最新刊期
卷 ， 期 12 ， 2007
- 摘要：A new type π-conjugated copolymer was obtained by the polymerization of 2,5-dibromothiophene Grignard reagents and 4,4′-diiodoazobenzene through nickel（II） complexes catalyzed cross-coupling reactions.Both monomers and polymer were characterized by（）1H-NMR,FT-IR,UV-Vis and fluorescent spectroscopy,XRD and thermal analysis.The results from FT-IR and（）1H-NMR showed that the copolymer had the structure as expected.The copolymer obtained by this method gives isolated yields of 80%.Intrinsic viscosity [η] of the polymer is about 0.53 dL/g in sulfuric acid at 25℃.The polymers are brown powders and have good solubility in common organic solvents such as dimethyl sulfoxide（DMSO）,dimethylformamide（DMF）,N-methyl-2-pyrrolidone（NMP）,CHCl3 and slightly soluble in tetrahydrofuran（THF）,benzene,toluene etc.The UV-Vis spectra of the copolymer in CHCl3 showed one broad absorption peak at 384 nm,and the PL spectrum gave a peak at 523 nm.This indicates that the polymers have good fluorescence.It was observed that the copolymer was quite sensitive to acids,and the acidichromatic behavior was investigated applying organic acids such as CF3COOH and CH3SO3H.After adding acids,CF3COOH and CH3SO3H,the color of the polymers chloroform solution changed from yellow to deep green or violet.Addition of triethylamine（Et3N） in an equal amount to the acid leads to almost complete return of the original color immediately.XRD spectrum of the polymers revealed that the polymer had no obvious crystalline structure,however,showed somewhat orderly packed structure.The TGA results indicated that the polymer began to decompose above 326℃,having good heat stability.It is expected to be used as polymer materials with electro-optical properties.
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发布时间：2021-08-24 - 摘要：A self-made low frequency vibration injection molding device was adopted to explore the mechanical properties and morphology for iPP injected moldings.The morphology and mechanical properties of samples produced by conventional injection molding(CIM) were used to compare with those obtained by vibration injection molding(VIM).For VIM the main processing parameters are vibration frequency and vibration pressure amplitude,the range of vibration frequency is 0～3 Hz,and the range of pressure vibration amplitude is 0～59.4 MPa.During the injection and pressure holding stages for CIM the injection and holding pressures are always constant,but for VIM an additional pulsing pressure vibration is exerted on the melt in the runner system and mold cavity,causing compression and decompression on the melt and shearing at the melt-solid interface,and it progresses from surface to core of the dumbbell specimen during solidification stage.In this work,the isotactic polypropylene material was plasticized and pumped into the melt chamber by a single screw extruder.During injection and pressure holding stages for the VIM,the melt was vibrated about 25 s in the dumbbell specimen mould and then cooled down in about 20 s.The melt injection temperature and mould temperature are set at 190℃ and 40℃ respectively.The injection pressure for CIM and the base pressure for VIM was 39.5 MPa.The VIM samples were injected at different vibration frequencies and pressure vibration amplitudes,respectively.To prepare VIM samples treated under different vibration frequencies,the vibration pressure amplitude was set at 19.8 MPa,and for VIM samples teated under different vibration pressure amplitudes,the vibration frequency was set at 0.7 Hz.With application of melt vibration technology the mechanical properties of iPP injection moldings were improved.The tensile strength and impact strength increase with the increasing of pressure vibration amplitude,while the elongation at break decreases.The tensile strength increases with increasing frequency in the low frequency range,but the breaking elongation decreases.When the vibration frequency is above 0.47 Hz,the elongation at break begins to increase with increasing vibration frequency,and the tensile strength is also simultaneously improved.Injected at 190℃ the mechanical strength increases from a conventional value of 41.3 MPa to 48.4 MPa obtained at 0.7 Hz of vibration frequency and 59.4 MPa of pressure vibration amplitude,and the corresponding increase percentage is 17.2%.DSC,SEM and WAXD were used to investigate the structure and morphologies of core regions of injection-molded samples.SEM studies show that the core region of samples mainly consists of sperulites,they may deform and orient along the flow direction and decrease their size in the vibration injection process.DSC curves display that the melt peaks of vibration injection moldings shift to high temperatures compared with those of conventional samples,and the maximal increase percentage of crystallinity for vibration samples is 12.1%.WAXD shows that γ-form crystals are obtained easily at low vibration frequencies and large pressure vibration amplitudes.The orientation of sperulites,increased crystallinity and existence of γ-form crystals are beneficial to improvement of the mechanical properties of iPP vibration injection-molded samples.
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发布时间：2021-08-24 - 摘要：The comonomer,N-isopropylacrylamide(NIPAAm),was introduced in the system for synthesis of nanocapules through styrene miniemulsion polymerization by using low molecular weight hydrocarbon as template.The oligomers of poly(N-isopropylacrylamide) dehydrated and separated from water were adsorbed by the droplets of styrene miniemulsion.Due to the thermodynamic force and electrostatic interaction,the oligomer radicals of PNIPAAm anchoring at the interface of droplets make the interface to be the locus of polymerization.Monomers diffused from the internal part of droplets to supply for further polymerization.The nanocapsules can be obtained through the encapsulation of hydrocarbon by the newly-produced polymers separating at the interface of droplets.The morphologies were observed by TEM.The surface tension of miniemusion was measured by a contact angle determinator.The influences on the morphologies of final product such as the amount of NIPAAm,the ratio of monomer and hydrocarbon,the amount of crosslinking agent and the kinds of emulsifier and initiator pair were studied.The results with different amounts of NIPAAm showed that the homogenous nucleation was induced by the excess amount of NIPAAm which was unfavorable to form nanocapsules.With the increase of oil monomer/hydrocarbon ratio the amount of solid particles increased because the solubility of the NIPAAm in the droplets increased which resulted in the formation of solid particles.The nanocapsules with stable shells were obtained through introducing an appropriate amount of DVB.The entry of the oligomer radicals into nanocapsules was influenced by the initiator/surfactant pair depending on the protection ability of surfactants,the steric hindrance of the ionic groups of the surfactant or the electrostatic repellence.关键词：Nanocapsules;N-isoapropylacrylamide;Interfacial polymerization;Crosslink
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发布时间：2021-08-24 - 摘要：The compatibility,thermal property,crystallization behavior and crystal morphology of the poly(lactic acid)/carboxylated polypropylene(PLA/EPP) blends were investigated by using scanning electron microscopy(SEM),thermogravimetric analysis(TGA),differential scanning calorimetry(DSC) and polarizing optical microscopy(POM),respectively.The results suggest that the blends have better compatibility and thermal stability and exhibit no clear glass transition temperature when the content of the PLA component is lower than 50%.The crystal morphology of both components is spherulites,but PLA exhibits smaller and brighter Maltese crosses,while EPP shows bigger and darker Maltese crosses.Moreover, the spherulites of PLA component show regular discontinuous concentric circlelines surrounding the nuclear of the spherulite,which are cracks with a width about 1～2 μm in SEM micrograph caused by internal stress of the spherulite,and there are some microfibers within the cracks.All the blends exhibit three decomposition stages in the TG curves corresponding to the decomposition of the carboxy groups in EPP,PLA component and main chains of the EPP,respectively,and some content of PLA will improve the thermal stability of the EPP component.The DSC thermalgrams of blends exhibit three main melting peaks,while two lower-temperature melting peaks have been found for the carboxylated polypropylene,and the higher-temperature one is for the PLA.During the melt-crystallization process; the blends have two mainly crystallization peaks when the content of the PLA component is greater than 50%.The EPP component in blends acts as a diluent decreasing much of the cold-crystallization temperature of the PLA in melting process, and improves the melt-crystallization behavior of PLA in melt-cooling process.关键词：Poly(lactic acid);Carboxylated polypropylene;Crystal morphology;Crack;Thermal properties
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发布时间：2021-08-24 - 摘要：A random copolymer of（poly（vinyl） acetate-co-isopropenyl acetate）（PVIPA） with number-average molecular weight（Mn） of 9600 and relatively narrow molecular weight distribution（MWD,Mw/Mn=2.03）was prepared by free radical copolymerization of vinyl acetate with isopropenyl acetate using AIBN as initiator.Then,the cationic polymerizations of isobutylene were carried out by using the above copolymer PVIPA as macroinitiator in conjunction with coinitiator TiCl4 in the absence of an external nucleophilic additive.The effects of [TiCl4],[PVIPA],the ageing temperature and time on monomer conversion and initiation efficiency of PVIPA,molecular weight and molecular weight distribution were investigated.Both PVIPA and H2O in the polymerization system would complex with Lewis acid TiCl4 to form the two different active centers（A） and（B）.（A） and（B） initiated the cationic polymerization of isobutylene（IB） in competition and led to PVIPA-g-PIB and homopolymer PIB,respectively.The copolymerization product was extracted by methanol to remove unreacted macroinitiator.The initiation efficiency of PVIPA was dependent on [TiCl4],,the ageing temperature and time.The polymerization could be started under the condition of enough concentration of TiCl4 and the initiation efficiency of PVIPA increased with increases in [TiCl4] and or a decrease in or at lower ageing temperature or for longer ageing time.However,the initiation from（B） increased when TiCl4 was at high concentrationc.The initiation efficiency of PVIPA increased up to around 90% under the appropriate conditions.The graft copolymer PVIPA-g-PIB with Mn of 163700 and polydispersity of 2.17 could be obtained under proper reaction conditions.Furthermore,the initiation efficiency was also increased by introduction of small amount of 2,6-dimethyl pyridine（DMP）.关键词：Cationic polymerization;Graft copolymerization;Macroinitiator;Isobutylene
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发布时间：2021-08-24 - 摘要：In order to optimize reactive processing conditions and synthesize polymer materials according to requirements a kinetic model of free radical polymerization of n-butylmethacrylate(n-BMA) in counter-rotating twin screw extruders was constructed mainly on the basis of the entanglement theory,and then the numerical calculation expressions of the monomer concentration,the monomer conversion,the average molecular weight and the apparent viscosity were deduced.Consequently,the free radical polymerization process of n-BMA in counterrotating twin screw extruders was numerically simulated by means of the finite volume method and an uncoupled semi-implicit iterative algorithm,and then the evolution characteristics and the influencing factors of different variables like monomer conversion,average molecular weight and fluid viscosity were discussed in detail.A comparison of the monomer conversion as well as the weight-average molecular weight between the simulated results and the experimental results shows a nearly good agreement,which indicates that the constructed model is reasonable.关键词：Reactive extrusion;Free radical polymerization;Chemorheology;Numerical simulation;Gel effect
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发布时间：2021-08-24 - 摘要：The intermediate product of the pyrolysis process of polydimethylsilane（PDMS）,liquid polysilane（LPS）,is a mixture of low molecular weight silanes with different structure and reaction activity.The diversity of the reaction activity among the components leads to the different reaction degree of rearrangement and polycondensation,and it results in a low synthesis yield of polycarbosilanes（PCSs）.In this work,PCSs were synthesized from LPS,which was obtained by thermal decomposition of PDMS,with an reaction additive——benzoyl peroxide（BPO） as the initiator.By using this method the yield of PCS from LPS has an increase of 20%～25%.The reaction process was traced by FTIR and GPC.The structure,composition and properties of PCS were investigated by EA,（）1H-NMR,（）13C-NMR,TG-DTA and XRD.The reaction mechanism of LPS with BPO was studied in detail.The results showed that,with raising the mass ratio of BPO to LPS and the reaction time,the weight average molecular weight（Mw） and softening point of PCSs increased.The Si—H bond content of PCSs increased with temperature in the range below 440℃ and decreased over 440℃,while the Si—CH2 bond content of PCSs increased with temperature rising.The conversion process included initially the formation of PCS by thermal decomposition of LPS and also then the increase in molecular weight by condensation among the PCS molecules.And BPO can effectively catalyze the thermal decomposition and rearrangement of Si—Si bonds in LPS when heated,and also the formation of Si—CH2—Si from Si radical and Si—CH2 radicals.The molecular chain of PCS grows up,and the yield of PCS increases accordingly.Some phenyl and benzoyloxy groups are introduced into PCS molecules;it results in a little increase of carbon and oxygen contents of PCS.However the excessive BPO leads to excess crosslinking of PCS and makes the reaction uncontrollable.The proper softening point of the achieved PCS can be tailored by controlling the mass ration of BPO to LPS about 0.02,the reacting temperature（about 450℃） and reacting time（3～4 h）,and a high synthesis yield of about 67% can be obtained,which is much higher than that of PCS synthesized by existed method.In addition,the carbon content of PCS increases by about 4%,and the oxygen content of PCS increases by about 0.4%.However they have little effect on the PCS’s ceramic yield and pyrolysis conversion properties.When the softening points of PCS is in the range of 210～220℃,the ceramic yield is over 70%.It is proved by the TG-DTA and XRD analyses of the pyrolsis products of PCS.关键词：Polycarbosilane;Liquid polysilane;SiC;Benzoyl peroxide
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发布时间：2021-08-24 - 摘要：Study,streaming potential measurements were use to investigate the effect of surface electric properties of composite nanofiltration（NF） membranes on their separation performance.NF membranes have been prepared by different functional materials.The different charged functional groups will give different hydrolyzed properties in the same electrolyte solution,and the charged properties will be different too.The streaming potential measurements can be used to characterize the surface charged properties of membranes.The experiments were carried out with plate NF membranes.When an electrolyte solution is forced to flow through a membrane pore by means of a hydraulic pressure,a streaming potential is generated across the flow path.The membranes were prepared using（poly[2-（N,N-dimethyl） amino）ethyl methacrylate]（PDM） and poly[2-（N,N-dimetbyl amino） ethyl acrylate]（PDA） as functional layers,respectively.Several electrolyte solutions were used as measured media such as 0.005 mol/L MgSO4,MgCl2 and Na2SO4 solutions.Effects of cross-linking time of the functional layer of the composite NF membrane and molecular structure of monomers on the surface electric performance of NF membranes were studied. Relations of selective rejection performance with surface electric performances of NF membrane to different inorganic salts were investigated.Streaming potential（ΔE）,zeta potential（ζ） and the surface charge density（σd） at the exterior surface of NF membrane were obtained by the streaming potential measurement.The results show that the variations in these three eletric parameters are in accordance with the variations in the cross-linking time of the functional layer and with the variations in the rejection of the NF membrane to inorganic salts.When the cross-linking time is 45 s,all of the absolute values of these electric parameters take their maximum values.The electric parameters correlated well with the rejection of NF membrane to inorganic salts. The absolute value of zeta potential（|ζ|） of the composite NF membrane increased as Na2SO4 >MgSO4>MgCl2,and the flux and rejection show the same increasing.The absolute values of the surface electric data of the NF membrane obtained by PDM with methyl groups on the main chains are smaller than the NF membrane obtained by PDA without methyl groups.The atomic force microscopy（AFM） was chosen for morphological characterization of the surface of NF membranes.AFM measurements reveal that the chemical structures of the monomers strongly affect the surface morphology.The surface roughness of the PDM NF membrane is higher than that of the PDA NF membrane.The increase in the number of methyl groups on the main chains of monomers results in the membrane morphology,which affects the surface eclectic properties of the membrane.The AFM measurements conform the streaming potential data.Therefore,the streaming potential method is a useful tool to be used in studies of rejection mechanism and studies of functional structure of composite NF membranes.关键词：Nanofiltration membrane;Charged membrane;Streaming potential;Zeta potential;Surface charge densities
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发布时间：2021-08-24 - 摘要：The nanocomposites of hydrogenated nitrile rubber（HNBR）/poly（magnesium methacrylate）（PMgMA） were prepared by compounding and in situ polymerizing in the curing process by using different contents of MgMA as a reinforcing agent and dicumyl peroxide（DCP） as a curing agent.The structure,morphology and properties of the nanocomposites were investigated by means of XRD,FTIR,（）13C-NMR,SEM,TEM,DMA and crosslinking density analysis,and the interrelated modification mechanism was expounded.The results showed that the diameter of MgMA particles decreased obviously during the mixing,and a part of MgMA monomers graft-copolymerized onto HNBR chains while MgMA monomers in situ polymerized during vulcanization,and hence grafted interpenetrating polymer networks were formed（grafted IPN）.With increasing MgMA content the stress at 100% elongation,tensile strength,elongation at break,tear strength and heat air ageing properties of the nanocomposites were improved.The tensile strength and elongation at break of the nanocomposites with 30 phr MgMA contents are 38.5 MPa and 545%,respectively,at the same time they exhibit the excellent air-oven ageing properties.MgMA can increase markedly the storage modulus（E′） and decrease the loss factor（tanδ）.When the contents of MgMA were increased,the total crosslinking density and ionic crosslinking density of HNBR nanocomposites were increased,but covalent bonds crosslinking density were decreased,indicating the ionic crosslinking bonds exert a significant effect on the mechanical properties of HNBR nanocomposites.HNBR having 36% acrylonitrile content was provided by Zeon Chemical,Japan.The Mooney viscosity ML（1+4） 100℃ of the rubber is 135.The compounds were mixed on a two-roll mill（friction ratio 1∶1.12） below 60℃ for 15 min.Accelerating agent,anti-ageing agent,activating agent,and MgMA were added into HNBR rubber matrix in sequence.The curing agent DCP was added at last.The optimum cure time（tc=90 min） was determined by U-CAN UR-2030 vulcameter,Taiwan.The samples for tensile testing were then prepared in an electrically heated press at 178℃ for tc=90 min.Tensile tests were conducted following ISO standard 37-2005 at room temperature.The structure and morphology of HNBR/PMgMA nanocomposites were characterized by FTIR,XRD,（）13C-NMR,SEM,TEM and DMA.The crosslinking density analysis was based on Flory-Rehner equation.Magnesium methacrylate is a very effective reinforcing agent for hydrogenated nitrile rubber.The MgMA monomer in situ polymerized and graft-copolymerized onto HNBR chains during vulcanization,and hence formed the grafted interpenetrating polymer networks（grafted IPN）.The ionic crosslinking bonds have important effects on the properties of nanocomposites.The excellent general mechanical and ageing properties of HNBR/PMgMA nanocomposites can be achieved when the content of MgMA is between 20 and 40 phr.关键词：Hydrogenated nitrile rubber;Magnesium methacrylate;Nanocomposites;Structure;Morphology;Property
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发布时间：2021-08-24 - 摘要：Thermo-sensitive polymers have gained great interest in recent years due to the unique features facilitating their applications in a variety of areas,such as controlled drug release,biotechnology,separation,etc.They exhibit fast,reversible volume changes around their lower critical solution temperature (LCST).More recently,much attention has been paid to the preparation of ionic thermo-sensitive polymers because polyions are readily adsorbed on the surfaces with opposite charges and polycations have been proposed as novel non-viral vectors for gene delivery.It is well known that PVA is a cost-effective,low toxic and biocompatible polymer.Not only applied to industrial products such as fibers,coatings and films,PVA has also been utilized in biomedical applications,such as artificial kidney,pancreas,etc.In this paper,glycidyltrimethylammonium chloride(GTMAC) and acetaldehyde were selected to modify(poly(vinyl) alcohol)(PVA) in an attempt to render PVA thermo-sensitive and cationic characters,where the GTMAC introduces cationic groups whereas acetaldehyde provides hydrophobic ethyl groups.The structure of modified PVA(CAPVA) was characterized by elemental analysis,surface charge density and NMR.And the thermo-sensitivity or LCST was revealed by using a turbidimeter.It is found that CAPVA is water-soluble and generates clear aqueous solution below LCST.As the temperature rises above LCST,the chains are hydrophobically associated or aggregated,leading to phase separation of the formation of CAPVA agglomerates.The LCST of CAPVA was influenced by the amount of cationic groups,the degree of acetalysis and the concentration of NaCl in solution.The LCST of CAPVA containing more cationic groups and less acetal rings was relatively high(up to 75℃),which was lowered gradually with the increase of NaCl concenrtration.The LCST of CAPVA can be tailored or adjusted via controlling the densities of cationic groups and acetal rings as well as the electrolyte concentration.关键词：Poly(vinyl alcohol);Cationization;Acetalyzation;LCST;Thermo-sensitive
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发布时间：2021-08-24 - 摘要：An amphiphilic comb-like polysiloxane(ACPS) containing polyether side chains is presented as the modification reagent in preparation of hydrophilic porous poly(vinylidene fluoride)(PVDF) membrane via phase inversion process.The effects of blending ACPS on the morphology,crystallinity,mechanical properties,chemistry structure,hydrohilicity and filtration performance of porous PVDF membranes as well as the stability of ACPS in phase inversion process were investigated.Basing on the membrane forming kinetics displayed from measuring the light intensity transmitted through the membrane,it was found that the addition of ACPS would lead the delayed demixing between casting solution and coagulating water during the phase inversion process.The instantaneous demixing resulted in the formation of membranes with "fingerlike" macrovoids in the sublayer,whereas the delayed demixing yieded membrane structure containing a "spongelike" sublayer.And thus,the solidified PVDF membrane with larger pore size was obtained with increasing the content of PVDF in casting solutions.Furthermore,the introduction of ACPS into the membrane system increased the PVDF crystallineity because the delayed demixing permitted a longer crystallization time in membrane formation.Surface and bulk chemical compositions of blend membranes were measured respectively to study the reservation and the enrichment of ACPS molecules in the membrane formation proces.It was revealed that the O/F ratio of membrane bulkwas almost the same as that of the corresponding casting solution,which obviously indicated the higher reservation of ACPS inmembrane formation proces.The fact that the O/F ratio in membrane surface layer was much higher than that in membrane bulk proved the enrichment of ACPS on surface.The reason for such surface enrichments could be explained as follows.In phase inversion process,the ultra-hydrophilic poly(ethylene oxide)side chains in ACPS tended to moving out of the membrane and disslving into the coagulation bath.However,the ACPS molecule as a whole strongly entwisted with PVDF chains is not able to dissolve into the coagulation bath.As a result,the ACPS molecules enrich in the final surface layer,and the hydroiphilic poly(ethylene oxide)side chains stretch toward the outside of the membrane surface.In fact,such enrichment also occurred in wall surface of pores inside the membranes.via Supposing a schematic model,this explanation was clearly illustrated.The enrichment of ACPS with PEO side chain stretching trends endows the membrane with excellent hydrophilicity both for membrane surface and wall of pores inside membrane,which was fully proved by measurements of water contact angle.As the ACPS molecules were greatly entwisted by PVDF chains,the ACPS could be reserved in membranes stably and thus result in the reliable hydrophilic stability for PVDF membranes.Such stability is very important and greatly expected while the filtration performance in practical application of final PVDF membrane is considered.In this work,this stability was also approved clearly through continous shake test(in 60℃ water) simulating the application process.For prepared ACPS/PVDF blend membranes without further hydrophilication treatment(e.g.coated by glycerol,ethanol or other surfactant),the water flux was relative large while the retention property was controlled properly.Form the observed results it is concluded that the ACPS should be contributed to the potenial candidate materials for high performance filtration membranes.
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发布时间：2021-08-24 - 摘要：Superhydrophobic surfaces are currently a subject of great interest and enthusiastic study because of their various important applications.In this paper,the relationships between contact angle,surface roughness and surface morphology were discussed to explore a simple procedure for preparing a superhydrophobic aqueous coating with tunable roughness surface.Transparent hydrophobic films with fluorine gradient distribution have been prepared from methacrylate copolymers modified with fluoroacrylate and siloxane(γ-methacryloxypropyltriisopropoxysilane) in emulsion polymerization.The fluorine gradient distribution resulted from fluorine self-assembled was examined by X-ray photoelectron spectroscopy analysis.The strawberry-like silica particles are obtained by utilizing the graft of different size silica particles modified with epoxy and amine functional groups,respectively.This makes the film form a composite interface with irregular binary structures and a hierarchical roughness to have high air-trapped ratio.The superhydrophobic surface was obtained by making use of silica particles to increase roughness and fluorocopolymer to provide low surface energy.By comparing the difference of water contact angles on the film surfaces between the admixture of fluoroemulsion with the sole diameter silica and that with composite silica particles,it was shown that the large roughness factor is not necessary while the high air-trapped ratio is indispensable.Although the composite silica particles play a vital role in governing the surface wettability,it is necessary to combine with a low surface energy to make a surface superhydrophobic.The composite surface turns from hydrophilic to superhydrophobic only when there is a proper cooperation with the fluorocopolymer having low surface energy,and the water contact angle will decrease when the mass ratio of emulsion to silica exceeds unity because of the filling of interspace on the film surface.The largest contact angle for water on the surface of hybrid film is about(174.2±2)° and the contact angle hysteresis is close to 0°.关键词：Microstructure;Gradient distribution;Emulsion;Silica particles;Superhydrophobicity
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发布时间：2021-08-24
Research Article
- 摘要：The electron affinities（EA） of the vinyl monomers with different substituents were used to determine the anionic polymerization activities of the vinyl monomers.To obtain the theoretical EA data of the vinyl monomers,the Gaussian 03 program based on density functional theory was employed.The geometry of the monomers with different substituents was first optimized by a B3LYP method with 6-31G（d） basis sets,then the electron affinities were calculated at the level of（B3LYP/6-311++G（3df,2p）.）It is suggested that the method used to calculate the molecular electron affinity is reliable according to the comparison between the predicted and the experimental EA values.The Mulliken charges of（C）（C） double bonds in different monomers is helpful to determine the reactive sites of the anionic polymerization.The monomers with EA values less than-20 kJ·mol-1 are mainly conjugated alkenes without polarity,which only react with strong nucleophilic initiators.The EA vaules of the monomers with a relatively strong electron-withdrawing substituent are generally in the ranges of-20～60 kJ·mol-1,which can be polymerized with the weak nucleophilic.While the EA values of the monomers with two strong electron-withdrawing substituents are generally more than 60 kJ·mol-1,and the corresponding monomers can react with very mild nucleophiles.Therefore,the EA values of the monomers with different substituents could be used to determine the anionic polymerization activities of the monomers.This conclusion was further validated according to the comparison with the Q-e and σ values.关键词：Anionic polymerization;Monomer;Electronic affinity;Reaction activity;Density functional theory
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发布时间：2021-08-24 - 摘要：Spindly BaWO4 crystals were synthesized by using a high molecular weight N-containing heterocyclic homopolymer,poly4-vinylpyridine（P4VP）,as a template.The well-defined shape of BaWO4 crystals was characterized with scanning electron microscopy,transmission electron microscopy and X-ray diffraction.The size and shape of the spindly BaWO4 crystals can be controlled through adjusting the pH value and the polymer concentration of the solution.The favorite spindly BaWO4 crystals can be obtained at an appropriate polymer concentration.Spindly BaWO4 crystals with various sizes were observed at low concentration of P4VP（<0.1 g/L）.When the concentration of P4VP was larger than 1 g/L,the dimensions of the spindles were more uniform and smaller.Very uniform BaWO4 crystals with length of 2.5 μm were obtained at P4VP concentration of 10 g/L.The reactant concentration,i.e.the concentration of Ba2+ and WO2-4,played an important role in the morphological control of the BaWO4 crystals.At lower Ba2+ concentrations（0.02 mmol/L）,only clusters without the spindly appearance were found.Spindly BaWO4 crystals were obtained as the concentration of Ba2+ was increased to 2 mmol/L.Further increasing Ba2+ concentration to 20 mmol/L seriously distorted spindly BaWO4 crystals formed.The pH value also affects the formation of BaWO4 crystals.The increase of pH value promoted the formation of more uniform spindly crystals.Distorted BaWO4 nanoparticles were obtained at lower pH values（< 4）.Spindly crystals were obtained as the pH value increased to 6.5.More uniform small crystals were obtained when the pH value was increased to 8.The formation mechanism of the spindly BaWO4 crystals was suggested according to the experimental results.We suggested that at appropriate conditions(such as pH range,concentration of Ba2+ and P4VP),the Ba2+ should react with most suspended pyridyl to form BaWO4 nanoparticles of various sizes at first,and then the residual pyridyl suspended on the main chain should react with the Ba2+ in solution further to induce the orderly growth and aggregation of nanosized crystals,and spindly BaWO4 crystals form at last.关键词：BaWO4;Scheelite structure;Crystal growth;Poly4-vinylpyridine;Modifier
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发布时间：2021-08-24 - 摘要：Poly（aryl ether ether ketone ketone）s as outstanding polymer have excellent thermal stability,resistance to creep and so on.But their high melting points and low solubility in common organic solvents limited their applications.One of the modifications is introducing novel monomer to backbone.In this paper,a series of high molecular weight poly（aryl ether sulfone ethe retone ketoneco-ary ether ketone）s containing mono-ortho-methyls were obtained by low temperature solution polycondensation,taking 4,4′-bis（2-methylphenoxy）diphenylsulfone（o-MeDPODPS）as the third monomer,which aimed to introduce methyl pendant into the main chain to decrease melting temperature.The resulting copolymers’ ηinh was in the range of 0.75～1.36 dL/g,and they were characterized by FT-IR,WAXD,DSC results and TG.The DSC results revealed that the glass transition temperature of the copolymers increased with increasing the molar ratio of o-MeDPODPS,while their melting points and crystallinity decreased.The same phenomenon occurred in the 5% weight loss temperatures of the copolymers,which could be attributed to the decomposability of methyl pendant.They also show good resistance to common organic solvents in the solubility test.When the molar ratio of o-MeDPODPS is 30%,the Tg of the copolymer is 9℃ higher in comparison to PEEKK,while the Tm is 44℃ lower.
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发布时间：2021-08-24 - 摘要：High molecular weight biodegradable poly（ether ester）,poly（p-dioxanone）（PPDO）,has been prepared by chain-extending from its prepolymer using hexamethylene diisocyanate（HDI） as a chain extender.The ring-opening polymerization of p-dioxanone（PDO） using stannous octoate（SnOct2） as a catalyst was conducted at 125℃ for 3 h,and then a certain amount of HDI was added into the reactive system to react with the resulting PPDO prepolymer for an additional 30 min.The effect of the weight ratio of HDI to PPDO on the molecular weight of the chain-extended PPDO has been studied,and the results show that when the ratio is 0.78 wt%,higher molecular weight PPDO can be obtained,demonstrating that HDI is an effective extender for PPDO.The thermal degradation behaviors of PPDO and chain-extended polymer（PPDO-HDI） in air have been investigated by TG.The results show that the thermal stability of PPDO-HDI is higher than that of PPDO.Differntial scanning calorimetry（DSC） and wide angle X-ray diffractometry（WXRD） have been utilized to investigate the crystallization behavior of PPDO-HDI and PPDO.There exists no obvious difference between the crystal structures of PPDO-HDI and PPDO,however,the crystallinity of PPDO-HDI decreases to 33% from 60% of PPDO;the melting point of PPDO-HDI decreases a little and its glass transition temperature increases compared with those of PPDO.Moreover,the tensile strength and the elongation at break of PPDO-HDI are 36 MPa and 464%,respectively,almost the same as those of PPDO.关键词：(Poly(p-dioxanone);) Hexamethylene diisocyanate;Chain-extension;Thermal stability;Crystallization;Tensile property
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发布时间：2021-08-24
Research Bulletin
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