最新刊期
卷 ， 期 11 ， 2008
- 摘要：The objective of this work was to develop an adsorption resin for removing aromatic acid contaminations of aqueous environment.The macroporous polydivinylbenzene/poly(methyl acrylate) interpenetrating polymer network was prepared by sequential suspension polymerization method; it was then converted to the hydrophobichydrophilic macroporous polydivinylbenzene/poly(N-2-aminoethylacrylamide) interpenetrating polymer network (PDVB/PNAEAM IPN) by aminolysis with ethylenediamine.The hydrophobic PDVB part in PDVB/PNAEAM IPN resin has the ability of adsorption through hydrophobic interaction; on the other hand the hydrophilic PNAEAM part has the ability of adsorption by means of hydrogen bonding.For the adsorption studies salicylic acid was chosen as the representative of aromatic acids,because there is a hydrophobic benzene ring and a hydrophilic hydroxyl group in the molecule.The pore structure,the weak base exchange capacity,the water retention capacity and the swelling ratio of PDVB/PNAEAM IPN resin were measured.The adsorption isotherms of salicylic acid at different temperatures were studied.Isothermal adsorption enthalpy,Gibbs free energy and entropy were calculated according to thermodynamic equations.The saturated adsorption capacity for salicylic acid was up to 46.1 mg/mL (wet resin) according to the dynamic adsorption and desorption experiments.The resin can be regenerated by 4% NaOH.The results of adsorption for salicylic acid indicate that the PDVB/PNAEAM IPN resin may have a promising prospect in separating aromatic acid from waste water in industry.
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发布时间：2021-03-19 - 摘要：The principle of absolute quantification for size exclusion chromatography (SEC) with refractive index-light scattering (RI-LS) dual detectors was discussed with emphasis on the importance of the injected mass of the sample.By the measurement of the response constant of dual detectors for the injected whole sample,the specific refractive index increment dn/dc and the absolute weight average molecular weight (Mw) could be simultaneously determined.The proposed data treatment procedures are first applied to a series of narrow MWD polystyrene (PS) samples for determining the values of dndc and Mw.The experimental relationship between dn/dc and Mw for PS is in coincidence with the theoretical formula derived from the end group effect.The correction of dn/dc when Mw104 must be considered.The proposed method is not only useful for homopolymers,but is also applicable to polymer mixture and blends.Regarding an unlike polymer mixture with a given composition as a single solute,the specific refractive index increment and the absolute weight average molecular weight of the polymer mixture can be measured to decide whether molecular association between the two components happens or not.The method is illustrated by the system of poly(methyl-methacrylate) and polystyrene (PMMA/PS) in THF solution.PMMA chains will partially associate with PS chains to form complexes.The Mw values of PMMA/PS mixtures in THF show a great positive deviation from the linear composition addition rule.The deviation is attributed to the formation of PMMA/PS complex.The complex formation could be described by a simple reaction scheme of nA+mB=AnBm.Analyzing and fitting the experimental data yields:n=3,m=1/3 and an association constant of Ka=4.6×105.
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发布时间：2021-03-19 - 摘要：Magnetic Fe3O4/P(MMA/DVB)(core)-P(St/GMA/DVB)(shell) composite microspheres with coreshell structure were prepared by a twostep method.(1) Preparation of the magnetic cores:First,the magnetic miniemulsion composed of organic ferrofluid droplets dispersed in water was obtained by rapid addition of an oilbased magnetite ferrofluid,with a solid content 60 wt%,into the aqueous solution using DNS-86 (polymerizable surfactant) as surfactant in the condition of ultrasonic emulsification.Then,the copolymerization monomers of methyl mathacrylate (MMA) and divinyl benzene (DVB) were injected directly into the magnetic miniemulsion.Because of their hydrophobic character,once the monomers were added into the emulsion,the methyl mathacrylate (MMA) and divinyl benzene (DVB) would have a high tendency to diffuse inside the organic phase of the ferrofluid droplets to form monomer swelling magnetic miniemulsion,which were supposed to be the main locus for copolymerization.In succession,the temperature was rapidly increased to 70℃ and starting the miniemulsion copolymerization to form uniform magnetic latexes.(2) Preparation of the core/shell hybrid polymeric microspheres:Through varying the feeding amount of styrene (St),glycidyl methacrylate (GMA) and DVB,the core-shell structured microspheres were rationally fabricated by the seed emulsion copolymerization using the above magnetic latex as the core emulsion.This preparation process is convenient and effective.Extensive characterization by X-ray diffraction (XRD),high resolution transmission electron microscopy (HR-TEM),thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) showed that the magnetite content of Fe3O4/P(MMA/DVB) composite microspheres was 84 wt%.The magnetite content of the magnetic composite microspheres with core-shell structure is varied from 20 wt% to 76 wt% by feeding different amounts of monomers.The average diameter of the magnetic seeded microspheres and the core-shell composite microspheres is 150 nm and 350 nm,respectively.The functional epoxy groups on the surface of the core-shell composite microspheres can be further modified to load biomolecules.
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发布时间：2021-03-19 - 摘要：Polyvinyl chloridediethylenetriamine supported palladium complex (PVCDETAPd) was synthesized from polyvinyl chloride via a simple method, and the production cost of the complex was low.PVC-DETA-Pd has good thermal stability,so it can satisfy the high temperature condition of the Heck reaction.XPS analysis shows that two different chemical states of palladium,Pd0 and Pd2+,are existed in PVC-DETA-Pd.The molar ratio of Pd0 to Pd2+ is 1∶1.44. PVC-DETAPd is an efficient catalyst for Heck arylations of aryl bromides (or chlorides),which are cheaper substrates than aryl iodides.The yield of the Heck reaction of bromobeneze and styrene catalyzed by PVC-DETAPd was up to 99% in nitrogen atmosphere at 110℃ and tetrabutylammonium bromide (TBAB) as solvent.The reaction of bromobeneze with styrene was catalyzed efficiently by PVC-DETA-Pd in presence of several kinds of acid-binding agents such as Et3N, Bu3N,Na2CO3 and NaAc.The best result was obtained when tributylamine was chosen as the acid-binding agent.The Heck reactions of substituted aryl bromides with vinyl compounds can also be catalyzed efficiently on proper conditions,the yields of the products were more than 70%.Chlorobenzene reacts with styrene to give the moderate yield of 78%.By substituting the chlorobenzene with 4-nitro chlorobenzene,the yield of the product was increased to 80%.Furthermore,the good reusability of PVC-DETA-Pd was also found for Heck reaction.The yield of the stilbene was 74% even if PVC-DETA-Pd was reused five cycles for the model reaction of bromobenzene and styrene.
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发布时间：2021-03-19 - 摘要：Controlled micro/nanostructures of polyaniline （PANI）were obtained through a chemical oxidative polymerization by changing the concentration of aniline monomer in the presence of citric acid as dopant.It was found that conducting PANI microtubes with square inner cross-section (580～300 nm in diameter and 80 nm in wall thickness) were obtained at a relatively high aniline concentration.When the solution was sufficiently dilute,the polyazane microbars with square cross-section (690～290 nm in side length and 1～40 μm in length) can be made by self-assembly.Structural characterizations of the microbars with square crosssection showed that aniline polymerized product by this method was a new material containing N—N single bonds rather than PANI,which was defined as polyazane by A.G.MacDiarmid.The aniline/citric acid salts are proposed as the templates in the formation of the microtubes with square inner cross-section and microbars with square cross-section based on XRD and SEM measurements.Interestingly,it was found that morphology and molecular structure of the microbars were strongly affected by the reaction time and the concentration of aniline.The molecular structure of the microbars with square cross-section was changed from polyazane to PANI,for instance,when the reaction time increased from 5 h to 168 h.Moreover,the microbars with square cross-section were varied from solid to hollow with square cross-section and which was accompanied by a molecular structural change from polyazane to conductive PANI when the concentration of aniline increased by one order of magnitude (from 1.75×10-2 to 1.75×10-1 mol/L).
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发布时间：2021-03-19 - 摘要：The study presents the low temperature phase transition of compact chains with one end fixed based on the interacting selfavoiding walks (ISAWS) on the square lattice.The simulation is realized by transfer matrix (TM) method.During the tensile process,the average pulling force has an obviously oscillations at T0.1,and the oscillations vanishes with the temperature increasing.Since the compact chain has “frozen conformations” like βsheets,and when about half a layer has been opened,the average pulling force decreases obviously.The results agree well with the conclusions by Sanjay Kumar et al.The average pulling force ,the average free energy and the phase transition for compact chains adsorbed on the neutral surface and the attractive surface are investigated respectively.During the initial tensile process,in order to overcome the adsorbed surface,the average pulling force has a peak value,and this phenomenon is also explained by the free energy.The adsorbed surface can make the available average pulling force decrease,so that the area of collapsed phase decreases.On the other hand,the average pulling force is also influenced by temperature.At the beginning,when the end-to-end distance x12,with the influence of excluded volume effects,the average pulling force decreases with the temperature.When endtoend distance 12≤x≤16,the average pulling force keeps a plateau of a constant force around 0.9 with different temperatures.But with the further extension of the compact chain,when the end-to-end distance x16,the average pulling force increases with the temperature.This result has already been found by Kumar et al.for the biopolymers without considering the attractive surface.With considering the influence of excluded volume effects,when the end-to-end distance x is less than the average size of the coil (without force),the compact chain needs a compressing force instead of a pulling force,i.e. when T=1.0,the endtoend distance x=8,the pull-induced force is compressing force,and comparing with the average compressing forces of compact chains adsorbed on the neutral surface and the attractive surface,the adsorbed surface makes the available average compressing force decreases.These investigations may provide some insights into the phase transition in the forceinduced compact chains.
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发布时间：2021-03-19 - 摘要：Phase structure is one of the important influence factors to the properties of the polymer/elastomer/rigid filler ternary composite.In this paper,aiming to obtain the core/shell microstructure with calcium carbonate (CaCO3) particle as the core and ethylene-propylenediene monomer copolymer (EPDM) as the shell in the ternary composite,the polypropylene (PP)/EPDM/CaCO3 composites were prepared using two techniques:surface modification of rigid filler and processing control.The modified CaCO3 (PPW CaCO3) was prepared by using a patent method,and the modified layer of lower molecular weight polypropylene (PPW) on the CaCO3 surface has the characteristics of chemical bonding.The processing control has a two-step procedure. First,EPDM was compounding in a twinroll mill with raw CaCO3 or PPW CaCO3 followed by pulverization.Secondly,the pulverized EPDM/CaCO3 or EPDM/PPW CaCO3 powder was compounding with PP in a twinscrew extruder.The possible phase structures in the ternary composites were analyzed from the views of thermodynamics by measuring the surface tension of each constitute and calculating the interfacial tension and work of adhesion for all possible PP/EPDM,PP/CaCO3,EPDM/CaCO3 pairs in the ternary composites.The calculation results indicate that there are two kinds of possible phase structures existing in the ternary composites,one is the core/shell structure with CaCO3 particles as the rigid core and EPDM as the soft shell,another is CaCO3 particles and EPDM dispersing separately in PP matrix.However,SEM photos show that the proportions of the two structures in PP/EPDM/CaCO3 and PP/EPDM/PPW CaCO3 composites are different,the core/shell structure mainly exists in PP/EPDM/PPW CaCO3,resulting from the different surface properties of CaCO3.Because of the core/shell structure,the mechanical properties of PP/EPDM/PPW CaCO3 ternary composites are better than those of PP/EPDM/CaCO3 ternary composites.When the content of EPDM is 8 phr and PPW CaCO3 is 15 phr,the mechanical properties of composites are the best.The notched impact strength can reach 14.25 kJ/m2,which is 3.17 times higher than that of the PP matrix.
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发布时间：2021-03-19 - 摘要：A bipolar membrane is a polymeric layered structure composed of a cation ion-exchange layer and an anion ionexchange layer.With respect to commercial applications,a bipolar membrane has high selectivity,low potential drop,acid and base resistance,solvent resistance,a wide pH range and good mechanical strength.mCMC-PEG/mCS-PEG bipolar membrane was prepared by a paste method,which was prepared by a blend of sodium carboxymethyl cellubse-plyethylene glycol (CMC-PEG) and a blend of chitosanplyethylene glycol (CS-PEG),which were modified by Fe3+ and glutaraldehyde (GA) as linking reagents,respectively.FTIR was applied to analysis the function groups of the bipolar membrane.Furthermore,the cross-section SEM photographs of the bipolar membrane illustrated a structure that consists of anion layer (mCS-PEG membrane) and cation layer (mCMCPEG membrane).The charge densities of mCMC-PEG and mCS-PEG solutions were determined by the colloid titration.The water ratio,ion exchange capacity and swelling degree of mCMC-PEG membrane and mCSPEG membrane were investigated.The currentvoltage (I-V) curve across mCMC-PEG/mCS-PEG bipolar membrane was measured.The experiment results showed that CS-PEG and CMC-PEG blends appeared better compatibility and the introduction of PEG was beneficial to enhance the ionic exchange capacity and decrease the swelling degree of membrane.When mass ratio of CMC/PEG was 10/1 and CS/PEG was 2/1,mCMC-PEG layer and mCSPEG layer were agglutinated tightly.The mCMCPEG/mCS-PEG bipolar membrane appeared excellent electrochemical properties and high mechanical strength in acid and alkali solution.Meanwhile TG analysis of mCMC-PEG/mCS-PEG bipolar membranes exhibited a good thermal stability.mCMC-PEG/mCS-PEG bipolar membranes were used as the separator in the electrolysis cell for electro-generation organic acid.
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发布时间：2021-03-19 - 摘要：Poly(cyclohexene carbonate)(PCHC) is one of the few biodegradable polymers maintaining dimension stability over 100℃ due to its high Tg of 115℃,but PCHC is quite difficult for melt processing because of its brittleness.In this work,backbone modification route was proposed by intercalating soft ethylene carbonate segments among the hard cyclohexene carbonate segments,where the terpolymerization of carbon dioxide (CO2),ethylene oxide(EO) and cyclohexene oxide (CHO) was carried out under ternary rare earth metal coordination catalyst prepared from Y(CCl3COO)3,glycerin,and ZnEt2.The terpolymerization was carried out at 70℃ in a 2000 mL autoclave for 10 h.The obtained terpolymers were subjected to 1H-NMR,13C-NMR- experiments for structure analysis,Gel permeation chromatograhy (GPC) was used to determine the number average molecular weight and its polydispersity,and dynamic mechanical analysis (DMA) was used for thermomechanical studies,the mechanical performance was done with a ZWick/Z010 multifunction mechanical testing instrument.The catalytic activity was between 425 g/(mol Zn h) and 691 g/(mol Zn h),depending on the molar ratio of CHO to EO,and the number average molecular weight ranged between 7.2×104 and 7.9×104 ,with polydispersity index changing from 3.17 to 3.57 .The optimal catalytic activity reached 691 g/(mol Zn h) when equal molar ratio of EO and CHO was added,and the obtained terpolymer showed a number average molecular weight of 7.9×104 with polydispersity index of below 3.5. The absorption peaks in 1H-NMR spectra of poly(ethylene carbonate),poly(cyclohexene carbonate) and related terpolymer were assigned.For the terpolymer obtained from equal molar ratio of EO to CHO,heteronuclear multiple-bond correlation (HMBC) experiments showed that alternating linkages between ethylene carbonate and cyclohexene carbonate were only 269% in the terpolymer,and random structure consisting of ethylene carbonate (EC) units and cyclohexene carbonate (CHC) units was predominant.For the terpolymer obtained from equal molar ratio of EO to CHO,the dynamic mechanical analysis (DMA) spectra showed three peaks,one peak at -80℃ was attributed to a second transition in the terpolymer,the another two peaks appeared at 20℃ and 80～100℃ were assigned to the glass transitions of the polymer related to ethylene carbonate segments and cyclohexene carbonate segments,respectively,the existence of two glass transitions at different temperatures indicated that the existence of soft and hard segments in the backbone.Introducing EO as the third comonomer was effective to solve the brittleness of PCHC making it melt processable,moreover,the thermal and mechanical properties of the terpolymer can be adjusted by changing the molar ratio of EO and CHO in comonomers.For the terpolymer obtained from equal molar ratio of EO to CHO,the Young’s modulus at 25℃ was 9957 MPa,and its tensile strength was 271 MPa with elongation at break of 42.3%.When the temperature was raised to 50℃,the Young’s modulus maintained 8687 MPa,and its tensile strength was 15.2 MPa with elongation at break of 576%.As a reference,poly(propylene carbonate) lost mechanical strength at 50℃,the Young’s modulus at 40℃ was found to be 568 MPa,and its tensile strength was 2.1 MPa with elongation at break of 1814.9%.Therefore,by means of terpolymerization of CO2,EO and CHO,a melt processable biodegradable polymer with improved dimension stability at higher temperatures was prepared.
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发布时间：2021-03-19 - 摘要：A novel method for preparation of magnetic composite microspheres was developed by emulsifier-free emulsion polymerization controlled by 1,1diphenylethylene (DPE) as free radical polymerization control agent.This paper reported the synthesis of clean composite microspheres with high magnetite content and carboxylic surface by this method.The synthetic strategy is a two-step polymerization.First,some amount of acrylic acid(AA),methyl methacrylate (MMA) and DPE reacted for a few minutes in the presence of persulfate potassium (KPS) as initiator.Subsequently,Fe3O4/SiO2 magnetic fluid prepared by surface modification of Fe3O4 nanoparticles with ethyl orthosilicate was added,and the mixture was further polymerized for another time period.Then the system was cooled down to room temperature.The reaction stopped and a precursor polymer which possessed amphiphilic nature and DPE-capped chains was obtained.One end of the precursor polymer chain was linked to the surface of magnetic fluid through chemical adsorption.This not only improved the hydrophobicity of magnetic fluid surface,which stabilized inorganic particles in oil monomers,but also immobilized the potential active species on the surface of nanoparticles.Secondly,the system was heated to a desired temperature and styrene(St) was added to the mixture.The DPEcontaining precursor polymer was activated and initiated the monomer polymerization on the surface of magnetic nanoparticles.After a desired reaction time,some amount of acrylic acid was introduced to the system and polymerized for additional hours.At last Fe3O4/SiO2/P(AA-MMA-St) magnetic composite microspheres were obtained.The chemical structure of magnetic fluid and composite microspheres were characterized by Fourier transform infrared spectrometer (FTIR),X-ray photoelectron spectra (XPS).The carboxyl content on the surface of composite microspheres was determined by conductometric titration.The thermoanalysis of composite microspheres was conducted by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA).The morphologies of magnetic fluid and composite microspheres were observed under a transmission electron microscope (TEM).Particle size determination of composite microspheres was conducted on a laser particle analyzer.The magnetic properties of all magnetic particles obtained were evaluated by using a vibrating-sample magnetometer (VSM).The results of FTIR and XPS indicated the hydrolysate of ethyl orthosilicate formed SiO2 layers on the surface of Fe3O4 nanoparticles.The SiO2 layer made the saturation magnetization of Fe3O4/SiO2 fall by 3.7% in contrast with Fe3O4,but it prevented Fe3O4 from reacting with —COOH group,and improved the magnetic property of Fe3O4/SiO2/P(AA-MMA-St) by 28% compared with Fe3O4/P(AA-MMA-St) obtained at the same experimental conditions.The TEM observation suggested the composite microspheres possessed core-shell structure.The particle size measurements disclosed the average diameter of composite microspheres was 422 nm and the particle size distribution was narrow,which indicated all the monomers polymerization on the surface of magnetic nanoparticles were controlled effectively by DPE.The TGA analysis revealed the content of inorganic particle (Fe3O4/SiO2) was about 40% in composite microspheres.The magnetic property evaluation indicated the saturation magnetization of Fe3O4/P(AA-MMA-St) was 34.850 emu/g.The conductometric titration result demonstrated the content of carboxyl group on composite microspheres surface was 0.176 mmol/g.DSC analysis showed the glass transition temperature of Fe3O4/SiO2/P(AA-MMA-St) increased by 8.9℃ compared with the copolymer of P(AA-MMA-St),which confirmed there was interaction between the core of magnetic nanoparticles and the shell of copolymer.
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发布时间：2021-03-19 - 摘要：The purpose of this work is to decrease the amount of boron trifluoride diethyl etherate (BFEE) usually used during the electrochemical polymerization and enhance the stability of as-formed polymer films. The mixed electrolyte of tetrahydrofuran (THF) and BFEE was used because THF can form a new complex with BF3 which is more stable than BFEE and it also can be the solvent for many kinds of aromatic compound which can be electropolymerized.To increase the ionic conductivity of the mixed electrolyte,Bu4NBF4 was introduced.The ionic conductivity of THF containing 18% BFEE (by volume) and 0.1 mol#8226;L-1 Bu4NBF4 was measured to be 1.25×10-3 S#8226;cm-1.In this medium,highquality polycarbazole (PCZ) films were electrosynthesized successfully by direct oxidation of 0.05 mol#8226;L-1 carbazole.The oxidation potential of carbazole in this medium was measured to be only 0.92 V versus SCE,which was much lower than that determined in acetonitrile containing 0.1 mol#8226;L-1 Bu4NBF4(1.36 V versus SCE).PCZ films obtained from this medium showed good electrochemical behavior,with electrical conductivity of 7.0×10-3 S#8226;cm-1.Asformed PCZ films can be partly dissolved in strong polar organic solvents such as dimethyl sulfoxide.For dedoping,PCZ films were treated with 25% ammonia for 3 days.Then,they were dried at 60℃ for 24 h.The UV-Vis spectra of PCZ showed broader absorption bands mainly at 303 nm,implying wide molar mass distribution.In the fluorescence spectra,the emission peaks of polycarbazole appeared at 415 nm,implying the blue-light-emitting property of PCZ.The FT-IR and 1H-NMR spectral investigations of PCZ indicated that electrochemical polymerization of carbazole mainly occurred at 3,6 positions,in well accordance with the literature reported previously.Thermal analyses indicated that PCZ films prepared from this medium own good thermal stability.The successful electrosyntheses of PCZ films in this mixed electrolyte may extend the applications of this mixed electrolyte of THF,BFEE and Bu4NBF4 in the electrochemical science.
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发布时间：2021-03-19 - 摘要：A novel amphiphilic and thermosensitive triblock copolymer of poly(N-isopropylacrylamide)-b-poly(3-benzyloxycarbonyl-L-lysine)-b-poly(ethylene glycol) (PNIPAM-b-PZLL-b-mPEG) with designed molecular weight and narrow molecular weight distribution was prepared.Synthetic procedure included the following steps.(1) Amino-terminated PNIPAM was synthesized via the free radical polymerization of NIPAM in methanol using 2,2′-azobisisobutyronitrile (AIBN) and 2-aminoethanethiol hydrochloride (AET#8226;HCl) as the initiator and chain transfer agent,respectively.Its molecular weight was calculated by the 1H-NMR-spectra in D2O.(2) The block copolymers,PNIPAM-b-PZLL were synthesized by the ringopening polymerization (ROP) of 3-benzyloxycarbonyl-L-lysine N-carboxyanhydride (Z-Lys-NCA) with PNIPAMNH2 as a macroinitiator.Their structure was confirmed by the 1H-NMR spectra.The molecular weight and molecular weight distribution of PNIPAM-b-PZLL were characterized by GPC analysis in THF.The relatively narrow polydispersity of the obtained PNIPAM-b-PZLL could be explained by the living character of the ROP of NCAs initiated by primary amine hydrochlorides which avoided the side reaction called “active monomer" mechanism.Generally,the molecular weights could be controlled by the feed molar ratios of monomer to maroinitiator.(3) For preparing the triblock polymers,PNIPAM-b-PZLL-b-mPEG,it was necessary to convert the terminal hydroxyl group of mPEG of different molecular weight (2000 or 5000) into carboxyl group by succinic anhydride.Its 1H-NMR spectra showed this was a high efficiency reaction.Then the triblock copolymers were obtained by the condensation reaction between carboxyl-capped mPEG and aminocapped PNIPAM-b-PZLL in the presence of dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP).The 1H-NMR confirmed their structure.Based on the integration ratio,their relative amount in the copolymer was calculated.And their Mn(NMR) agreed well with the theoretical numberaverage molecular weight.GPC analysis in THF revealed a monomodal and symmetric peak which showed the successful synthesis of target copolymers.All the molecular weight distributions (Mw/Mn=1.11～1.20) were relatively narrow.The triblock copolymer could selfassemble into micelles in aqueous solution with hydrophobic PZLL as the core- and hydrophilic PNIPAM and mPEG as the corona.Its critical micelle concentration (CMC) was measured by a fluorescence spectra technique using pyrene as a probe.The CMC decreased with the increase of PZLL content and increased with the increase of PEG content.Dynamic light scattering (DLS) analyses of triblock copolymer micelles revealed their size of less than 100 nm and narrow size distribution.It is well-known that PNIPAM homopolymer dissolved in cold and dilute aqueous solution but gets insoluble at ca. 32℃ due to its lower critical solution temperature (LCST) phase behavior.When the temperature was above the LCST,the PNIPAM undergoes a reversible phase transition caused by the coil-to-globule transition and becomes more hydrophobic.So changing temperature will influence the stability of micelles.As anticipated,the micelles aggregated at temperatures above LCST when the Mn of mPEG was 2000.That is probably that the mPEG2000 could not prevent the intermicellar hydrophobic interaction.However,no obvious aggregation of micelles was found at temperatures above LCST when the Mn of mPEG was 5000 because the hydrophobic interaction between the micelles was prevented by mPEG5000 effectively.
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发布时间：2021-03-19 - 摘要：The precipitation polymerization of acrylonitrile for preparing high isotactic polyacrylonitrile (PAN) by using dibutylmagnesium as initiator was carried out in xylene solvent. The kinetics of precipitation polymerization was studied. High isotactic PAN was prepared by using several monomer concentrations (0.288～0.496 mol/L), initiator concentrations (0.00568～0.01135 mol/L) and different polymerization times (15～60 min). The kinetic model was proposed from the sub-micro process of precipitation polymerization. A kinetic equation was then deduced by using the concept of total ways of the primary precipitate aggregates (F［P］). The final firstorder kinetic equation ln［1/(1-α)］=kt where α represented conversion rate and t polymerization time was based on Taylor series expansion of F［P］ and the relation between F ［P］ and precipitation amount. ln［1/(1-α)］ and polymerization time (t) had a linear relationship which proved the first-order kinetic equation was in good agreement with the experiment data. The reaction rate constant k was decreased with the concentration of monomer increased. It suggested that the initiator was diluted by monomer which made the total ways of the primary precipitate aggregates decreased and then k decreased. On the contrary,k was increased as the concentration of initiator increased. However, the reaction orders with respect to monomer and initiator were both found to be 1.0 in the acrylonitrile’s precipitation polymerization. The kinetic equation of the precipitation polymerization was Rp=k0［M］1.0 ［I］1.0.
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发布时间：2021-03-19
Research Article
- 摘要：Welldefined dendrimer,poly(amido-amine) dendrimer (PAMAM),was surface engineered via biomimetic phosphorylcholine(PC) to achieve a potential biocompatible candidate for gene delivery.PAMAM dendrimer is proven to be an efficient gene carrier itself,but it is associated with certain problems such as low water solubility and considerable cytotoxicity.PC-based polymers were designed with mimicking the biomembrane structure and widely used to improve the biocompatibility of various medical devices.Surface modification of PAMAM via phosphorylcholine is conceived to improve the biocompatibility of PAMAM.Generation 5.0 PAMAM dendrimer (G5) has been synthesized by divergent method with ethylenediamine as core.The surface of PAMAM was conjugated with PC groups via the Michael addition reaction between the 2-acryloyloxyethyl phosphorylcholine (APC) and the primary amines located on G5-After dialysis in distilled water and lyophilization,the PC modified PAMAM G5 (G5-PC) was obtained.The success of the PC modification of PAMAM was followed with FTIR and 1H-NMR characterigzation.The average primary amino group numbers of the G5 and G5-PC were followed through 1H-NMR and potentiometric titration.While there were 106 primary amine groups on the native PAMAM,the surface modification of PAMAM resulted in approximately 50 PC groups on the G5-PC and 56 primary amine groups were remained.Cell viability tests and morphology observation indicated that the cytotoxicity of G5-PC was much lower in ECV304 cell lines in comparison with that of native PAMAM G5.The biomimetic PC modification sufficiently improved the biocompatibility of the native G5.The surface charges of the G5 and G5-PC were measured via zeta potential measurements,and their zeta potentials were +22.4 and +33.4 mV, respectively.The positive surface charges allowed the G5-PC to form complexes with DNA as indicated by particle size analysis.These results suggested that the biomimetic phosphorylcholine surface engineered poly(amido-amine) dendrimers could be an excellent biocompatible candidate for gene delivery systems.
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发布时间：2021-03-19 - 摘要：A polyimide containing main-chain chalcone groups and hydroxyl sidegroups was synthesized.In the synthesis,1,3-dioxoisobenzofuran 5-carbonyl chloride was obtained by the reaction between 1,2,4-benzenetricarboxylic anhydride and SOCl2.1,3-Bis(4-(2-hydroxyethyl) phenyl)-prop-2-en-1-one was synthesized by the nucleophilic substitution reaction between 2-chloroethanol and 1,3bis(4-hydroxyphenyl)-prop-2-en-1one,which was synthesized from the ClaisenSchmidt condensation of 4hydroxybenzaldehyde and 1-(4-hydroxyphenyl)ethanone.The new dianhydride monomer containing chalcone group was prepared by reactions between 1,3-dioxoisobenzofuran-5-carbonyl chloride and 1,3-bis(4-(2-hydroxyethyl)-phenyl)prop-2-en-1one.The polyimide was obtained by polycondensation of the dianhydride monomer with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and subsequent thermo imidization.The chemical structure and properties of the polyimide were characterized by 1H-NMR,FTIR,GPC and thermal analysis.The number average molecular weight (Mn) of the polyimide is 27310 with a polydispersity index of 1.55.The glass transition temperature (Tg) of the polyimide is 207℃ obtained from the DSC thermogram.The thermal degradation temperature (Td) is 382℃ measured at the point with a weight lost of 2.5% from the thermogravimetric curve.The polymer shows good solubility in aprotic polar organic solvents such as DMF,DMAc and THF.The polyimide has an absorption maximum at 342 nm due to the chalcone group.Upon the UV light irradiation,the polyimide can undergo sensitive ［2+2］ photocycloaddition reaction.After UV light irradiation with the dose of 20 J/cm2,the absorbance band at 342 nm disappears completely,and the film is insoluble in DMF.The polyimide synthesized in this work can be expected for applications as photoimagable materials and others.
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发布时间：2021-03-19 - 摘要：The synthesis and characterization of a liquidcrystalline triblock copolymer containing ethoxycarbonylazobenzene units were described.The methacrylate containing ethoxycarbonylazobenzene functional group,6-(4-(4-ethoxycarbonylphenylazo)phenoxy)hexyl mathacrylate (C6ET),was prepared as the monomer.For the synthesis of the triblock copolymer,a macro-initiator was prepared by the reaction of PEO2000 with an excessive amount of 2-bromoisobutyryl bromide catalyzed with triethylamine.The ABA triblock copolymer (PC6ET-PEO-PC6ET) was obtained by ATRP of C6ET with the macroinitiator.For comparison,a homopolymer PC6ET also was obtained by the atom transfer radical polymerization (ATRP) of C6ET.UV-Vis spectroscopy,FT-IR spectroscopy,1H-NMR analysis and GPC measurements were used to characterize the structure and molecular weights of the products.Thermal analysis,optical microscopy and X-ray diffraction were used to characterize the LC phase types and phasetransition temperature.Results show that PC6ET is a liquid crystalline polymer with smectic phase.The clearing temperature of the homopolymer was 20℃ higher than the corresponding azo polymer with alkoxyl groups,which indicated the effect of substitutents on the liquid crystalline properties.The cleaning temperature of the ABA triblock copolymer PC6ET-PEO-PC6ET was slightly lower than that of the homopolymer.The phase transition temperatures of the homopolymer and block copolymer were determined to be Cr 70 s 153 i 151 s 58 g,and Cr 65 s 139 i 139 s 48 g (℃) respectively.The azobenzene-containing block copolymer could be used as a potential photoinduced self-assemble system.
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发布时间：2021-03-19
Research Bulletin
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