最新刊期
卷 ， 期 7 ， 2014
- 摘要：Graphene has drawn numerous attention due to its intriguing and unparalleled physical properties. Graphene and its derivations have promising applications in rubber composites because these atomically thin carbon sheets can significantly improve physical properties of host rubber at extremely small loading. The present work first reviews the synthesis and functionalization of graphene. Then the preparation methods of the graphene/rubber composites are disclosed, and the thorough investigations on the properties as well as the structures of graphene/rubber composites are discussed. Lastly, the future perspectives on preparing and characterizing graphene/rubber composites are proposed.关键词：Rubber;Graphene;Nanocmposites
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发布时间：2021-03-19 - 摘要：Graphene,a two dimensional nanomaterial with the layer thickness of only one atom,has aroused tremendous research interests due to its outstanding properties.A new type of nanodielectrics with superior performance can be achieved by introducing graphene nanosheets into polymeric matrices.This review highlighted some recent research progress on graphene/polymer nanocomposites with high dielectric permittivity.The content of this article included the basic theory of percolation,the interface effect of graphene/polymer on the dielectric properties of nanocomposites.关键词：Graphene;Nanocomposites;Dielectric properties;Percolation theory
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发布时间：2021-03-19 - 摘要：Graphene has a unique oneatom thick two-dimensional structure,large specific surface area,and excellent electronic,optical,thermal and mechanical properties.Graphene can be blended into polymers to form composites through either covalent or noncovalent (e.g.hydrogen bonding,- stacking and electrostatic) interactions.These interactions can increase the dispersibility of graphene in polymer matrices and also can improve the properties of graphene/polymer composites or extend their functions.Several methods including solution mixing,melt blending and in situ polymerization have been developed to prepare graphene/polymer composites.These composites can be processed into thin films by solvent evaporation,casting,vacuum filtration or layer-by-layer assembly.Graphene/polymer composite films have potential applications in highstrength structural materials,supercapacitors,photovoltaic devices,lithium ion batteries and sensors.In this review,we summarize the recent advancements on the preparation and applications of graphene/polymer composite thin films.The issues and challenges that remain in this field were also be discussed.关键词：Graphene;Graphene oxide;Polymer;Composite;Application
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发布时间：2021-03-19
Reviews
- 摘要：In this study,the effects of the various control parameters in preparing high quality PS-b-PLLA single crystals as well as PS-b-PLLA/PLLA composite single crystals and their thermodynamic properties in solutions and in the bulk state are reported.Main control parameters including the seeding temperature (Ts) and time (ts),crystallization temperature (Tc) are discussed based on their effects on the size and its distribution,shape and thickness of the resulting crystals.In general,increasing Ts and ts lead to larger crystals with narrower distributions.Increasing Tc leads to a morphology transition from lozenge to truncated lozenge.DSC thermal analysis show that while the single crystals in solution have one melting point,the DSC profiles show a significant melting and recrystallization behavior in the bulk state after removing the solvent,which suggests that the crystals are under a metastable state in the bulk.Interestingly,when crystals are annealed at different temperatures below the onset melting point,the DSC heating profiles show similar initial melting point and the recrystallization process,indicating that the thermodynamic stability of the crystals does not change upon annealing.These results further suggest that the lamellar thickening via -relaxation in the PLLA lamellar crystals is prohibited and the high thermodynamic stability of crystals can be achieved only by recrystallization.关键词：Self-seeding technique;Single crystals;Composite single crystals;Thermal stability;DSC
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发布时间：2021-03-19 - 摘要：Controlled/living radical polymerization (CLRP) is one of the most rapidly developing areas in polymer science,and among the various existing techniques,nitroxide-mediated polymerization (NMP) was the first to be proposed.Most researches focused on the development of aliphatic nitroxide while few studies were devoted to the use of aromatic nitroxides in NMP.This paper describes nitroxide-mediated radical polymerization of methyl methacrylate (MMA) in the presence of 4,4'-dimethoxydiphenyl nitroxide (DMDPN) and azobisisobutyronitrile (AIBN).The aromatic nitroxide was synthesized by oxidation of 4,4'-dimethoxydiphenyl amine with oxone under biphasic conditions (CH2Cl2/H2O) in rapid and good yields.The bulk polymerization of MMA was conducted in sealed glass tubes at different conditions.The polymerization kinetics was monitored by gravimetric method while the molecular weight and its distribution of poly(methyl methacrylate) (PMMA) synthesized were determined by gel permeation chromatography.The effects of the nitroxide/initiator ratio and polymerization temperature on the polymerization kinetic,molecular weight and polydispersity index (PDI) of PMMA were investigated in detail,and reinitiation reaction experiment was conducted to verify the chain-end activity.The results showed that in this polymerization system,as the DMDPN allows delocalization of the single electron through the aromatic ring,the side reaction of -H transfer from the propagating macroradicals to the free nitroxide which would hinder the propagating process,was neglected and the chain propagation in MMA polymerization could be efficiently controlled.Molecular weight of PMMA increased linearly with monomer conversion at different DMDPN/AIBN ratios and temperatures which was different from common radical polymerization.The PMMA could be reinitiated which showed the characteristics of controlled/living radical polymerization.The polymerization rate was quite fast at low DMDPN/AIBN ratios and an induction period appeared when the ratio was too high.At the DMDPN/AIBN ratio of 1.6,the PDI was the lowest and the curve of ln(M0/M) versus time was a straight line which crossed the coordinate origin.The polymerization rate increased and PDI decreased as the polymerization temperature increased.MMA polymerization could even been operated at 70℃ though the PDI was relative higher.关键词：Nitroxide free radical;Methyl methacrylate;-H transfer reaction;Controlled/living radical polymerization
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发布时间：2021-03-19 - 摘要：Poly(L-lactide) has derived extensive attention as a most promising biodegradable plastics with the excellent physical and mechanical properties.But it's so stiff and brittle for room temperature applications that restrict its wide applications.This work focused on NBR as toughening agent,adding MAH or DCP or the combination of MAH/DCP as the compatibilizer to increase the compatibility.We found that,by adding DCP only,the toughening system has the optimal mechnical properties,the elongation at break and the impact strength were improved by more than 60 times and 5 times respectively,compared with pure PLLA.This method is simple and operable.For understanding the toughening mechanism in depth,we use polarizing optical microscope and transmission electron microscope toinvestigate the morphology of the blends.It was found that the system of PLLA/NBR/DCP has the smallest dispersed size and the uniform state.Also the interface is fuzzy which symbolizes the good compatibility.Besides,the PLLA spherulite is small and uniform.All the factors above lead to the good toughness.The fast crystallization rate is beneficial to the stability of the products.Based on the mechanical properties and the morphology of the blends,we discussed the toughening mechanism of PLLA/NBR.关键词：PLLA;Crystallization;NBR;Toughening;Compatibilizer
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发布时间：2021-03-19 - 摘要：Cyclic poly(n-butyl acrylate)-block-poly(methyl methacrylate) (cyclic-PBA-b-PMMA) can be synthesized successfully by the combination of ATRP and click reactions.The cyclic copolymers were obtained by the intramolecular cyclization reactions between the linear precussors at high dilution.The chemical structures,molecular weights and molecular weight distributions of the cyclic block copolymers obtained were well characterized by Fourier transform infrared spectroscopy,nuclear magnetic resonance spectroscopy and gel permeation chromatography.The thermal properties of these cyclic block copolymers and their linear counterparts were characterized by differential scanning alorimetry and thermogravimetric analysis.It is interesting that the cyclic block copolymers have similar glass transition temperatures but higher degradation temperatures compared to their linear counterparts.The morphologies of the prepared samples were investigated via transmission electron microscopy.Unlike the linear block polymers,the cyclic block copolymers exhibited unique morphologies.Obviously,the cyclic block copolymers displayed a continuous dispersed morphology,and the dispersed phase had a worm-like structure.Meanwhile,nano-scaled phase separation was also observed between PBA and PMMA phasees.By means of annealing above the glass transition temperatures of the two blocks,PBA and PMMA,both linear and cyclic copolymers possessed well ordered nano-structures,and the size of these separated domains increased after annealing.关键词：Click chemistry;ATRP;Cyclic polymer;Azide/Alkyne;Phase separation
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发布时间：2021-03-19 - 摘要：The biodegradable spun-bonded non-woven fabric slices of poly(propylene carbonate) (PPC)/compatibilizer/polypropylene (PP) were prepared by melt blending.Three different compatibilizers were used in this study:maleic anhydride (MAH),polypropylene grafted with maleic anhydride(PP-2) and polypropylene grafted with maleic anhydride and styrene (PP-g-(MAH-co-St)),and the effects of these three compatibilizers on the performance of slices were studied.The results shown that the optimal contents of MAH,PP-2 and PP-g-(MAH-co-St) were 1%,3% and 8%,respectively.When the weight ratio of PPC:PP was 70:30,the tensile strengths of slices were 20.16,21.37 and 26.34 MPa,MFRs were 81.6 g/10min,103.6 g/10min and 46.4 g/10min,T-5% increased by 50.5 K,10.0 K and 28.0 K with the optimal contents of MAH,PP-2 and PP-g-(MAH-co-St) respectively.SEM analysis results shown that the slices with compatibilizers became smoother,had less depressions and cavities,the 30 days degradation rate of slices with the compatibilizers were more than 3.12%.Ring-opening reactions between the anhydride functional groups of PP-g-(MAH-co-St) and PPC were showed by FTIR and 1H-NMR spectra,so the compatibility and comprehensive performance of the slices were improved.The mechanical,thermal,morphological and degradable properties can be impoved by adding the compatibilizers.关键词：Biodegradable;Poly(propylene carbonate);Polypropylene;Compatibilizer;Spun-bonded;Nonwoven fabric
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发布时间：2021-03-19 - 摘要：A practical way to synthesize polyaniline nanotubes was developed using ammonium persulfate (APS) as the oxidant in the absence of any templates and acidic dopants.The structure,morphology and property of the product were characterized by FTIR spectrometry,UV-Vis spectrophotometry,transmission electron microscopy and X-ray diffraction.Polyaniline nanotubes with the outer diameter of ca.80 nm,inner diameter of ca.10 nm and the length of 26 m were obtained with the aid of ultrasonic irradiation.Due to the protons produced during the polymerization,the pH value of the solution decreased with the increasing polymerization time and the polymerization rate increased with the aniline concentration.However,the morphology of polyaniline was irrelevant to the aniline concentration,but affected by the molar ratio of aniline to APS.Ultrasonic irradiation played an important role in the formation of polyaniline nanotubes.It prevented the rapid agglomeration of spherical micelles and made the self-assembly of micelles more orderly.As a result,polyaniline nanotubes can be synthesized at a higher aniline concentration.The conductivity of polyaniline was determined to be 510-3 Scm-1.关键词：Polyaniline;Nanotube;Template-free method;Morphology
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发布时间：2021-03-19 - 摘要：A novel testing approach,freezing point depression of solvent in the swollen vulcanizate,is acquired to estimate the effect of crosslinking network structure,i.e. mesh size and crosslinks dispersion,on the mechanical properties of natural rubber vulcanizates cured by three different accelerator systems in details.No evident discrepancy is found in the crosslinking densities of vulcanizates cured with TU or STU or CZ only,indicating thiourea only accelerates vulcanization process and the sulfur atom of thiourea does not contribute to the sulfur crosslinking in the matrix.Results from freezing point depression tested by DSC measurements show that for solvent trapped within the crosslinking network of vulcanizates cured by STU its freezing point depression is the lowest and its full width at half maximum(FWHM) is the highest among the testing samples,indicating that the incorporation of STU facilitates the formation of a larger network mesh size and a more heterogeneous network in the vulcanizates.Furthermore,the total crystal index (CI) of all vulcanizates induced by stretching is almost the same,i.e.,the effect of total CI on the mechanical properties of vulcanizates can be ignored.By eliminating the effect of crosslinking density and CI on the mechanical properties of vulcanizates,the tensile strength of vulcanizates cured by STU reaches the maximum values,which could be originated from a larger network mesh size and a more heterogeneous network that favors the relaxation of stress and orientation of rubber molecules and crystallization under stretching.关键词：Freezing point depression;Crosslinking network structure;Mechanical property;Rubber;Crosslinking density
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发布时间：2021-03-19 - 摘要：An alkaline quaternized polyacrylonitrile (PAN) based heterogeneous catalyst was prepared and characterized with the purpose of producing biodiesel by transesterification.The PAN was modified by the following three steps:reduction,quaternization and alkalization.The various studies were carried out to evaluate the impact of time,temperature and reactive loadings on reduction and quaternization and to optimize the reaction conditions.In the reduction of nitrile groups to amine groups in the presence of lithium aluminium hydride,both reduction agent loadings and reaction time corresponded to reduction efficiency.In the quaternization step,2,3-epoxypropyltrimethylammonium chloride (EPTAC) as the quaternary ammonium agent was introduced because its reactive epoxy can be grafted with amine group easily.The exceed loadings of EPTAC can improve the amount of alkali significantly which can reach to 0.8034 mmol/g.The modified polymer is characterized by FTIR,XPS and DSC respectively to obtain chemical structure information.The heterogeneous catalysts were applied for transesterification.As a result,at 333 K and with the catalyst loading of 2.0 meq(OH-)/g oil,the biodiesel conversion is up to 64.7%.关键词：Polyacrylonitrile;2,3-Epoxypropyltrimethylammonium chloride;Transesterification;Alkaline heterogeneous catalyst
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发布时间：2021-03-19 - 摘要：Poly(vinyl alcohol)/gelatin/nano-hydroxyapatite (PVA/Gel/n-HA) composites were prepared based on solid state shear milling technology (S3M) and plasticization of gelatin obtained by in situ degradation of collagen during extrusion.The structure and thermal-processing properties of the composites were characterized by scanning electron microscopy (SEM),Fourier transform infrared spectroscopy (FTIR),differential scanning calorimetry (DSC),thermogravimetric analysis (TGA) and high pressure capillary rheometry.The results showed that n-HA particles were well dispersed in PVA based matrix by S3M technology.And strong hydrogen bonds formed between PVA and Gel,which may replace the self-inter and intra hydrogen bonds of PVA.The hydrogen bonds not only improved the thermal stability of PVA and increased the initial thermal decomposition temperature (287.6℃) of PVA/Gel/n-HA composite,but also decreased the crystallinity degree (about 24.5%) of PVA so that the melting point (130.5℃) was much lower than its initial thermal decomposition temperature,obtaining the thermal processing windows over 140 K.The gel significantly reduced the apparent viscosity of PVA/n-HA composites and improved the thermal processing properties,offering a new way to prepare PVA/n-HA bioactive composite.关键词：Poly(vinyl alcohol);Nano-hydroxypatite;Gelatin;Thermal processing
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发布时间：2021-03-19 - 摘要：N-isopropylacrylamide (NIPAM) was copolymerized with -acryloyl-L-Lysine (ACRLLY) using N,N-methylenebisacrylamide (BA) as crosslinker through surfactant-free emulsion polymerization to prepare temperature-sensitive microgels containing free amino acid in side chains.Transmission electron microscopy (TEM),dynamic light scattering (DLS) technique and turbidimetric method were employed to characterize the morphology and the volume-phase transition temperatures (VPTT) of microgels prepared.TEM results shows that the microgels have regular spherical morphology and the size of microgels decreases with the increase of the content of ACRLLY.DLS and turbidimetric analysis indicate that the size of microgels has monodisperse narrow distribution and the size of the microgels decreases with the increase of temperature indicating that the microgels have apparent VPTT.the VPTT of the P(ACRLLY-co-NIPAM) microgels can be successfully tuned by changing the content of the hydrophilic comonomer ACRLLY,and the VPTT of the microgels increases almost linearly with the feed ratio of ACRLLY.The Doxorubicin (DOX) delivery of microgels indicates that the microgels release 56% DOX uptaked at 20℃ and 73% at 37℃ in 12 h.However the microgels release 73% DOX uptaked at 37℃ in 13 h under the pH 7.4 and almost completely release under the pH 4.5.The above-mentioned results shows that the microgels prepared have excellent drug delivery property in different temperature and pH conditions.关键词：N-isopropylacrylamide;Microgels;Free amino acid;Temperature-sensitive;Drug delivery
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发布时间：2021-03-19 - 摘要：Polyimide/nano-MgO composites without using any coupling agents or surface modifiers were prepared successfully by direct dispersing nano-MgO particles into the polyamic acid solution followed by spin coating and thermal imidization.The structures and properties of the composites were characterized by means of Fourier transform infrared spectroscopy (FTIR),X-ray diffraction (XRD),scanning electron microscopy (SEM),Ultraviolet-visible spectroscopy (UV-Vis),thermal gravimetric analyses (TGA) and nano-scratch test.The results showed that nano-MgO particles with average size of ca.20 nm were well dispersed in the polyimide matrix,and the compatibility between the organic and inorganic components was good.The as-prepared composites exhibited excellent optical transparency in the visible region and good UV-shielding properties in the near ultraviolet region.The UV-shielding properties of the composites increased with increasing amount of nano-MgO.It was found that the anti-scratch properties of the composites were enhanced substantially with the addition of nano-MgO.Under a scratching force of 100 N,the scratching depth dropped from 57.4 nm of pure PI to about 10 nm of PI/nano-MgO composites,and the width of the scratches also decreased significantly.Although the thermal stability of the composites was slightly inferior to pure PI,they still possessed fairly good thermal stability under the temperature of 300℃.关键词：Polyimide;Nano-MgO;Composite;Nano-scratch
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发布时间：2021-03-19 - 摘要：(Imino-1,4-cyclohexylenemethylene-1,4-cyclohexyleneiminododecanedicarboxyl)-co-(iminohexylimioheanedicarboxyl) copolymers (PACM12-PA66) were prepared by using 4,4'-diaminodicyclohexyl methane,dodecanedioicacid and hexanedicarboxylhexanediamino salt as the comonomers.A series of PACM12-PA66 copolymers with various PACM12 contents were prepared,and their optical and mechanical properties were studied.The results show that,when the PACM12 content was higher than 40%,the copolymer materials were transparent within the wavelength of visible light (400~800 nm).The high transparency of the transparent materials didn't decrease after heat treatment.The refractive index of the copolymers was not relative to the PACM12 content,verifying that the copolymer with PACM12 content higher than 40% had similar crystal structure,so that there was not obvious difference of refractive index among the materials.The WXRD results showed that the crystal size of copolymer materials became larger,and the crystal became more perfect as the PACM12 content decreased,while the degree of crystallinity first decreased and then increased.All of the results tested by DSC and WXRD described that the transparent copolymers with PACM12 content at 40%,75% and 100% owned a special crystal behavior,the quenched materials were almost amorphous then turned to microcrystal structure after being heat treated; while the copolymer with 34% PACM12 was easily crystallized,as a result the material lost its transparency and became opaque.Both tensile strength and impact strength of the copolymer materials are gradually improved with increasing PACM12 content.For copolymer materials with 40% PACM12 content,the tensile strength (64.28 MPa) increases by 40% and the impact strength (14 kJ/m2)increases by 33% than those of PACM12.关键词：Polyamide;Transparency;Mechanical property;Copolymerization
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发布时间：2021-03-19 - 摘要：Cobalt porphyrin chromophore was doped into soluble polyimide matrix and electrospun into nanofibrous membrane for rapid detection of trace amount of aniline vapor.Smooth and uniform cobalt porphyrin-functionlized nanofibers were obtained through electrospinning process,which indicated that the cobalt porphyrin group did not make the electrospinning conditions and process change.The cobalt porphyrin was highly loaded and uniformly distributed in the obtained nanofibrous membrane and preserved typical photophysical properties of cobalt porphyrin chromophore.When the nanofibrous membrane was exposed to aniline vapor,a distinct UV-Vis spectrum response could be observed.And the UV-Vis spectrum showed regularly change with increasing concentration of aniline vapor,which made the aniline vapor detection achievable.The spectrophotometric response of the nanofibrous membrane was attributed to the formation of the cobalt porphyrinaniline complex upon axial coordination.UV-Vis spectrum was used to further study the detection limit of the nanofibrous membrane toward aniline vapor and the result was found to be 7.82 mg/m3.The sensing membrane also has the advantages of good reproducibility and reusability,it could be seen that the UV-Vis spectrum of the nanofibrous membrane remained nearly unchanged after five cycles of aniline vapor exposure and N2 regeneration.关键词：Cobalt porphyrin;Polyimide;Electrospinning;Aniline;Detection
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发布时间：2021-03-19 - 摘要：Macroinitiator Br-PBA-Br was synthesized via atom transfer radical polymerization with activators regenerated by electron transfer (ARGET ATRP) using the bifunctional initiator and low concentration of complex catalyst composed of inexpensive ligand PMDETA and Cu(Ⅱ)Br2(0.02% molar fraction of monomer).The effects of reaction temperature and catalyst dosage on the polymerization rate and controllability were investigated.Then,PMMA-b-PBA-b-PMMA triblock copolymers with narrow polydispersities were prepared via ARGET ATRP initiated by Br-PBA-Br using CuCl2/PMDETA as catalyst.The residual catalyst was separated with cheap diatomite and the residual concentration of cupric ions was reduced to 0.001% weight fraction to polymer.GPC results showed that the number average molecular weight of the prepared triblock copolymers is in the range of 51000~110000 and the molecular weight distribution is below 1.50.The chemical compositions of triblock copolymer determined by1H-NMR were in good agreement with the GPC results.The glass-transition temperatures (Tg) determined by DSC were around -47℃ and 105℃ corresponding to PBA and PMMA,respectively.AFM,DSC,and DMA confirmed the obvious phase separation in the triblock copolymers.The tensile strength of the copolymer films were among 2.7~11.7 MPa and the elongation at break were among 124%~231%,which showed that the tensile strength and elongation at break of the triblock copolymers were adjustable by changing copolymerization composition.PMMA-b-PBA-b-PMMA triblock copolymer with adjustable properties can be prepared successfully by ARGET-ATRP and the problems of high dosage of catalyst and difficulty in removal are solved.关键词：Atom transfer radical polymerization;Residual catalyst;Thermoplastic elastomer;Acrylates;Triblock copolymer
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发布时间：2021-03-19 - 摘要：The Pickering oil-in-water emulsion stabilized by silicon dioxide (SiO2) nanoparticles was used as a template to fabricate novel microcapsules.The shell of this microcapsule was polyurea (PU),which was achieved by the oil-water interfacial polymerization between polypropylene glycol-toluene diisocyanate (PPG-TDI) and diethylenetriamine (DETA).Ethyl phenylacetate (EPA)-isophorone diisocyanate (IPDI) was successfully encapsulated into the microcapsule.It was found the size and distribution of composite microcapsules could be tailored by altering the volume ratio of water and oil.Optical microscope images exhibited that the diameters of composite microcapsules were in a range of 20 to 90 m.From thermal gravimetric analysis (TGA),the encapsulation mass of EPA-IPDI was estimated to be 53 wt%.Scanning electron microscopy (SEM) observation indicated that the capsules had a smooth surface and a uniform thickness of ca.2 m.关键词：Microcapsule;Pickering emulsion;Isophorone diisocyanate;Interfacial polymerization
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发布时间：2021-03-19 - 摘要：A hyperbranched polyethylene-b-poly(methyl methacrylate) block copolymer (HBPE-b-PMMA) was synthesized herein via a tandem polymerization process,in which chain walking ethylene coordination polymerization was first carried out with a functionalized Pd-diimine catalyst to give a telechelic HBPE covalently tethered with a 2-bromoisobutyryl end group (HBPE-Br),then atom radical transfer radical polymerization (ATRP) of MMA was initiated using the HBPE-Br as a macromolecular initiator,rendering the HBPE-b-PMMA copolymer.The ability of the as-synthesized copolymer to noncovalently exfoliate natural graphite (NG) leading to stable graphene solutions in toluene was further examined.The presence of PMMA blocks in the copolymer is well confirmed by the results from proton nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC) analysis.As indicated by UV-Vis spectroscopy test,the resulting copolymer can effectively exfoliate NG in toluene under the assistance of ultrasonication to render stable solutions of graphene with high concentrations up to 0.071 mg/mL.The results from high-resolution transmittance electron microscopy (HRTEM),atomic force microscopy (AFM) and Raman spectroscopy commonly show that the resulting graphene nanosheets are free of structural defects,with a thickness of 2~4 layers.These high-quality,stable graphene solutions in toluene are potentially useful for the preparation and applications of polymer-based graphene nanocomposites.关键词：Hyperbranched polyethylene;Poly(methyl methacrylate);Block copolymer;Graphene solution;Toluene;Noncovalent
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发布时间：2021-03-19 - 摘要：A new and facile air-flow method was employed to prepare block copolymer membranes with different morphology.PS-b-PEO block copolymers were synthesized by atom transfer radical polymerization (ATRP).The molecular characteristics of the block copolymers were confirmed by 1H-NMR,FTIR spectroscopy and gel permeation chromatography (GPC).AFM and SEM were employed to characterize the surface morphology and inner structure of the films.Effects of molecular structure,air-flow velocity,air-flow temperature and substrate affinity on the membrane surface morphology and internal structure were studied.Vertically oriented microphase structure on the top surface of the membrane can be achieved when the PS mass fraction was between 83% and 85%,air-flow temperature was 50℃ and air-flow velocity was 4 m/s.When the liquid film was treated with an air speed outside the range of 3~5 m/s,no regular structure was observed.Similarly,when the air-flow temperature was too high or too low,no regular structure was observed.Substrates with different contact angles were prepared by chemical modification.Results showed that when the films were prepared on silicon substrates with contact angle less than 90 under appropriate air-flow condition,vertical orientation of cylinder nanochannels formed only in the regions at the top and bottom layers of the block copolymer films while irregular structure appeared in the middle part.关键词：Air flow method;Block copolymer membrane;Microphase separation
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发布时间：2021-03-19 - 摘要：Due to the concern on residue toxic metal in biodegradable polycarbonate,environmental friendly aluminum complexes,i.e,bifunctional aluminum porphyrin complexes were prepared by anchoring quaternary ammonium salts to the porphyrin ligand framework.The structures of all the complexes were confirmed by 1H-NMR,13C-NMR and MALDI-TOF analysis.These catalysts exhibited enhanced activity and selectivity for the copolymerization of CO2 and propylene oxide (PO) compared with the aluminum porphyrin/quaternary ammonium salt binary catalyst system.Using complex 1b as catalyst,the influence of reaction conditions such as CO2 pressure,reaction temperature and [PO]/[cat.] ratio etc,on copolymerization behavior was investigated.The TOF (turnover frequency of epoxide to products) of catalyst 1b can reach 1152 h-1 in 5 h at 90℃ under 3.0 MPa,while the resultant copolymer showed a carbonate linkage of 98% and number average molecular weight (Mn) of 42 103,though the PPC selectivity was 68%.When the copolymerization of CO2 and cyclohexene oxide (CHO) was conducted by using catalyst 1b at the same reaction condition,a TOF as high as 621 h-1 was reached,the carbonate linkage of the obtained copolymer was 81% and the number average molecular weight was 8.0 103,while the polymer selectivity was 100%.Additionally,our work also indicates that variation of the quaternary ammonium anion and the axial ligand had dramatic effects on the catalytic activity of resultant complex.关键词：Bifunctional catalyst;Aluminum-porphyrin;Carbon dioxide;Epoxide;Carbon dioxide copolymer
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发布时间：2021-03-19
Research Article
- 摘要：Regenerated cellulose hydrogel membranes were prepared by introducing pre-gelation of the solution into the typical preparation procedure of immersion precipitation phase inversion of cellulose/NaOH/urea aqueous solution.The influences of the pre-gelation temperature,the sulphuric acid concentration and temperature of the coagulation bath on the structure and properties of the regenerated cellulose hydrogel membranes were investigated by static mechanical stretching and SEM.It was found that pre-gelation could effectively improve the mechanical properties of the resultant cellulose hydrogel membranes without obviously changing in the pore structure.The tensile strength of the membrane prepared by pre-gellation at 60℃ for 30 min was 85% higher than that of the control sample obtained without using pre-gelation.Both the increase in the temperature and the sulphuric acid concentration of the coagulation bath resulted in the formation of larger pores in the membranes accompanied with decrease in the mechanical properties.关键词：Pre-gelation;Immersion precipitation phase inversion;Cellulose;Hydrogel;Strength;Porosity
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发布时间：2021-03-19
Research Bulletin
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