最新刊期
卷 ， 期 5 ， 2007
- 摘要：Optimal conditions for preparation of low molecular weight chitosan with sonolysis were described.The influence of sonolysis conditions and the molecular parameters of initial chitosan on the degradation rate and degradation rate constant was investigated in detail.Weight-average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of samples were measured by gel permeation chromatography.The structure of degraded chitosan was characterized by Fourier transform infrared spectroscopy and X-ray diffraction.For a given sonolysis time,the decrease in molecular weight has been found to be the greatest at the lowest reaction temperature and lowest chitosan concentration.Molecular weight of samples decreased exponentially with increasing sonication time at early stages.The action mode of ultrasound on the splitting of molecular chains of chitosan was discussed.The degree of deacetylation of the main hydrolysis products almost unchanged compared with the initial chitosan.The decrease of molecular weight led to transformation of crystal structure,but the chemical structures of residues were not modified.Ultrasonic treatment on chitosan is an alternative,safe method to prepare different molecular weight chitosan which is more suitable for biomedical and food applications.
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发布时间：2021-03-19 - 摘要：Nylon-6/ABS blends compatibilized with styrene-maleic anhydride copolymer (SMA) were prepared in a corotating twin-screw extruder.A study on compatibility between Nylon-6 and ABS using SMA as compatibilizer was conducted through observation of TEM and SEM as well as FTIR analysis.The relationship between morphology of Nylon-6/ABS/SMA blends and mechanical properties was also discussed.The poor compatibility of the blends prepared by pure Nylon-6 and ABS has been found.The boundary between the phase domains of Nylon-6 and ABS appears sharp and clear,and the dispersed phase tends to congregate.The smooth fracture surfaces indicate there exists a brittle behavior for Nylon-6/ABS blends.In case of adding SMA,the compatibility of Nylon-6 and ABS is improved remarkably.Moreover,results reveal that the morphology of blends changes from dual-continuous phase with interlocking structure into “sea-island" structure,depending on the amount of SMA added.It is noted that an improved interfacial adhesion,reduction in the particle size of dispersed phase and more uniform sizes could be achieved in the blends containing SMA.
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发布时间：2021-03-19 - 摘要：An optical active triblock copolymer poly(N-methacryloyl-L-leucine methyl ester)-b-polysulfone-b-poly-(N-methacryloyl-L-leucine methey ester) (PMALM-b-PSF-b-PMALM) with predetermined structure and narrow molecular weight distribution was synthesized via atom transfer radical polymerization (ATRP) using polysulfone macroinitiator and CuBr/Me6TREN complex system.The structure was verified by 1H-NMR,GPC and end group titration techniques.DSC,thermogravimetry analysis (TGA) and circular dichroism (CD) were used to study the thermal and optical properties.The mole ratio of PMALM block to PSF block calculated from TGA has a good agreement with the result calculated from 1H-NMR.Both a reversion and an increase of the absolute value of specific rotation in the transformation from MALM to PMALM-b-PSF-b-PMALM were observed,which were probably caused by some kind of stereostructure of the main chain formed during the polymerization due to the intermolecular hydrogen-bonding.The random conformation of PMALM blocks was verified by CD spectra and the linear relationship between the specific rotation and the polarity of CH3OH/CCl4 mixed solvent.
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发布时间：2021-03-19 - 摘要：Surface-macroporous polystyrene with sub-micrometer (250～400 nm) pores and a surface thickness of 10 μm has been synthesized using a maleic anhydride-alt-vinyl acetate copolymer microspheres as template,followed by removal of the template with water,ethanol or acetone.The surface features of the samples were investigated by scanning electron microscopy (SEM).The SEM micrographs indicate that macroporous PS can be prepared in each case,with use of water as the template's solvent having the smallest adverse effect on the polymer.The functional groups present on the surface of pores after the template was dissolved are different in each case and have been identified by FTIR,dissolution of template in water gives rise to carboxyl groups,dissolution of template in ethanol gives rise to ester groups whilst dissolution of template in acetone gives acid anhydride groups.The rate of template dissolving is fastest in acetone and slowest in water.
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发布时间：2021-03-19 - 摘要：A new class of polysilane polymers containing pendant silyl substituents,named trimethylsilyl-substituted polysilane (SPS),was prepared by polymer reaction of polymethylsilane and characterized by means of FT-IR,1H-NMR,29Si CP MAS-NMR,UV and GPC,respectively.This polymer is soluble in common organic solvents,and its molecular weight can be increased by crosslinking reaction.The property of pyrolysis shows that its ceramic yield is 44%,and it is a potential preceramic polymer.The conductivity of SPS can be as high as 10-6 S/cm in the range of semi-conductor after being doped with iodine due to the possibly wider σ-delocalized system caused by the silicon substituents.
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发布时间：2021-03-19 - 摘要：The end-to-end distance distribution of a grafted compact polymer chain confined between two parallels is studied by using the PERM （pruned-enriched-Rosenbluth method）algorithm.Because of the difference in different directions of confined polymer chains,in this paper we just consider the distribution function P(x) in the x-axis direction,and it can be expressed as ln［P(x)/Pm(x)］/ND-2/3=a0+a1u+a2u2+a3u3,here u=x/ND-2/3,N is the chain length,Pm(x) is the maximum value of P(x),D+1 is the distance between the two parallels.On the other hand,we calculate the Shannon entropy according to P(x),which is very sensitive to the variation of the distance of two parallels,and it can be used to describe the restriction of the polymer chain.With a given chain length N,the Shannon entropy of the distribution P(x) decreases rapidly first and then tends to a fixed value with increasing D,by which we can find a transition point Dc.When DDc the Shannon entropy tends to a constant,and at the same time the restriction of polymer chain performed by the two parallels can be ignored.We also find that the relationship between Dc and N as Dc-Nλ,here λ=0.543.
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发布时间：2021-03-19 - 摘要：The effect of pH value on the electrostatic layer-by-layer selfassembly and the photoresponsive behavior of on azo polyelectrolyte Poly{2-［4-(4′-ethoxyphenylazo)phenoxy］ethyl acrylate-co-acrylic acid} (PEAPE). Results show that in the studied pH value range,the lower the pH value,the higher is the UV-Vis absorbance and larger is the thickness of the multilayer films.FTIR studies indicate that the azo polyelectrolyte exhibits a different ionization degree in the solutions with different pH values.The higher absorbance and larger thickness of the layer-by-layer films can be attributed to the low ionization degree and the shrinkage conformation of PEAPE in solutions with the low pH value. FTIR analysis also confirms that the driving force for layer-by-layer self-assembly of PEAPE and poly(diallydimethyl ammoniumchloride) is the electrostatic interaction.
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发布时间：2021-03-19 - 摘要：A novel coupling agent,3-hexanoylthio-1-propyltriethoxysilane(HXT),was synthesized through the reaction of 3-triethoxysiyl-1-propanethiol and hexanoyl chloride.HXT or bis-(triethoxysilylpropyl)disulfide (TESPD) as coupling agent were incorporated into solution polymerized styrene-butadiene rubber(SSBR)/silica(SiO2) compounds.Dynamic rheological properties of the compounds were investigated by using an advanced rheomitric expended system (ARES).It is found incorporation of silane coupling agent into SSBR/SiO2 compounds improved the elastic properties and wakened the Payne effect due to the surface modification of SiO2 particles and the improved dispersion of the particles in the SSBR matrix.Compared with TESPD,HXT provides rubber compounds with higher critical strain value of Payne effect and lower storage modulus.In this aspect,HXT performs better than TESPD.This might be attributed to the combined effects of better rubber-filler interaction and better filler dispersion which are obtained when TESPD is replaced with HXT.
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发布时间：2021-03-19 - 摘要：Polylactic acid was synthesized from commercial available cheap aqueous lactic acid(85 wt%～90 wt%) using succinic anhydride and SnCl2·2H2O as catalyst in the absence of organic solvents.As a result,polylactic acid with a molecular weight of 6×104 was prepared in 10 h.The effect of the amount of catalyst used,reaction temperature,and reaction time on the polymerization were investigated in detail.The amount of catalyst is the main factor that effecting the polymerization.The yields and molecular weights of the PLA obtained by succinic anhydride increase with the amount of succinic anhydride used in the range of 0 to 0.07 wt%.The trend is changed to decrease when the amount of the catalyst exceeds 0.07 wt%.The optimum amount of succinc anhydride is about 0.07 wt%,considering high Mw and high yield.The reaction time is another factor that effecting the polymerization.In a period of 0～10 h,the yield and molecular weight increase with the reaction time.In the longer reaction time that exceeds 10 h,the yields and molecular weights decrease with the time.The molecular weight of PLA reach a maximum after the reaction has been carried out for about 10 h.Polylactic acid obtained by succinic anhydride and SnCl2·2H2O was characterized by IR and NMR.This is a new catalytic system for the direct polymerization of the lactic acid.The catalyst is commercially available and used as received without further treatment.The monomer we used is cheap and renewable aqueous lactic acid.The new procedure is much simple,cheap and environmentally benign compared to those of the reported ones.This kind of polymer might be useful in biomedical applications.
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发布时间：2021-03-19 - 摘要：The organoclay(TMT)-natural rubber (NR) nanocomposites were prepared by mixing intercalation method.The structure of organoclay was analyzed by X-ray diffraction (XRD) and FTIR.The heaf release rate and the smoke production of the TMT/NR nanocomposites are lower than those of montmorillonite/NR composites.The experimental flammability and mass loss curve were analyzed,and the flame retardant mechanism of TMT/NR was discussed.The results indicate that TMT/NR nanocomposites is a flame retardant and environmentally friend system.
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发布时间：2021-03-19 - 摘要：Polyaniline (PANI) nanofibers with a higher conductivity (10-2～10-1 S/cm) were synthesized by “template-free” method in the presence of ferric chloride as oxidant at dopant-free via interfacial polymerization of aniline (An).Compared with previous interfacial polymerization,this method is more simple and cheap because ferric chloride acting as both oxidant and dopant at the same time,resulting in omitting external dopant.Moreover,the resulting nanofibers show thinner diameter and higher crystallinity than those of the nanofibers oxidized by APS which perhaps due to its low redox potential of FeCl3.It is also found that the morphology and conductivity of the nanofibers at room-temperature change with the increase of ［FeCl3］/［An］ ratios.The nanofibers were characterized by FTIR and UV-Visible absorption spectra,and the results indicated that they were identical to the emeraldine salt state of PANI.
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发布时间：2021-03-19 - 摘要：Shear-induced crystallization behavior of isotactic polypropylene (iPP) was investigated using a rotational rheometry covering a shear rate range of 1.2×10-4～1 s-1 and temperatures between 135℃ and 145℃.As the specimen was sheared at a constant rate,the viscosity and normal force were constant at first,then started to increase sharply after a certain time.At higher shear rates the transition of the normal force occurred considerably earlier than that of the viscosity,and at medium shear rates the two transition times were coincident.However at extremely low shear rates the data of normal force became noisy and only the data of viscosity was reliable.It was suggested that the earlier time in transitions for the normal force and viscosity was used to define an onset time （ton）which characterized the crystallization process.Furthermore,it is proposed that the plot of ton versus shear rate can be converted into a temperature-invariant curve by dividing the y axis by quiescent onset time ton,q and multiplying the x axis by ton,q.
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发布时间：2021-03-19 - 摘要：A one step metohd approach for synthesis of polydimethylsiloxane (PDMS)-containing macroazoinitiator (MAI) was developed by direct polycondensation of hydroxyalkyl-terminated PDMS with 4,4′-azobis-4-cyanopentanoic acid (ACPA) under mild conditions by the use of dicyclohexylcarbodiimide (DCC) as the activating agent and 4-(dimethylamino) pyridinium-p-toluenesulfonate (DPTS) as the catalyst.The resulted MAI was then used as an initiator for polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) macro-monomers,and amphiphilic PDMS-PEG block copolymers were successfully synthesized.Results from the characterization of block copolymers showed that the resulted MAI had very high initiation efficiency and the block copolymers had microphase-separated structure.
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发布时间：2021-03-19 - 摘要：A novel electroresponse intelligent hydrogel of crosslinked polyvinyl sulfate potassium (PVSK)was prepared by the sulfating reaction of crosslinked polyvinyalcohol,and the effect of the ionic strength and pH on the swelling ratio at equilibrium,mechanical properties and electromechanochemical behavior of the PVSK hydrogel were studied.The experimental results indicated that the swelling ratios at equilibrium of PVSK hydrogels decreased with increasing the ionic strength of NaCl solutions and were almost invariable in the pH range of 2.39～10.83.The PVSK hydrogels swollen in NaCl solutions of different pH and ionic strength presented excellent mechanical properties.The PVSK hydrogel bended toward the cathode under non-contact D.C.electric field in NaCl aqueous solutions,the bending speed and bending strain of the PVSK hydrogel increased with increasing the applied voltage and were almost invariable in the pH range of 2.08～10.53.The electroresponsive behavior of the PVSK hydrogel was also affected by the electrolyte concentration of the external NaCl solution,and there was a critical ionic strength of 0.1 at which its bending speed and equilibrium strain reached their maximum values.Under a cyclically varying electric field the hydrogel exhibited a good reversible electromechanochemical behavior.
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发布时间：2021-03-19 - 摘要：Hydrophobically associated polyacrylamide was synthesized by copolymerization of acrylamide (AM) and a surface-active monomer,sodium 2-acrylamidotetradecane sulfonate (NaAMC14S),in an aqueous homogenous phase system.Based on the exploited copolymerization mechanism and by controlling the concentration of NaAMC14S above its critical micelle concentration,copolymers NaAMC14S/AM with microblocks structure were obtained.By varying the feed ratio of NaAMC14S and AM,the added amount of electrolyte NaCl and the amount of initiator,respectively,thre series of copolymers NaAMC14S/AM with various microstructures were prepared.The dependences of hydrophobic associating properties of the copolymers on the microstructures were studied by the fluorescence probe method and the apparent viscosity measurement method,and the effects of the content and length of the hydrophobic blocks and the molecular weight of the copolymers were explored thoroughly.The experimental results show that the hydrophobic associating properties of copolymers NaAMC14S/AM is strengthened with the increase of the content and length of the hydrophobic blocks and is enhanced with the increase of the molecular weight of the copolymers.
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发布时间：2021-03-19 - 摘要：Microcapsules with dodecanol (C12OH) encapsulated were prepared through complex coacervation by adding gelatin (GE) solution to an acacia gum (AG) solution and through GE simple coacervation by adding sodium sulfate solution to GE solution,both in presence of C12OH.C12OH was chosen for the core material because it does constitute a real component in sex pheromones of numerous insects.In a first step,Zeta potential and light transmittance in the two coacervation processes were followed in order to determine the optimum ratio of AG and GE in complex coacervation and the best amount of sodium sulfate in simple coacervation.It was observed that maximum yield was achieved for complex coacervation with AG/GE weight ratio at unity,and for simple coacervation when 30 mL of 20% sodium sulfate was added to 40 mL of 6% GE solution.When the wall material concentration was equal to or higher than 3%,the size of the microcapsules from complex coacervation was larger than that prepared through simple coacervation.Nevertheless,simple coacervation led to capsules with much narrower size distribution.C12OH encapsulation rates in simple coacervation were significantly lower compared with those in complex coacervation at equal wall material concentration,leading therefore to a lower C12OH loading in simple coacervation.To investigate C12OH release from the capsules,samples were placed into an incubator with constant temperature (30℃) and relative humidity (50% RH),and taken out for C12OH examination by gas chromatography and by weighing the samples.It was found that all samples from simple coacervation reached their final release in less than one week,no difference was observed for samples prepared with different wall material concentration; whereas microcapsules from complex coacervation manifested a three_step_release profile,i.e.a quick start followed by a constant plateau region and terminated by a release increase till completion.Results also revealed that capsules prepared with higher wall material concentration had a higher release rates.The capsules prepared with 5% solutions of AG and GE lost their C12OH within 2 weeks; lowering wall material concentration effectively reduced C12OH release rate and extended C12OH constant release period.This work indicates that release of C12OH can be well controlled through capsule structure designing.This is of great importance for our on_going study on controlled release of authentic insect semiochemicals.
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发布时间：2021-03-19
Research Article
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