polynorbornene;Polyethylene;Graft copolymers;Random;Block
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发布时间：2021-03-19 - 摘要：The phase behavior of a ternary blend with photochemical reaction induced by a mask are investigated via the Time-Dependent Ginzburg-Landau theory. The effects of the composition ratio, the length-width ratio of the photomask, and thephotoreaction rate coefficient on the domain structure and formation are systematically investigated. Through analysis of the phase diagram, the conditions for the formation of the ordered structures, such as island-like, network-like, and lamellar structures, are obtained. When the photoreaction rate coefficientΓ is not larger than 1×10-5, the system forms a disordered structure, regardless of the strong variations in the C component concentration and the length-width ratio of the photomask. Firstly, when the length-width ratio of the photomask is fixed (L:d=6:4), with increasing the photochemical reaction rate, the disordered morphology transforms to island-like structure when ϕC < 0.35; it forms disordered structure again when 0.35 ≤ ϕC ≤ 0.4; a transition of disordered strcture-lamellar strcture-network structure occurs in the system when ϕC> 0.4. Secondly, when the photoreaction rate coefficient is fixed (Γ=1×10-3), with increasing C component concentration, the system shows a multiple morphology transition of island-like-disordered-lamellar-network when 6:4 ≤ L:d ≤ 6:1; when 6:6 ≤ L:d < 6:4, the island-like structure changes to disordered and then to network structure. Finally, when the C component concentration is fixed ( ϕC=0.45), with the decrease in the length-width ratio of the photomask, the morphology transforms from disordered to lamellar, and then to network when 1×10-5 < Γ < 5×10 -4; when 5×10-4 ≤ Γ < 1×10 -2, the lamellar structure turns to network structure; and when Γ ≥ 1×10-2, the photochemical reaction rate is so fast that the A/B blend does not undergo the phase separation, and the macro-morphology transforms from lamellar to network. In addition, to gain insight into the stability of the structures obtained, a linear stability analysis is also carried out. The results show that these ordered structures can still be stable after the removal of the mask.关键词：Self-assembly;Photochemical reaction;Polymer mixture;Mask
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发布时间：2021-03-19 - 摘要：In order to enhance the dispersion of graphene (Gra) in PVDF matrix and improve the interface properties of the composite materials, a copolymer (P[MMA-IL]) with 1-vinyl-3-ethyl imidazole bromine (IL) and methyl methacrylate (MMA) was synthesized by radical polymerization. A series of PVDF/PMMA, PVDF/PMMA/Gra, PVDF/P[MMA-IL] and PVDF/P[MMA-IL]/Gra were prepared using a solution-cast and hot pressing method. The morphological structure, crystallization and dielectric behavior were investigated by Raman spectrometer, field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), polarized optical microscopy (POM), differential scanning calorimetry (DSC) and LCR meter, respectively. Raman spectra indicated that strong π interaction between imidazole ring and carbon ring established between P[MMA-IL] and Gra, and FESEM observation showed the good dispersity of Gra in PVDF matrix due to that interaction. DSC results indicated that,Tc of PVDF was decreased by the presence of PMMA as a diluent, and that Tc and Tm of PVDF were promoted by P[MMA-IL] modified Gra because of the presence ofβ polar crystal. Gra was modified by P[MMA-IL] as a template to increase the degree of crystallinity of PVDF. XRD and FTIR-ATR results confirmed that theβ-crystal was not induced by PMMA and Gra, but by P[MMA-IL] due to the electrostatic interaction between the >CF2 of the polymer backbone and imidazolium cation, and the strong induction was brought by the template of Gra. POM photos displayed that α-crystal with loose structure were embedded into the chip space of spherulites because the presence of MMA chain segments. The electrostatic interaction and nucleating agents of IL chain segments resulted in β crystal with small size and increased the crystallization rate. Dielectric properties study showed that PMMA and modified Gra reduced the crystallinity and concentration of PVDF chain, leading to weak interface polarization and orientation polarization of PVDF. The dielectric constant is low. While P[MMA-IL] and modified Gra induced moreβ crystal, the strong interface polarization was enhanced by β crystal and ion polarization of IL chain segments improved the dielectric constant.关键词：Polyvinylidene fluoride;Methyl methacrylate;Ionic liquid;Crystallization behavior;Dielectric behavior
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发布时间：2021-03-19 - 摘要：We prepared two kinds of monodispersed polystyrene (PS) microspheres with different surface electrical properties from the polymerization of styrene in water using different initiators. The PS microspheres prepared with potassium persulfate (KPS) as the initiator (PS-a) have negative zeta potential in water, and those prepared with 2, 2'-azobis (2-methylpropionamidine) dihydrochloride (AIBA) as the initiator (PS-c) have positive zeta potential in water. Next, PS-a and PS-c microspheres were respectively used as the templates to prepare hollow SiO2 microspheres through a sol-gel process of tetraethoxysilane (TEOS) in an ethanol/ammonia medium. Based on the analysis on the products by FTIR, SEM, TEM, TGA, and N2 adsorption-desorption isotherms, it was found that the distribution of OH- in the system depended on the surface electrical property of the PS template microspheres, which would lead to different formation processes of the silica shell on the template microspheres. When the PS-a microspheres were used as the template, the OH- ions were repulsed from the negative surface of the PS-a template microspheres, due to the electrostatic repulsion interaction. Thus, the SiO2 nanoparticles with a size of several tens of nanometers were firstly formed by hydrolysis and condensation of TEOS in the medium, and then adsorbed and packed on the surface of PS-a template microspheres through the polar interaction, resulting in the formation of a raspberry-like silica shell with macropores. After the PS-a template microspheres etched by toluene, the raspberry-like hollow silica microspheres were obtained. However, when PS-c template microspheres were used as the template, the OH- ions were adsorbed on the positive surface of the template microspheres. Then, a smooth and dense silica layer was grown directly from the surface of the template microspheres through the hydrolysis and the condensation of TEOS catalyzed by the adsorbed OH- ions. After calcination at 600℃ for 8 h, hollow silica microspheres with a smooth and mesoporous silica shell were produced. This work indicates that the morphology of the hollow silica microspheres can be controlled through the surface electrical property of the template microspheres. This study may lead to more applications of hollow silica microspheres in the area of control-release materials, drug carriers, and absorbents.关键词：Hollow microspheres;Silica;Polystyrene template microspheres;Surface electrical property;Tetraethoxysilane
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发布时间：2021-03-19 - 摘要：Polymeric micelles after cross-linking can be overcome dissociation over dilution. In order to obtain cross-linked micelles, a novel pH-responsive copolymer, P (CL-ACL)-PDEAS, namely, poly (ε-caprolactone/aazidecaprolactone)-b-poly (N, N-diethylaminoethylmethacrylate)-r-poly (N-(3-sulfopropyl)-N-methacy-loxyethy-N, N-diethylammoniumbetaine) was synthesized with azide groups in the hydrophobic block. A cross-linker, 2, 2'-bi (2"-acetylene ethyl formate) amide ethyl disulfide, was also synthesized. The synthesis process of P (CL-ACL)-PDEAS included a combination of ring-open polymerization of caprolactone monomers, replacement and transformation of end functional groups, atom transfer radical of DEA monomers and sulfonation of DEA groups. The successful synthesis of the copolymer and the cross-linker were confirmed by nuclear magnetic resonance, Fourier transform infraredand elemental analysis. P (CL-ACL)-PDEAS was used to form polymer micelles by self-assembly. The cross-linked micelles were obtained through "click" chemistry by adding the cross-linker and catalyst during the process of micelle formation. Laser particle size analyzer (DLS) and fluorescence spectrophotometer were used to characterize the properties of the micelles. As a result, the sizes of the uncross-linked micelles and cross-linked micelles were 97.34 and 121.8 nm, respectively, and unimodal size distribution was observed for both types of the micelles. However, after 1000 fold dilution, the size of the cross-linked micelles and their unimodal distribution remained, while the size of the uncross-linked micelles increased greatly and the size distribution became dual. This meant that the cross-linked micelles were more stable. In addition, acid-base titration test showed that both types of the micelles were pH-sensitive. Drug loading and release experiment were carried out using DOX as drug model. The drug loading content and the drug loading efficiency were similar for both types of the micelles. Finally, drug release experiment was executed in different conditions by simulating the human body's physiological environment. The results indicated that the cross-linked micelles released less DOX than the uncross-linked micelles under normal physiological conditions, whereas in the presence of DTT, the release rate of the cross-linked micelles was significantly accelerated, due to the disulfide bond breaking. Thus, as drug delivery carrier, the cross-linked micelles were able to release drug at specific site of tumor in response to the tumor microenvironment.关键词：Cross-linked micelles;Drug delivery;Click-chemistry;Sulfobetaines
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发布时间：2021-03-19 - 摘要：With easily removed and reused chitosan (CS) as dispersant, a series of micron-sized hard or soft polymer particles were prepared via micro-suspension polymerization. The protonation degree, hydrophilic-hydrophobic property, conformation of the CS macromolecular chains in aqueous medium at different pH and their influences on the form of the CS presence at the oil water interface were studied. The dispersion and stabilization effect of the CS chains on the monomer droplets in shear homogenization and polymerization processes were explored. It was found that, the protonation degree and hydrophilic-hydrophobic property of the CS chains can be easily controlled by adjusting the pH of the aqueous medium. And the adsorption efficiency and spreading degree of the CS chains on the monomer droplet surface can be adjusted in a wide range. All of them can be used to improve the dispersion ability and stabilizing effect of the CS chains in the micro-suspension polymerization system. Especially, when the pH of CS aqueous solution is near 6.0, the protonation degree and hydrophilic-hydrophobic property of the CS chains are suitable to form a shrinkage CS chain conformation with a certain cohesive density, and an entanglement structure consisted of a few entangled CS chains. Under this state, the monomer droplets can be well dispersed and stabilized by these CS chains, and thus a series of polymer particles with smaller particle size, narrower size distribution, regular morphology and good dispersion can be easily obtained. Comparing with inorganic powder and water-soluble polymer dispersants commonly used in micro-suspension polymerization system, this CS dispersant has many advantages, such as recyclability, better dispersion stability, higher dispersion efficiency, and excellent chain conformation controllability. CS is particularly suitable to prepare micron-sized soft particles of polymers with lowTg, and is expected to replace part of the dispersants currently used in micro-suspension polymerization.关键词：Chitosan;Micro-suspension polymerization;Dispersant;Dispersion and stabilization
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发布时间：2021-03-19 - 摘要：Protein adsorption on hydroxyapatite (HA) particle surface was investigated in this study, in which sodium caseinate (SC) and whey protein isolates (WPI) were selected as the protein models with different configuration. Besides, SC was phosphorylated protein containing different protein components, while WPI was non-phosphorylated protein. The phosphorylated serine residues (Ser-P) on protein could bind calcium ions on HA particle. The adsorption of protein on calcium salts was discussed using both nano-sized (256 nm) and micron-sized (2μm and 17μm) HA particles. The physicochemical properties of HA particle surface with or without the adsorption of SC and WPI were characterized by Fourier transform infrared spectroscopy and ζ-potential measurement. The results confirmed the proteins adsorption on the surface of HA particles with the diameters of 256 nm and 2μm. Moreover, an insignificant interaction between HA particles with limited specific surface area was observed, compared with the particles with larger specific surface area. The protein components of suspension supernatants after adsorption were analyzed by SDS-PAGE. The existence of Ser-P increased the protein adsorption and a larger amount of SC was thus adsorbed on the HA surface compared to WPI (non-phosphorylated protein). The competitive adsorption onto HA surface betweenαs1-SC and β-SC was further discussed from the difference of the number and distribution of Ser-P on the peptide chain. The αs1-SC and β-SC are multi-phosphorylated with a conserved cluster sequence of 3 Ser-P followed by 2 glutamic acid residues. There are totally 8 Ser-P for αs1-SC and 5 for β-SC. Micro-sized HA was observed to preferentially adsorb β-SC for various concentrations of HA particles. When the concentration of nano-sized HA was below 15 mg/mL, there was a preferred adsorption of αs1-casein over β-SC. The competitive adsorption onto HA surface between αs1-SC and β-SC may be caused by the difference of the number and distribution of Ser-P.关键词：Phosphorylated serine residues;Hydroxyapatite;Protein adsorption;Sodium caseinate;Whey protein isolate
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发布时间：2021-03-19 - 摘要：Polyhydroxybutyrate/carbon nanotubes composite nanofiber membrane was successfully prepared via electrospinning technique using polyhydroxybutyrate and carbon nanotubes as raw materials and chloroform/dimethylformamide blend as co-solvent. The effect of carbon nanotube content on the membrane's morphology and mechanical properties was investigated, and its adsorption performance to heavy metal ions was evaluated. Increasing the content of carbon nanotubes from 0 to 1 wt%, it was found that the average diameter of composite nanofibers decreased from (728±146) nm to (468±89) nm while their specific surface area increased from 27.24 m2/g to 43.45 m2/g; meanwhile, the nanofiber membrane was significantly strengthened with the optimum mechanical performance obtained at the content equal to 1 wt%. A tensile stress of 5.85 MPa was achieved then, which was about 115% improvement compared with the pure polyhydroxybutyrate nanofiber membrane. Good adsorption performance was exhibited by the composite nanofiber membrane for Cu (Ⅱ), Cd (Ⅱ) and Pb (Ⅱ) ions from aqueous solution. Under the optimum pH of 5, the maximum adsorption capacity was measured as about 91.04, 171.05 and 197.03 mg/g for Cu (Ⅱ), Cd (Ⅱ) and Pb (Ⅱ) ions, respectively; the corresponding equilibrium time and adsorption rate were about 50, 60 and 60 min and 1.79, 2.83 and 3.28 mg/g/min, respectively. Langmuir, Freundlich and Temkin models were used to analyze the thermodynamics parameters during adsorption while Pseudo-first-order, Pseudo-second-order and Intraparticle diffusion models were applied for analysis of the kinetics parameters. It was indicated that the adsorption isotherm data fitted well with Freundlich model and the kinetic process matched Pseudo-second order model. Cycle experiments demonstrated that above 87% of initial adsorption capacity could be maintained after 5 times of usage, which suggested the nanofiber membrane's potential of applications in wastewater treatment for the removal of heavy metal ions as a nano-adsorbent.关键词：Polyhydroxybutyrate;Carbon nanotubes;Composite nanofiber;Heavy metal ions;Adsorption
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发布时间：2021-03-19 - 摘要：Inspired by conventional powder coating technology, a novel negative-charged membrane made of thin-film nanofibrous composite (TFNC) with polyacrylonitrile (PAN) nanofibers as the substrate and polyvinyl alcohol (PVA)-sodium alginate (SA) as the hydrophilic barrier layer was successfully developed. The PVA-SA nanobeads were firstly electrosprayed onto the electrospun PAN substrate and then hot-pressed under steam humidification. Water molecules were absorbed from the ambient moisture acted as the "plasticizer" in PVA-SA nanobeads, which could facilitate softening or melting of PVA-SA during the film-formation process. The moistened PVA-SA nanobeads layer would then be pressed imperceptibly into an integrated barrier film on the PAN supporting layer under the gravity pressure of hot plate at a certain temperature. Deposition time (the timespan for PVA-SA electrospraying), moist-curing time, heating temperature (the preset temperature for thermal treatment) and curing time (the timespan for thermal treatment) were carefully adjusted to explore the optimal film-formation condition. And it was found that with the deposition time of 18 min, moist-curing time of 120 s, heating temperature of 60℃ and curing time of 6 min, an integrated and nonporous PVA-SA barrier layer was achieved for TFNC membrane. Finally, the resulting barrier layer was chemically crosslinked by glutaraldehyde (GA) and its compactness could be easily controlled via different crosslinking degree and the composition of crosslinking bath for nanofiltration (NF) applications. The optimized PVA-SA/PAN TFNC membrane (crosslinked by GA with concentration of 0.4 wt%) was negatively charged owing to the carboxyl groups of SA, and it possessed high NF performance in anionic dye filtration. Tests at low feeding pressure of 0.6 MPa showed a permeate flux of 57.1 L/(m 2 h) and rejection ratio above 96.8% for the membrane product toward Acid Blue 90 solutions. Besides, the resultant PVA-SA/PAN TFNC membrane exhibited excellent pressure resistance and antifouling properties during the long-term experiment, and the negatively charged SA played a key role in the NF process.关键词：Thin-film nanofibrous composite membrane;Sodium alginate;Polyvinyl alcohol;Hot-pressing treatment;Anionic dyes removal;Nanofiltration
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发布时间：2021-03-19 - 摘要：In order to improve the ion conductivity and alkaline stability of the anion exchange membranes (AEMs), fluorenyl-containing sequenced poly (aryl ether sulfone) copolymers were synthesized by two-step polymerization, and converted subsequently into quaternized PAES through Freidel-Crafts chloromethylation, amination and alkalization, followed finally by a crosslinking reaction with aliphatic diamines of N, N, N', N'-tetramethyl-1, 3-propanediamine (TMPDA) or N, N, N', N'-tetramethyl-1, 6-hexanediamine (TMHDA). The prepared membranes owned ion exchange capacity around 1.59-2.12 mmol/g and were mechanical ductile. Compared with the non-crosslinked membranes with similar ion exchange capacity, the fundamental properties of the crosslinked membranes, such as solvent resistance, dimension stability, ionic conductivity and other properties, were enhanced. For the crosslinked membranes, the hydrolytic stability under high temperature and the alkaline stability under strong basic conditions were significantly improved. The membranes were crosslinked through two different crosslinking methods, namely, the direct-crosslinking by adding the crosslinking agent to the casting solution and the post-crosslinking by dipping the membranes in the crosslinking agent solution. The effects of the two crosslinking methods on the properties of the membranes were investigated. The results showed that, with the post-crosslinking, the gelation was avoided during the solution casting, while the membranes showed enhanced stability compared to the non-crosslinking ones. Especially, for the membranes post-crosslinked with TMHDA, all the properties were superior to those of the non-crosslinking ones. The membrane of PCL-M (H) (IEC=1.45 mmol/g) showed 99% of water uptake, lower than 15% of size change in-plane direction at 30℃, while with the high ionic conductivity of 23.8 and 82 mS/cm at 30℃ and 90℃ in water, respectively. The PCL-M (H) membrane showed excellent stability, only 7.6% loss in ionic conductivity after treatment in 4 mol/L NaOH solution for 240 h and 5.1% loss in weight after treatment in 100℃ water for 24 h, while 18% and 6.7% losses were found for the non-crosslinking membrane (QPES), respectively. The PCL-M (H) membranes are good candidates for the applications in the fuel cell system.关键词：Fuel cell;Anion exchange membrane;Quaternized poly (aryl ether sulfone);Sequenced polymer;Crosslinking
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发布时间：2021-03-19 - 摘要：Forward osmosis (FO) becomes an emerging and promising platform of membrane separation technology. Nevertheless, FO processing always suffers from poor water flux performance, resulted from internal concentration polarization (ICP). Herein, to improve the hydrophilicity of polysulfone (PSf) membranes, sodium lignin sulfonate (LS) was used as a hydrophilic additive to prepare LS/PSf blend membranes by phase inversion. The LS/PSf blend membranes can serve as the hydrophilic support layer of FO membranes in order to weaken the ICP. The effects of LS content on the structure and the properties of LS/PSf blend membranes were investigated by scanning electron microscopy (SEM), FTIR/ATR spectroscopy, and water contact angle (WCA). It was shown that the finger-like pores of LS/PSf blend membranes became long and narrow, and the WCA of the membrane was reduced to 65° with LS content of 0.4 wt%. Then, thin film composite (TFC) membranes were fabricated by interfacial polymerization on PSf membrane and LS/PSf blend membrane with LS content of 0.4 wt%, which were named TFC and TFC-LS0.4 membranes, respectively. The results from FTIR/ATR spectroscopy and SEM confirmed that polyamide (PA) films were formed with a typical "ridge-valley" surface morphology on both TFC and TFC-LS0.4 membranes. Moreover, the PA film of TFC-LS0.4 membrane was rougher and thicker than that of TFC membrane. Their FO performances were characterized by FO test, where the draw solution was 0.5, 1.0, 1.5 or 2.0 mol/L NaCl solution, and the feed solution was DI water. The water flux and reverse salt flux increased with the concentration of draw solution both for TFC and TFC-LS0.4 membranes. With the same draw solution, TFC-LS0.4 membrane showed a larger water flux and reverse salt flux than TFC membrane. Furthermore, reverse osmosis test was conducted to study the transport properties and structural parameters of FO membranes. It is clear that TFC-LS0.4 membrane presented higher water permeability (A=3.12×10-5 LMH·Pa-1) with smaller structural parameter (S=2010μm) than TFC membrane (A=0.76×10-5 LMH·Pa-1, S=3450μm). It means that the hydrophilicity of LS/PSf blend membranes facilitated the weakening of ICP effects of FO membranes.关键词：Lignin;Polysulfone;Hydrophilic modification;Forward osmosis membrane;Internal concentration polarization
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发布时间：2021-03-19 - 摘要：Allyl-containing benzoxazine (Bala) was synthesized via Mannich condensation reaction using paraformaldehyde, allylamine and phenol as raw materials. The chemical structure of Bala was confirmed by 1H nuclear magnetic resonance (1H-NMR). Ammonium polyphosphate (APP) microcapsules modified by polybenzoxazine (BMAPP) were prepared by in situ ring-opening polymerization of Bala on the surfaces of APP. Fourier transform infrared spectroscopy (FTIR) and static contact angle test showed that Bala polymerized successfully, and enhanced effectively the hydrophobicity of APP. The static contact angle of the BMAPP microcapsules increased to 71.3° from 10.8°. EP/BMAPP flame-retardant materials were prepared by adding BMAPP microcapsules into epoxy matrix (EP). Thermal properties and combustion performance of EP and its composites were investigated by thermogravimetric analysis (TGA), vertical combustion test (UL-94), limiting oxygen index (LOI), cone calorimeter (CONE) and dynamic thermal mechanical analysis (DMA). The results showed that BMAPP microcapsules promoted EP to form high-quality char layer on the surface of the composites, which could serve as a good barrier against heat and oxygen diffusion and played a great role in the combustion process. The LOI value of EP increased from 22.6% to 33.6%, and passed the UL 94 V-0 level with the addition of 10% BMAPP. Residue char of EP/BMAPP-10% was as high as 26.3% at 600℃. Meanwhile, the incorporation of BMAPP microcapsules led to a great decrease in smoke production rate and heat release rate of EP during combustion process, along with an increase in glass transition temperature ( Tg) and storage modulus of EP. The peak of heat release rate (PHRR) of EP/BMAPP-10% reduced from 1247 kW·m-2 to 434 kW·m-2 due to the synergistic flame retardant effects of PBala and APP in BMAPP. Smoke production rate of EP/BMAPP-10% was approximately 67% lower than that of EP. The Tg of EP/BMAPP-10% increased from 169℃ to 173℃ with respect to EP.关键词：Benzoxazine;Microcapsules;Ammonium polyphosphate;Flame retardant properties
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发布时间：2021-03-19 - 摘要：The blending of immiscible polymers has emerged as an effective tool to control the rheological properties of the outcome polymer composite. The properties of the immiscible polymer blends are closely related to their morphology. In situ fibrillation of dispersed phase has been prepared during polymer blending through complex shear and extensional flow, coalescence of dispersed phase domains. In this paper, polypropylene/poly (hexamethylene adipamide) (PP/PA66) in situ microfibrillar composites were prepared by direct extrusion through triangle arrayed triple-screw extruder (TTSE) at low temperatures between the melting points of the two phases. The microfibrillar morphology was adjusted and controlled through changing the PA66 content and processing parameters (temperature and screw speed). The fibrillar aspect ratio increased with PA66 content and the screw speed, owing to better dispersed phase to coalescence and stronger shear and extensional flow. The effect of fibrillar morphology on the rheological properties of PP/PA66 composites was investigated. The results showed that the dynamic storage modulus of microfibril composites at low frequency were apparently higher than that of PP and increased with the fibrillar aspect ratio. Furthermore, the slope of the double logarithmic plot of G' versus ω at lower frequence decreased with the increase in the fibrillar aspect ratio. At the same time, the loss tangent tanδ value decreased and the plots of Cole-Cole circle radius increased with increased fibrillar aspect ratio. This indicated that the system exhibited the characteristics of a pseudo-solid or gel. The presence of a fibrillar network defined by topological (entangled) interactions was expected to create additional and large contributions to the viscoelasticity of the polymer matrix. A multi-frequency plot of tanδ versus the fibril content (Winter-Chambon criteria) was used to reveal the gel point of composite system with different fibrillar morphology. The results showed that the critical gel point was decreased with the fibrillar aspect ratio due to enhanced interconnected microstructures.关键词：In situmicrofibillar composite;Direct extrusion;Microfibillar aspect ratio;Rheological property;Fibrillar network
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发布时间：2021-03-19 - 摘要：The third generation of hydroxyl-terminated aliphatic hyperbranched polyesters were end-capped with stearic acids, in which the polyesters were prepared using 1, 1, 1-trimethanol propane (TMP) as the core and 2, 2-bis (hydroxymethyl) propionic acid (DMPA) as the branched monomer. The crystallization, melting behavior, temperature-induced variation of the conformational behavior and the packing structure of alkyl-terminated chains of the hyperbranched polyesters with different degrees of modification were investigated by wide angle X-ray diffraction (WAXD), differential scanning calorimeter (DSC) and Fourier transform infrared spectroscopy (FTIR). The influence of the terminal alkyl chains on the dynamic viscoelastic behavior of the modified hyperbranched polyesters was studied by rotational rheometer. The results showed that the crystallization of these modified hyperbranched polyesters could be attributed to ordered arrangement of the long-chain end alkanes, and the terminal alkyl chains tended to pack into hexagonal form. With the increase of degree of modification, the diffraction intensity strengthened. Double melting peaks were found in DSC heating curve. The lower melting peak was corresponding to the fusion of the imperfect crystals formed by confined terminal alkyl chains, and the higher melting peak was ascribed to the melting of the relatively well-developed crystals formed by slightly confined terminal alkyl chains. FTIR analysis conducted at different temperatures revealed that, accompanying the melting of the terminal alkyl chains crystallization, the conformation of the terminal alkyl chains of the modified hyperbranched polyesters showed no obvious transition. Upon the melting temperature, the terminal alkyl chains under confined crystallization did not emerge as completely disordered state. These hyperbranched polyesters melts might be arranged in a somewhat ordered state. With the improvement of the degree of modification, the onset of nonlinear viscoelastic region occurred at lower strains for these modified hyperbranched polyesters, and the elasticity of these modified hyperbranched polyesters increased gradually, with the phenomenon of shear-thinning behavior becoming more obvious. These phenomena, appeared in the dynamic rheological experiments, were closely related to the confined terminal alkyl chains of the modified hyperbranched polyesters.关键词：Hyperbranched polyesters;Alkyl-terminated groups;Confined crystallization;Dynamic viscoelastic behavior
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发布时间：2021-03-19
Research Article
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