最新刊期
卷 ， 期 1 ， 2008
- 摘要：A three-component negative-type photosensitive branched polyamide based on an endmodified polyamide b,4,4′-methylenebis［2,6-bis(hydroxymethyl)phenol］(MBHP) as a cross-linker and a photoacid generator(5-propylulfonyloxyimino-5H-thiophen-2-ylidene)-2-(methylphenyl)acetonitrile(PTMA) has been developed.The polymer b was prepared from a branched polyamide a having degree of branching of 0.36 and cinnamyl chloride,while polymer a was sythesized from an ABB' type monomer,4-(2,4-diaminophenoxy)benzoic acid 3 in the presence of triphenyl phosphite/pyridine (TPP/Py) as a condensing agent.3 was prepared in three steps starting from the displacement of 4-hydroxybenzoic acid methyl ester with 2,4-dinitrofluorobenzene in the presence of potassium carbonate,the nitro groups of 4-(2,4-dinitrophenoxy) benzoic acid methyl ester 1 were reduced to amino groups by hydrogenation in ethyl acetate,and subsequent alkaline hydrolysis of the resulting 4-(2,4-diaminophenoxy) benzoic acid methyl ester 2.In order to avoid the effect of polymer a with amino groups on the subsequent reaction (light crosslinking) of the branched polymer,the end-modification of the amino groups was carried out by using cinnamyl chloride 5.Prior to the endmodification of polymers,the reaction of aniline 4 and 5 for determining whether the desired model compound 6 was formed in quantitative yield to constitute a polymer-forming reaction and to confirm the structure of polymers was studied.The end-modification reactions of polymer b was performed based on the reaction conditions of the model compound above described.Followed by end-modified polymer b with cinnamoyl was successfully prepared with cinnamyl chloride.The monomer 3,model compound 6 and the polymers were characterized by 1H-NMR,The average molecular weights of the polymers were determined by gel permeation chromatography(GPC).The thermal stability of the polymers was measured by thermogravimetric analysis (TGA) under a nitrogen atmosphere.The findings show that the monomer 3 and model compound 6 were successfully synthesized.Degree of branching of branched polyamide a was 0.36,caculationed from 1H-NMR,according to the definition of degree of branching given by Frey.Inherent viscosities (ηinh),weight-average molecular weight (Mw)and polydispersity（Mw/Mn）of polymer a and b were 0.39 dL/g,0.64 dL/g,7.49×104 and 1.31×105,1.88 and 3.5, respectively.Thermogravimetric analysis (TGA) was used to measure the thermal stability of the polymers,5% weight loss temperature (Td5) of polymer a was observed at 356℃,which is higher than that of polymer b (356℃).The difference in TGA traces may be caused by the terminal cinnamoyl groups.Almost resulting polyamide a and end-capping polyamide b showed excellent solubility and readily dissolved in various solvents such as N-methyl-2-pyrrolidinone (NMP), N,N′-dimethylacetamide (DMAc),N,N′-dimethylformamide (DMF). The photosensitive polymer containing polymer b (85 wt%),MBHP (10 wt%) and PTMA (5 wt%) showed a clear negative image featuring 40 μm line and space pattern when it was pre-baked at 100℃ for 10 min,subsequently exposed to a 436 nm light (g-line) and developed with a developer of DMF at 25℃ for 10 s,rinsed with water (H-2O),post-baked at 110℃ for 3 min.
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发布时间：2021-03-19 - 摘要：The shear stability and degradation mechanism of crosslinked polymer systems comprising of low concentration and high molecular weight partially hydrolyzed polyacrylamides （HPAM） and aluminum citrate （AlCit） were investigated by viscometry,nuclear pore membrane filtration and dynamic light scattering.The results indicated that the filtering rate in 1.2 μm nuclear pore membrane of crosslinked polymer system formed by low concentration HPAM and AlCit increased and the plugging efficiency decreased,while the shear rate became high.The shear stability of this system was not good,so its plugging efficiency was weak under shear.For crosslinked polymer systems formed by the degraded HPAM in high shear rate and AlCit,the plugging efficiency was little affected under low shear rates,but was lowered obviously in the range of high shear rate.The crosslinked polymer system formed by the degraded HPAM in high shear rate was almost not able to plug the 1.2 μm nuclear pore membrane,but was able to plug the 0.4 μm nuclear pore membrane.Low concentration HPAM which had the same concentration with the former could not plug the 0.4 μm nuclear pore membrane,but the pore membrane with a less small pore diameter after shear.The size of crosslinked polymer coils (LPC) in the crosslinked polymer system and the low concentration HPAM and high molecular weight partially hydrolyzed polyacrylamides （HPAM） coils gradually became smaller while the shear rate became high.The reason that the plugging efficiency of crosslinked polymer system after degradation decreased at high shear rate was that the size of LPC and high molecular weight partially hydrolyzed polyacrylamides （HPAM） coils became smaller because of the rupture of crosslinked polymer coils (LPC) and the partially hydrolyzed polyacrylamides （HPAM） molecules.
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发布时间：2021-03-19 - 摘要：Polydimethylsiloxane emulsions are widely used in coatings,personal care products,because of their low toxicity,high chain flexibility and low surface energy.It has various good properties,such as thermal stability,low temperature performance and lubricity.It has been applied to different areas of industry.A polydimethylsiloxane miniemulsion was prepared with sodium dodecylbenzene sulfonate (SDBS) as emulsifier,sulfuric acid or hydrochloric acid as catalyst,octamethylcyclotertrasiloxane (D4 as monomer,hexadecane (HD) as costabilizer and ultrasonication as preemulsification method.By reducing the monomer droplet size using pre_emulsifying method,and using hydrophobic substance as costabilizer to retard monomer transfer in aqueous phase,the monomer droplets become independent mini_reactors in miniemulsions.The effects of ultrasonic time,amount of catalyst and emulsifier,and temperature on kinetics of miniemulsion polymerization were investigated.Short ultrasonication time is not sufficient for obtaining the stable miniemulsion and high conversion of D
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发布时间：2021-03-19 - 摘要：The phase structure and morphology of the blends of polypropylene (PP)/polyamide (PA1010) and a partcompatibility system (PP/PA1010/PP-g-MAH) were analyzed by graph technique using scanning electron microscope (SEM) images.The structure parameters，such as the average diameter,d,average chord lengths,∫,and distance between mass centers,D,of the dispersed phase,in PP/PA1010 and PP/PA1010/PP-g-MAH blends were calculated.The morphology,as well as the relationship between the structure parameters and the compositions of the two blend systems was discussed.These results showed that the variation of structure parameters depended upon the compositions of blends.Simultaneously,the mechanical properties of the blends were measured.They depended on the compositions of the blends.For PP/PA1010 blends,the relationship between the modulus and the composition was complex.When the content of PP increased from 10% to 20%,the modulus increased and the numerical value of the modulus of the blends was greater than that of PA1010.The modulus reached a minimum when the content of PP varied from 20% to 70%.This was because a doublecontinuous phase appeared in this region.The modulus was constant and was close to that of PP when the content of PP was greater than 70%.However,when PP was the dispersed phase,the yield strength had a linear relationship with the content of PP.The yield strength decreased with the increase of the content of PP in blends.For PP/PA1010/PP-g-MAH blends,the modulus changed linearly with the variation of the content of PP because of the existence of compatibilizer.The modulus increased when the content of PP increased.The yield strength changed linearly with the content of PP in PP/PA1010/PP-g-MAH blends.The yield strength decreased with the increase of the content of PP when PP was the dispersed phase whereas the yield strength increased when PA1010 was the dispersed phase.The relationship between the mechanical properties and the structure parameters,such as the ratio of average chord lengths,∫1/∫2,was discussed.For PP/PA 1010, ∫1/∫2,showed linear relationship with the mechanical properties of the blends.Moreover,this relationship obeyed the same rule as that of the relationship between mechanical properties and the content of PP.For PP/PA1010/PP-g-MAH blends, ∫1/∫2 was also linearly related with mechanical properties.The modulus increased while the yield strength decreased with the increase of∫1/∫2.The studies on the relationship between the mechanical properties and the average diameter of thedispersed phase showed that this relationship was complex for PP/PA1010 blends.The circumstance was different when average diameter was less than 4 μm and greater than 10 μm.However,for PP/PA1010/PP-g-MAH blends,the mechanical properties were linearly related with the average diameter.Both the modulus and the yield strength decreased when the average diameter increased.The experimental results also indicated that the mechanical properties had a linear relationship with the distance of mass centre,D,for both blends.In both cases,the modulus and the yield strength decreased slowly with the increase of the average diameter.Generally speaking,the phase structure parameter has a certain relationship with the mechanical properties of the blends.
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发布时间：2021-03-19 - 摘要：RAFT polymerization is a type of psudo_living radical polymerization.In order to synthesize high pure block copolymers by RAFT polymerization,it is desirable to suppress the irreversible termination which may result in the formation of dead chains.For polymers less than 5×104 g/mol,the dead chain fraction could remain to be lower than 0.1 by reducing the initiator concentration.In the synthesis of block copolymers,the dead chains formed in the first stage are actually contaminant.Targeting to the synthesis of high pure block copolymers with high molecular weight using RAFT polymerization,we studied the copolymerization of butyl acrylate and styrene mediated by 1_phenylethyl phenyl_dithioacetate (PEPDTA) as a RAFT agent.The influences of the type of initiators (AIBN (2-2′-azobis(isobutyronitrile)),ACC(1-1′-azobis(cyclohexane_carbonitrile)),the concentrations of initiator and polymerization temperature on the copolymerization kinetics and molecular weight and its distribution were investigated.When AIBN was used,the polymerization would stop at middle monomer conversion,which limited the increase of molecular weight of the copolymer if we reduced the initiator concentration.It was found that only with the initiator (ACC) with small decomposition rate constant and high polymerization temperature,the block copolymer with high molecular weight and small fraction of dead chains (0.1) could be synthesized.The reason for these quite strict requirements is that the initiator concentration should remain far below that of the conventional radical polymerization,which is limited by the very low RAFT concentration.
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发布时间：2021-03-19 - 摘要：A series of azobenzene functionalized poly(aminoamine) dendrimers (Gn-azo(n=1～5))and the corresponding model compounds were synthesized and characterized by 1H-NMR, 13C-NMR,FTIR and elemental analysis, and the photo and H+ responsive behaviors of these dendrimers were studied through UV-Vis and H-NMR spectroscopy.It was found that the graft ratios of these azobenzene-shelled dendrimers were in the range of 70%～90%.A structural transition occurred between the third (G3-azo)and the fourth (G4-azo)generation,indicating that a relative open and loose structure of lower generation dendrimers became a dense spherical structure at higher generations.Therefore,the fourth (G4-azo)and the fifth (G5-azo)generation modified PAMAM dendrimers are ideal nano-containers that can encapsulate guest molecules.The modified dendrimers(Gn azo(n=1～5))exhibited the similar photo-responsive behaviors to azobenzene itself.Under 365 nm UV-light irradiation,the intensity of the π-π* band at 336～348 nm decreased, and the intensity of the n-π* band at 440～443 nm increased.The case was reverse under visible-light irradiation.1H-NMR results indicated that Gn-azo dendrimers could be protonized when adding trifluoroacetic acid (TFA) into the chloroform solution of Gn azo.It was also found that the protonated and nonprotonated dendrimers showed different behaviors in response to UV-light.The ratio of trans cis isomerization of the azobenzene chromophores was lower in protonated form when compared to that in non-protonated form.It might be due to that the NN group of azobenzene on the periphery was also protonized under the TFA environment.Moreover,the ratio of trans cis isomerization decreased with the generation increasing,which might be owing to the structure and size of dendrimers.The encapsulation ability of azobenzene-shelled G4 dendrimer decreased relative to the unmodified G4 dendrimer,but the release of salicylic acid was indeed slowed down because of the shielding effect of azobenzene chromophores on the periphery.More interestingly,the release of guest molecules was further slowed down with irradiating the modified dendrimers by UV-light.Under UV-light,the trans cis isomerization of the azobenzene chromophores occured,which made it more difficult for the salicylic acid to pass through the dendrimer periphery.
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发布时间：2021-03-19 - 摘要：The mechanism of the electropolymerization of aniline in 0.5 mol/L sulfuric acid was studied in detail by in situ UV-Vis spectrometry.Spectroelectrochemical experiments were done in a three electrode cell built with a quartz cuvette of 1cm path length.The work electrode was an ITO (indiumtin oxide) conductive glass perpendicular to light path,and the counter electrode was a platinum wire.An Ag/AgCl electrode with saturated KCl served as reference electrode.All potential values in the article were against to the reference.The acquired in situUV-Vis spectra showed that polyanilines could be electropolymerized at aniline concentrations 0.01,0.05 and 0.2 mol/L in sulfuric acid by cyclic voltammetry.Based on in situ UV-Vis spectra corresponding to cylic potential sweep at three different concentration of aniline above,the plots of the relationship between absorbance at 350 nm and 750 nm and elctrolysis time was made,which showed that the obvious inductive period in electropolymerization of aniline by cyclic voltammetry was seen for 0.01 mol/L aniline in 0.5 mol/L sulfuric acid water solution.In order to study how the concerntration of aniline in 0.05 mol/L sulfuric acid and the potential applied on ITO conductive glass electrodes effected the polymerization of aniline,in situUV-Vis spectra was recorded during electrolysis of solution by potentiostatic method at different concentrations of aniline in 0.5 mol/L sulfuric acid.These in situ UV-Vis spectra indicated that the polymerization of aniline occurred by electrolysis of aniline at potentials 0.8,1.0 and 1.3 V when the concentration of aniline was greater than 0.05 mol/L,however at potential 0.8 V,the polymerization of aniline did not happen in 0.01 mol/L solution of aniline.in situ UV-Vis spectra at the earlier phase of aniline electropolymerization by potentiostatic way showed that the 350 nm absorbance band appeared before the 750 nm absorbance band.This fact proposed that lower molecular weight oligomer intermediates during electrochemical polymerization of aniline might exist and that the intermediate was brought out prior to the production of polyaniline on ITO electrode.When the ITO conductive glass electrode was placed parallel to the light path,no absorbance bands were observed during electrolyzing 0.05 mol/L of aniline at potential 0.8 V,which showed that the intermediate and polymer mainly were produced on the ITO conductive glass electrode.These phenomena was not reported up to now.When the aniline concentration was 0.01 mol/L,and the potential applied on the ITO glass conductive electrode was 0.8 V,there were only an absorbance band at 350 nm in corresponding in situ UV-Vis spectra,which showed that the intermediates such as low molecular oligomers could be produced and exist on the ITO electrode,but did not lead to the formation of polyaniliane because of the low concentration of intermediates.After aniline of 0.05 mol/L in 0.5 mol/L sulfuric acid was electropolymerized by potentiostatic electrolysis at a potential 0.8 V for 70 min,the electrolysis was stopped,but in situ UV-Vis spectra were recorded continually.The red shift of absorbance band in spectra was seen,which indicated that polyaniline produced on the ITO electrode was of oxidized state and could react with aniline monomer in solution to form polyaniline at the reduced state.
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发布时间：2021-03-19 - 摘要：The liquidliquid phaseseparation (LLPS) and isothermal crystallization behavior of isotactic polypropylene/ethylenepropylene rubber blend (iPP/EPR) were investigated by using small angle laser light scattering (SALLS),differential scanning calorimetry (DSC),phase contrast microscopy (PCM) and polarized optical microscopy (POM).Results reveal that LLPS of (50/50,W/W) iPP/EPR blend happens at temperatures above the melting point of iPP,and its kinetics follows the spinodal decomposition (SD) mechanism.The apparent diffusion coefficient (Dapp) and the spinodal temperature (Ts) of the iPP/EPR samples were calculated on the basis of the CahnHilliard theory.Moreover,it is found that the Dapp increases with the increase of temperature,representing the LCST behavior of iPP/EPR.The development of phase morphologies could be obtained by quenching in liquid N2 the iPP/EPR samples subjected to annealing with different time at 200℃.On the other hand,the structure of iPP/EPR melt appears nearly homogenous at the beginning of LLPS.Furthermore,the co-continuous phases form,and the phase connectivity grows until macroscopic spherical texture generates.Both the increases of phase separation time (tps) and phase separation temperature (Tps) result in the decrease of the crystallization rate.The kinetic results indicate that the Avrami model is qualified for describing the isothermal crystallization of iPP/EPR.It is believed that the degree of phaseseparation has little effect on the crystallization kinetics and the crystallization gives priority to instantaneous nucleation and threedimensiongrowth.
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发布时间：2021-03-19 - 摘要：It is well reported that human telomeric DNA sequence［AGGG(TTAGGG)3］can form a welldefined quadruplex structure with the hydrogen bonds between guanine bases in the appearance of K+ and Na+. It was reported that the formation and stability of the structure was meaningful for both gene regulation and apoptosis. In this study,the replacement of guanine bases in this sequence with thymine,adenine and cytosine at different position was carried out respectively.Their ability to form G-quadruplex as well as the G-quadruplex stability has been studied by circular dichroism (CD) spectroscopy.All oligonucleotides were synthesized and purified by Saibaisheng company.The concentrations of the oligonucleotides,expressed in singlestrand molarity,were determined by UV absorption at 260 nm using a ‘nearestneighbor’ approximation. Circular dichroism experiments were performed on a JASCO model J810 circular dichroism spectrapolarimeter equipped with a Peltier temperature controller.All samples (10 μmol/L in 10 mmol/L trisHCl buffer containing 100 mmol/L NaCl at pH 7) were preheated to 95℃ for 5 min and slowly cooled to room temperature prior to measurements.A 1 mm path length cell was used for all measurements, and each spectrum was an average of five scans at 5℃.The Gquadruplex solutions were recorded in the 5℃ to 95℃ temperature range,using a scan rate of 0.5 K min-1 and following the variation of CD absorption at its peak around 295 nm.Analysis of the thermal curves was performed by using the software origin.Van′t Hoff thermodynamic analysis was carried out for the intramolecular G-quadruplex oligonucleotides.Their thermal reversibility (superimposable heating and cooling profiles) allowed the calculation of the value of the equilibrium constant (K) assuming a twostate model.Application of the Van′t Hoff equation (lnK=-ΔH/RT+ΔS/R) yielded to the determination of the enthalpy (ΔH) and entropy (ΔS) of the process,as described elsewhere.Results show that the replacement of guanine bases in the middle of the three stacking quartets brings the biggest influence on the stability of the formed G-quadruplex. Data also show that potassium ions bring more stability than sodium ions to the formed G-quadruplex in most cases. It is very interesting to find that,when guanine base is replaced by cytosine or adenine at specific sites,the formed structure has comparable or even higher stability as the original sequence.
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发布时间：2021-03-19 - 摘要：Organic magnetism is a rapidly developing field that combines the skills of experimental and theoretical scientists in many areas of chemistry and physics.Compared with inorganic ferromagnet,the organic ferromagnet exhibits the characteristics of structural diversities,low density,and readily processing.In addition,layerbylayer (LBL) assembled multilayered films have received considerable interest because they allow fabrication of supramolecules with tailored architecture and properties.The design and preparation of organic soft ferromagnets by selfassembling is reported in this article.4,4′-(4,4′-Bithiazole-2,2′-diylbis(diazene-2,1-diyl))diphenol (BTDP) was first synthesized from phenol and 2,2′-diamino-4,4′-bithiazole (DABT),and the structure of BTDP was characterized by 1H-NMR.The hydroxyls of the BTDP provide anions while the poly(diallydimethylammonium chloride) (PDDA) provides cations,so the layerbylayer selfassembling of BTDP with PDDA was carried out based on the electrostatic interaction on the polyethylene (PE) surface with carboxylic acid groups (—COOH).BTDP coordinates with transition metal ions since two nitrogen atoms in the thiazole rings and metal ions can provide stable fivemember rings.Therefore,the complexes of assembled multilayer films (PE-(PDDA/BTDP-M2+)n) were also prepared via layer-by-layer assembly.The assembling process was monitored by UV-Vis spectroscopy.The linear increase of the absorbance at 413 nm with increasing the layer number indicates a process of uniform assembling.The structure of the complexes was characterized by FTIR,which suggests that the chelation has taken place demonstrated by the shift of the characteristic absorption band.In addition,the BTDP and PDDA deposition obtained by mixing their solutions could react with transition metal ions to form their metal complexes,which was also characterized by FTIR.The magnetic properties of these complexes were measured using a Physical Property Measurement System (PPMS-9),which included magnetization versus temperature,magnetization versus applied field,magnetic susceptibility versus temperature and magnetic hysteresis.The temperature is ranged from 4 to 300 K, and the intensity of magnetic field is in the range of -4×106～4×106 A/m.It was found that these complexes were organic soft magnets and had typical “S" shaped magnetic hysteresis loops.The saturation magnetization of the complex of assembled multilayer film PE-(PDDA/BTDP-Ni2+)25 is 5.30 emu/g, and the paramagnetic Curie temperature is 128 K,while the remanence magnetization and coercivity are 0.0049 emu/g and 2228.17 A/m,respectively.The results show that PE-(PDDA/BTDP-Ni2+)25is an organic soft ferromagnet at low temperatures.The magnetic properties of the multilayer film for PE-(PDDA/BTDP-Cu2+)25 is similar with those for PE-(PDDA/BTDP-Ni2+)25.The saturation magnetization of deposit complex PDDA/BTDP-Cu2+ is 2.60 emu/g, and the paramagnetic Curie temperature is -10 K,while the remanence magnetization and coercivity are 0.0035 emu/g and 2307.75A/m,respectively.The results show that PE-(PDDA/BTDP-Cu2+)25 is an organic soft antiferromagnet at low temperatures.The magnetic properties of deposition for PDDA/BTDP-Cu2+ are similar with those for PDDA/BTDP-Ni2+.In comparison,it was proved that the magnetic properties of multilayer selfassembled films were much better than those of deposited complexes.The strong ferromagnetism of the multilayered film may arise from the exchange interaction of the transition metal ions in the ligands which show a wellordered 3-D network structure.
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发布时间：2021-03-19 - 摘要：Super-hydrophobic surfaces have attracted significant attention recently,and various preparing methods have been reported,such as solgel method,plasma etching,phase separation,templatebased extrusion and so on.Besides them,the solvent evaporationphase separation was a relatively simple one,but only polymers with particular structure,such as block copolymers and polymer blends,were successfully applied by this method,Moreover,some complicate postprocedures or rigorous special environments were often essential.Herein we reported a simple way to facile a superhydrophobic surface of random copolymers just by onestep casting the polymer solution onto a solid surface.The films had many micro and nanoscale convexities and grooves with multiplex structures distributed on the surface,which appeared like a lotus leaf surface.The microscale roughness and low surface energy together endowed the films excellent superhydrophobic ability even without further modification.The water contact angle was about 155°～160°, and the sliding angle was less than 3°. The random copolymers of metharcylate (MMA) and perfluoroalkylethyl acrylate (FMA) were synthesized by microemulsion polymerization.The polymerization was carried out with sodium dodecylsulfate-C7F15COONH4-n-butanol as emulsifier,K2S2O8NaHSO3-CuSO4 redox as initiator.The emulsion was poured into excess methanol and washed by water.Then the polymer was purified several times by dissolving in acetone and precipitation by methanol.The copolymers were characterized by 1H-NMR,FTIR,GPC and fluorine element analysis.Superhydrophobic films were prepared by a onestep casting process.First,the copolymers were dissolved in F-113 to form homogeneous solutions,and then cast on 2 cm× 2 cm clean glass plates at preset temperatures in windtight environment.When the solvent was evaporated,superhydrophobic films were formed. It was found that when a good solvent of PMMA was used,such as tetrahydrofuran (THF),acetone,etc.,or the mixed solvents of THFF113,acetoneF113 etc., a smooth surface with water contact angles less than 130° was obtained.A superhydrophobic film could not gotten at these cases.It was regarded that the movement and interpretation of copolymer segments had dominative effects on the films morphology.The concentration of the polymer solution had great effect on the morphology of the films prepared.The casting solution concentration should be in an appropriate scale,the best concentration (c) was about 5×10-3 g/mL≤c≤c0,where c0 was the critical concentration of copolymer in F113.What was more,the temperature and pressure should also be proper.The possible reason of leading to the superhydrophobic properties of these films was due to the combination of micro and nanoscale binary roughness and low surface energy.The mechanism of forming these films based on the micelle aggregation model and was further discussed in this paper.These special films with both many convexities and grooves were formed because of the intrinsic properties of the random copolymer and a proper solution concentration as well as the forming conditions. In conclusion,using F113 as solvent,PFMAPFMA random copolymers can facile superhydrophobic surfaces by the solvent evaporationphase separation method.
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发布时间：2021-03-19 - 摘要：Epoxy-based photosensitive polymers with two different cinnamoyl side groups (cinnamoyl group and 4-octyloxy cinnamoyl group) were prepared by functionalization of the polymer precursor (BP-AN).Two kinds of photo-sensitive molecules including cinnamoyl groups were also prepared:hydroquinone dicinnamate obtained by reaction between hydroquinone and cinnamoyl chloride,while hydroquinone di(4-octyloxyl)cinnamate synthesized through reaction between hydroquinone and 4-octyloxy cinnamoyl chloride.All chemicals were characterized by necessary spectroscopic methods including 1H-NMR and FTIR,which indicated their accurate molecular structures had matched our target molecules.The photo-sensitive molecules were doped into corresponding photo-sensitive polymers in different proportions respectively,and photo-alignment layers were prepared based on the spin-coated films of the polymers,which were irradiated under LPUV (linearly polarized ultra violet) and then used to assemble LC cells filled with nematic liquid crystal 5CB.The photo-alignment behavior of the doped polymers was characterized by the microscopic observation and comparing the numerical value of Tmax/Tmin in sinusoid-curves of LC cells.The results showed that,below a certain doping point (about 10%),increasing the concentration of the photo-sensitive molecules would result in a better photo-alignment performance.Since the photo-dimerization reaction of cinnamoyl groups happens only when two cinnamoyl groups stand in properly spatial positions to form a tetra-atomic ring.Doped molecules greatly added up the amount of cinnamoyl pairs with adequate steric relations,thus created greater chance for cinnamoyl groups to crosslink and improved the LC-alignment performance.By doping different amount of photo-sensitive molecules we found the ideal doping point would be around 10%(np:nm).Doping content going up higher than that would lead to a worse alignment effect,with the presence of irregular patterns and luminous points under light microscope,and decreased contrast too.Luminous points were probably caused by the limited compatibility between the polymer and the doped molecules,and doped photo-sensitive molecules cumulated and became crystallized.As for irregular patterns,they are surely caused by the weak photo-alignment ability of the doped polymer.On one hand,tiny crystals would disturb the uniformity of the surface;on the other hand,it is possible that the existence of excess amount of cinnamoyl groups would both enhance photo-dimerization and photo-isomerization reactions,which are competitive reactions and lead to opposite alignment directions:photo-dimerization would align the LC molecules parallel to the polarization direction of LPUV,while photo-isomerization would align them perpendicular to the polarization direction of LPUV.At the same time,we found that LC cells doped with 4-octyloxy cinnamoyl groups showed a higher increase in photo-alignment performance,which indicated that the effect of doping varied for different systems,and this method could be rather useful for certain polymers.In a word,we’ve synthesized two novel photo-sensitive molecules and doped them into epoxy polymers to enhance the alignment ability of the material with success.In our case,the contrast could be doubled or even tripled by doping adequate amount of photo-sensitive molecules.The optimum doping amount found is around 10%,regardless of the assortments of epoxy polymers.
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发布时间：2021-03-19
Research Article
- 摘要：The bulk copolymerization of butyl acrylate (BA) and methyl methacrylate (MMA) in the presence of the RAFT agent with Z=—CH2C6H5 and 2,2′Azobis(isobutyronitrile)(AIBN) as an initiator was carried out at 60℃.The chain transfer coefficients (Ctr) at different monomer compositions were determined by the GPC peak resolution method.In the BA homopolymerization,Ctr was up to 116 while it was about 0.1 in the MMA homopolymerization.Since Ctr was too low,the homopolymerization of MMA mediated by the RAFT agent was out of control.In the copolymerization systems,Ctr showed a nonlinear decrease with the increasing of MMA compositions.When a small fraction of BA was added to an MMA polymerization system,the polymerization became well controlled with PDI around 1.2 at the end of the polymerization.The changing trend of Ctr with monomer compositions well explained the profiles of the molecular weight and its distribution against conversion with different monomer compositions.
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发布时间：2021-03-19 - 摘要：he rheological behaviors of impact polypropylene copolymer (IPC) were studied by means of dynamic rheological tests.The dynamic rheological measurements were conducted on an Advanced Rheometric Expansion System with parallel plate geometry of 25 mm diameter under air and N2,respectively.Two sorts of tests were performed under conditions as follows:(1) isothermal frequency sweeps from 100 rad#8226;s－1to 0.01 rad#8226;s－1at different temperatures from 190℃ to 230℃ in steps of 20℃;(2) isothermal time sweeps at a frequency of 0.05 rad#8226;s－1and a strain of 5% under different temperatures from 190℃ to 230℃.The development of melt structure for IPC was probed through examining the influence of temperature,atmosphere and additive antioxidant on dynamic rheological functions.Results reveal that the rheological functions vary with the increase of temperature.The second plateau appears in the logarithmic plots of the dynamic storage modulus versus frequency,lgG′-lgω,in the low ω range.Moreover,for the IPC samples exposed to N2 or blending with antioxidant,this second plateau disappears in a certain time period,being a representation of the rheological properties for homogeneous polymers.Furthermore,rheological functions in the low ω range can sensitively reflect the oxidationinduced degradation and crosslinking of IPC.
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发布时间：2021-03-19
Research Bulletin
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