最新刊期
卷 ， 期 5 ， 2008
- 摘要：The phenolic resin was synthesized by condensation of formaldehyde and phenol,with a molar ratio of 1.2,in aqueous solutions containing ammonia at 90℃ for 1.5 h under vacuum dehydration.The synthesized resin was cured at 170℃ for 3 h and then characterized by using TG under nitrogen.The cured resin was heat_treated at 300,350,400,450,500,550 and 600℃,respectively and then characterized with FTIR. In the FTIR spectra of the cured samples,the absorption bands of the methylene groups for orth-orth (o-o′),orth-para (o-p) and para-para (p-p′) substituents were at 1437～1440 cm-1，1452～1456 cm-1 and 1473～1477 cm-1 ,respectively. The variations of the individual absorbance with heat-treatment temperature were compared in terms of the relative absorbance,i.e. Ix/I1610,where I1610is the absorbance of aromatic ring backbone stretching at 1610 cm-1. The experimental results show that the thermal degradation of the phenolic resin is significantly related to the substitution position of the methylene groups.The para-substitution of methylene groups was suddenly transferred to the orth-one in some content during the condensation.Otherwise,in the cured process,para-substitution was prior formed because its activity is higher than that of the ortho-one.According to the TG and FTIR spectra,the decomposition process of methylene groups could be divided into two stages.The bond cleavages of o-o′ and p-p′ substituents occurred at 350～450℃ and 400～620℃,respectively.It means the o-o′ substituent is thermally unstable and then partially cyclized to form xanthene by intramolecular etherification.Also,the benzylic-bonded keto-intermediates could be formed through ketoenol tautomerism.The benzylic bond energy in the keto-form is at least 168 kJ/mol less than that of the original aromatic structure.Therefore,at higher temperatures,the o-o′ substituent of the methylene groups was prior decomposed. For the p-p′ substituents,the hydroxyl groups are distant form each other, and the benzylic bonded ketointermediate formation is hindered.Finally,the decomposition temperature is higher than that of the o-o′ substituents.
- 22
- |
- 15
- |
- 8
发布时间：2021-03-19 - 摘要：In order to improve the hydrophilicity of poly(lactic acid),poly(ethylene glycol)-b-poly(L-lactic acid) diblock copolymers (PELA) with different relative molecular masses and compositions were synthesized by ring-opening polymerization of L-lactide (LLA) with Sn(Oct)2 as the catalyst and methoxy poly(ethylene glycol) (mPEG) as the initiator.The structure and properties were investigated by Fourier transform infrared spectroscopy,proton nuclear magnetic resonance,contact angle measurements and differential scanning calorimetry.Results indicated that the relative molecular mass of PELA could be controlled by adjusting the feed ratio of mPEG to LLA, and the hydrophilicity of PELA increased with the increase of amount and chain length of mPEG,but the values of Tg, Tcc, Tm of PELA decreased.Ultrafine fibrous PELA membranes were prepared by traditional electrospinning from a 0.2 g/mL PELA solution in a mixture of chloroform and N,N-dimethylformamide (90∶10, V/V),and fibrous composite membranes with water-soluble poly(ethylene oxide) (PEO) as the core polymer were produced by emulsion electrospinning from a W/O emulsion solution of PEO/PELA in water/chloroform (E-PEO/PELA) and coaxial electrospinning from an aqueous PEO solution as the inner polymer solution and a PELA solution in 2,2,2-trifluoroethyl alcohol as the outer polymer solution (C-PEO/PELA),respectively.Characterization by scanning electron microscope and transmission electron microscope verified the fine fiber morphology of the above three kinds of the obtained electrospun fibers.The hydrophilicity of the electrospun PELA membranes increased with their content of mPEG.Core/shell E-PEO/PELA and C-PEO/PELA fiber structures were obtained by both emulsion electrospinning and coaxial electrospinning,meanwhile their hydrophilicity was better than that of the electrospun PELA membrane because of the special core/shell fiber structure and PEO in the core.
- 24
- |
- 17
- |
- 6
发布时间：2021-03-19 - 摘要：The preparation of core-shell fibers was of particular interest for those core materials that would not form fibers via electrospinning by themselves,and co-electrospinning could also facilitate manufacturing of polymer nanotubes.Furtheremore,coaxial electrospinning would provide an alternative and simple means to encapsulate drugs to deliver a biomolecular drug in a sustained fashion.In this study,core-shell structured chitosan (CS)/poly(vinyl alcohol)(PVA)-poly(propylene carbonate) (PPC) fibers were prepared by coaxial electrospinning.The coaxial electrospinning setup in this study was a compound spinneret,consisting of two concentrically arranged capillaries that were flatted stainless steel needles.A certain amount of the two polymer solutions were contained separately in two plastic syringes connected to the coaxial spinneret,and the flow rate in each capillary was adjusted in a double-way medical syringe pump.The liquid flowing on the outside was PPC solution,and the inner liquid was CS/PVA solution.First,the effects of mixed solvents on electro-spinnability of PPC solutions were investigated to choose an appropriate solution system using a conventional electrospinning setup.The properties of PPC solutions in chloroform/dimethylformamide (DMF) mixed solvents with different volume ratios were tested,and the solution conductivity had a tendency to increase ranged from 0.02 to 13.43 μs·cm-1 when DMF proportion had increased.The morphology and diameter of fibers were determined with scanning electron microscopy (SEM).The results indicated that the use of chloroform/DMF (1/1) mixed solvents could avoid agglomeration of polymer at the capillary tip during coaxial electrospinning process,and contributed to good morphology and most narrow fiber distribution of the fibers (300～600 nm). Secondly,the morphology and structure of the core-shell fibers were characterized by SEM and transmission electron microscopy (TEM).In addition,hydroxyapatite (HAp) was successfully encapsulated into the core of composite fibers,which was characterized by fourier transform infrared spectroscopy (FTIR).The SEM and TEM observation indicated that the total diameter of the CS/PVA(core)-PPC(shell) fibers amounted to about 300 nm,whereas the diameter of the core region was about 60 nm.The core-shell structure could clearly been seen with a sharp interface between the core and shell fiber.In some cases,however,the interface was perturbed,due to an onset of instability.The diameter range of core-shell structured fibers was broader than general single-fluid electrospun fibers,which attributed to the flow instability of the inner dope and the bending instability during the electrospinning process.FTIR results showed the appearance of a peak at 1038 cm-1 due to the PO3-4 wagging,which confirmed the presence of HAp in the final fibers.The present study would provide a basis for further design and optimization of processing conditions to control the structure of core-shell composite fibers,and ultimately obtain novel functional biomimetic fibers applied in drug release and tissue engineering.
- 24
- |
- 13
- |
- 5
发布时间：2021-03-19 - 摘要：The micellar solutions of sodium dodecylsulfate (SDS) and sodium 2-acrylamidododecane sulfonate (NaAMC12S),which is a surface-active monomer,were prepared,and the solubilization properties of N-dodecylacrylamide (C12AM),which is a strong hydrophobic monomer,in the two micellar solutions were determined.Based on this determination,the micellar copolymerization of acrylamide (AM) and C12AM was performed in the two micellar solutions,and bipolymer C12AM/AM and terpolymer C12AM/NaAMC12S/AM were obtained,respectively.Their infrared spectra were measured,and the structures were characterized.Their hydrophobic association properties and rheological behavior were mainly studied by using fluorescence probe technique and viscosimetry.The experimental results show that in the micellar solution of surface-active monomer NaAMC12S,the copolymerization of AM and hydrophobic monomer can be realized favorably.Because the surfaceactive monomer also participates in the copolymerization,the product is a terpolymer,C12AM/NaAMC12S/AM.As compared with the biopolymer C12AM/AM,the terpolymer has stronger hydrophobic association properties owing to the incorporation of the surfaceactive monomer NaAMC12S.But then the contribution of the strong hydrophobic monomer,C12AM,to the hydrophobic association of the terpolymer is the main one,whereas the surface-active monomer,NaAMC12S,only plays an assistant role.To prepare hydrophobically association polyacrylamide (HAPAM) in the micellar solution of surface-active monomer not only simplifies the process of micellar copolymerization owing to avoid the procedure of removing surfactants,but also enhances the hydrophobic association properties of HAPAM.Therefore,the method put forward in this work is a significant improvement for the conventional micellar copolymerization.
- 16
- |
- 11
- |
- 3
发布时间：2021-03-19 - 摘要：The synthesis of poly(2-hydroxylthyl methacrylate) grafted soy protein isolates (SPI-g-PHEMA) using atom transfer radical polymerization (ATRP) was described.Poly(2-hydroxyethyl methacrylate) (PHEMA) is one of most extensively studied biocompatible polymer,which has been used for applications such as contact lenses.The scheme of the work was that the soy protein isolate macroinitiator (SPI-Br) was synthesized first by condensation reaction of the active amino groups and 2-bromoisobutyryl bromide,and the resulting secondary bromide could be used as initiator for HEMA monomer in atom transfer radical polymerization to propare SPI-g-PHEMA.FTIR and 13C-NMR spectra confirmed the conversion from SPI sequence to SPI-Br.Atom transfer radical polymerization of 2-hydroxyethyl methacrylate (HEMA) on SPI was carried out in aqueous solutions using SPI-Br as initiator,copper chloride/bipyridine (CuCl/bpy) as catalyst.FTIR spectrum was used to characterize the successful polymerization of HEMA onto SPI globulin.The graft chain was cleaved from SPI-g-PHEMA by degradation of hydrochloric acid for purpose of the measurement of molecular weight of graft chain by GPC.The changes in the spectra of SPI,SPI-Br,SPI-g-PHEMA and grafted chain confirmed successive steps in the synthesis of SPI-g-PHEMA hybrids.A series of comparative experiments were taken with different reaction mediums（H2O,H2O/n propanol, n-propanol）,and higher molecular weight result was gained in aqueous solutions by ATRP.The number average molecular weight was about 1.16×104,and a polydispersity was about 1.12,so the water medium system was chosen for further study.The molecule weight and the polydispersity of graft chain cleaved from SPI-g-PHEMA prepared via ATRP initiated by soy protein isolate macroinitiator were similar to those of PHEMA prepared by normal ATRP using 2-bromoisobutyryl bromide without SPI in solution under similar reaction conditions.The solution properties of SPI-g-PHEMA were characterized by UV and fluorescent spectrophotometer.The results indicated that with increasing of pH value,the solubility of SPI and SPI-g-PHEMA increased,and the hydrophobicity decreased.The zeta-potential of SPI and SPI-g-PHEMA solutions were also studied by zeta-potentiometer.The static charges on the surface of SPI molecules increased clearly after graft modification,and the values of the zeta potential of SPI and SPI-g-PHEMA solutions decreased with the increase of pH values.The TEM images showed that the diameter of SPI-g-PHEMA was beyond that of SPI,and the morphologies of SPI and SPI-g-PHEMA were different.
- 23
- |
- 12
- |
- 3
发布时间：2021-03-19 - 摘要：By the synthetic method of chemical oxidative polymerization,conducting polyaniline (PANI) doped with vanadium-containing molybdicacid (HPA) had been prepared by template synthesis within porous anodic aluminum oxide (AAO).The porous anodic aluminum oxide membranes were immersed in the aniline monomer solution,and a vacuum was kept until no air bubble gave off in the AAO templates;in this case,the template channels were full of the aniline monomer,the HPA solution was dropped into aniline solution,and reaction was initiated inside the channels to form one-dimensional nanostructures PANI.The nanowires of the PANI were characterized by Fourier transform infrared spectroscopy (FT-IR),the X-ray diffraction (XRD),the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM).The XRD and FT-IR spectra analysis provides evidence for the HPA/PANI that the PANI could be effectively doped by the HPA,and the HPA existed with molecular state in the materials,and the materials are of non-crystalline structure.The surface morphology of the HPA/PANI nanowire arrays was observed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The SEM and TEM information show that the PANI nanowires are about 80 nm in diameter.Furthermore,the thermal stability and the conductivity of doped PANI were also determined.The materials have three steps in the thermal analysis,losing adsorbed water process,losing crystalline water of the HPA structure and continous decomposition process of the PANI structure and HPA structure decomposition process.The conductivity of the HPA/PANI was determined to be 16.2 S·cm-1.In the polymerization process,the HPA not only acts as protonic acid,but also oxidant and dopant.The polymerization follows a radical mechanism:In the first the aniline is protonated by HPA,and then HPA further oxidates aniline cationic radicals.The aniline is induced to generate the quinoid dimine cationic radicals and bensoid cationic radicals,the formation of the PANI long chain results from coupling of two cationic radicals.The electron transfers from benzenoid ring segments to quinoid ring segments and further fabricates the model structure of tetracyclic anamorphosis of the benzenoid-type and quinoid-type in the chain structure of the PANI.The doping reaction undergoes in two steps,formation of the quinoid dimine cationic and their coupling with bensoid cationic radicals.
- 20
- |
- 13
- |
- 5
发布时间：2021-03-19 - 摘要：Hyperbranched polyethylene (HBPE) is a new type of polyethylene materials in addition to low-density polyethylene (LDPE),high-density polyethylene (HDPE),and linear low-density polyethylene (LLDPE).It has dendrimer-like compact globular structures.Due to lack of chain entanglements,it exhibits better solubility and lower viscosity than the other types of polyethylene.HBPE has attracted great attention in the recent years in both academic and industrial researches.However,as polyolefin materials,HBPE suffers from such shortcomings as nonpolar nature and thus lack of functionalities.These shortcomings limit its applications.Grafting of polar molecules such as maleic anhydride (MAH) has been widely adopted in the modification of polyolefins. In this work,HBPE samples having high molecular weight (Mw=8×10.6 g/mol) and high branching density (the number of branches per 1000C=108) were synthesized by solution polymerization of ethylene with a late transition metal catalyst,namely bi(2,6-diispropylphenyl) butane diimine nickel dibromide (IBNB) at 45℃ and 0.5 MPa. The Ni catalyst is well-known to experience a chain walking mechanism that is responsible for the hyperbranched chain topology. 1H-NMR and 13C-NMR were used to examine the branching density and the type of branches,respectively.It was discovered that the types of branches were mainly methyl (50.54%) and butyl (20.30%). MAH was grafted onto HBPE through a free radical mechanism.Di-tert amyl peroxide (DTAP) was used as the free radical initiator.However,it was found that the HBPE/MAH/DTAP grafting system experienced severe chain degradation and crosslinking side reactions during the grafting process. N,N-diethyl cinnamamide (DECA) was thus synthesized by the use of cinnamoyl chloride,diethylamine,and triethylamine which was used as an acid-binding reagent.DECA was then used as an inhibitor to suppress the side reactions.The approach was successful and efficient.The gel content in the grafting products was remarkably reduced from 55.38% to 5.15%.The Mw was almost doubled in reference to the use of MAH and peroxide DTAP only.The observation suggests that the chain degradation and crosslinking side reactions were dramatically suppressed with the addition of DECA. Compared to the other investigated inhibitors such as styrene (St), N,N-dimethylacetamide (DMAC),3-(2-furyl)acrylic acid (FAA) and ethyl cinnamate (ECA),DECA was found to be the most effective in suppressing both chain degradation and crosslinking side reactions.We also found that FAA and ECA could effectively suppress the chain degradation in the grafting system,but the grafting system had high gel contents and experienced severe crosslinking.St and DMAC had some effects on inhibiting crosslinking,but there was still small amount of crosslinking.The proposed mechanism is that DECA reacts first with HBPE macroradicals to form stable macroradicals when DECA is added to the grafting system.The latter then reacts (or copolymerizes) with MAH to form MAH-grafted HBPE.Because the formed stable macromolecules contain amide group,both the chain degradation and crosslinking side reactions are effectively suppressed.In general,in the presence of radical initiator,HDPE mainly experiences crosslinking,while polypropylene undergoes chain scission.LDPE and LLDPE have both reactions simultaneously occurring.HBPE is more or less similar to the low-density materials having simultaneous crosslinking and degradation.In the grafting studies,these side reactions need to be controlled.The current work elucidates the grafting mechanisms and provides practical guidance in this regard.
- 33
- |
- 16
- |
- 2
发布时间：2021-03-19 - 摘要：Poly(methyl methacrylate) (PMMA) is one of the matrix polymers commonly used in gel polymer electrolytes,and has been proposed for lithium battery applications.PMMA-based gel polymer electrolytes (GPE) show high ionic conductivity at ambient temperatures.However,low thermal stability and mechanical properties with hard forming freestanding film in gel systems at high organic solvents will limit its application.In order to overcome these problems, methyl methacrylate (MMA)-maleic anhydride (MAh) (P(MMA-co-MAh) ) copolymer was prepared,in the copolymer the ring structure of MAh units can improve the thermal stability and mechanical properties,consequently,improving the thermal stability of P(MMA-co-MAh)-based gel polymer electrolytes.The copolymer of P(MMA-co-MAh) was synthesized through solution copolymerization with toluene as solvent,2,2′-azobisiobutyronitrile (AIBN) as the initiator, MMA and MAh as the monomers with the molar ratios of MMA∶MAh monomer is 1∶1 The reaction was carried out at 80℃ under nitrogen atmosphere for 8 h. The structure and properties of the copolymer were characterized by Fourier transform infrared spectroscopy (FTIR), 1H-nuclear magnetic resonance (1H-NMR),X-ray diffraction (XRD),gel permeation chromatography (GPC),thermogravimetric analysis (TGA),differential scanning calorimetry (DSC).It was found that the unsaturated bonds existed in both of MMA and MAh (1637 cm-1) disappeared in the copolymer,whereas a strong absorption peak at 950 cm-1 for O=C-O-C=O ring stretching vibration of a saturated cyclic five-membered anhydride and a peak at 1445 cm-1 for —CO—O—CH3 stretching vibration of MMA were observed in the FTIR spectrum,respectively.The 1H-NMR spectrum of P(MMA-co-MAh) copolymer showed four peaks,and the peaks at δ=2.65～3.20 and 3.5～3.8 represent the chemical shift of H for MAh groups and —COOCH3 groups,respectively,indicating the molecular structure of copolymer P(MMA-co-MAh).The molar ratios of MMA and MAh in the P(MMA-co-MAh) copolymer is 8∶1. XRD showed that the P(MMA-co-MAh) was a typical amorphous polymer,which is beneficial in improvement of ionic conductivity of its GPE.GPC resalts show that the number average molecular weight (Mn) of the copolymer is 6.40×104 and the mass average molecular weight (Mw) is 6.68×104; the molecular weight distribution (Mw/Mn) is 1.04 The TGA curves show that the thermal degradation temperature of P(MMA-co-MAh) is 300℃,which is higher than that of the pure PMMA polymer.The DSC results of the P(MMA-co-MAh) copolymer reveal that the glass transition temperature (Tg) is 121.3℃,which is higher than that of the pure PMMA.The gel polymer electrolyte was prepared from the P(MMA-co-MAh) copolymer,propylene carbonate (PC) and lithium perchlorate.It is found that the GPE can form free-standing films.The ionic conductivity is 3.0×10-5 S/cm at room temperature for 45 wt% P(MMA-co-MAh) gel copolymer enlectrolyte with 55 wt% 1 mol/L LiClO4-PC solution.The ionc conductivity for GPE of P(MMA-co-MAh) copolymer is lower than that of the gel polymer electrolytes of pure PMMA containing 50 wt% PMMA with 50 wt% 1 mol/L LiClO4-PC solution.
- 28
- |
- 11
- |
- 4
发布时间：2021-03-19 - 摘要：This study presents the elasticity of single polyethylene (PE) chains with one end fixed based on the steered molecular dynamics (SMD) method.During the tensile process,we find that the average pulling force 〈f〉 displays a dependence of pulling velocity v When the pulling velocity v 0.05 nm/ps,the average pulling force 〈f〉 increases first and then keeps a plateau of a constant force around 250 pN.The shape factors of the polyethylene (PE) chain are investigated during the pulling process.Here,〈δh〉、〈δm〉 and 〈δt〉 are the shape factors of the head segment,middle segment and the tail segment of the single polyethylene (PE) chain.We find that 〈δh〉 and 〈δt〉 increase obviously in the low extension area,but〈δm〉 keeps unchanged.However,〈δm〉 increases rapidly in the high extension area.We conclude that the shape of the head segment and tail segment of the polyethylene (PE) chain change first,and then the shapes of the middle segment changes during the pulling process.If we sequentially release the stretching chain,the polyethylene (PE) chain exhibits force hysteresis.This means that the stretching and releasing follow different paths.The results agree well with the experimental results of the force hysteresis by Kellermayer et al.The force extension curves display hysteresis because the pulling velocity at which the single polyethylene (PE) chain is stretching and the release exceedal the velocity of molecular thermal fluctuation.The area enclosed by the force hysteresis represents the dissipated energy〈Ed〉,which has a relationship with pulling velocity v.Behavior of 〈Ed〉v can be fitted with a curvilinear equation of〈Ed〉=a+b×e-cv,and shows two distinct cases:a weak dependence as v0005nm/ps,〈Ed〉 almost keeps unchanged with the increase of the pulling velocity v, and a strong dependence as v0.005 nm/ps,〈Ed〉 increases obviously with the pulling velocity v. Furthermore,at different thermodynamics temperature areas of single polyethylene (PE) chain,〈Ed〉 shows different behaviors.At high temperature areas T220 K,〈Ed〉 decreases with the increase of the temperature,which agrees well with the experimental results of energy dissipated in a loading-unloading cycle of poly(butylene terephthalate) by Pegoretti et al. However,the experiment can’t be realized at low temperature.Our computer simulations can overcome the unaccessible condition in real experiments.We find that 〈Ed〉 decreases with the decrease of the temperature at low temperature area T220 K.All these investigations may provide some insights into the elastic behavior of polymer chains.
- 17
- |
- 13
- |
- 3
发布时间：2021-03-19 - 摘要：SalenAl(OiPr) complex,prepared by reaction of SalenH2（N,N′-bis(salicylidene)-1,2－phenylenediamine） and isopropoxide aluminum,has been shown to be an effective catalyst for the coupling of carbon dioxide and cyclohexene oxide to afford poly(cyclohexenylene carbonate) (PCHC) with small quantities of byproduct. The addition of various cocatalysts,including 4-dimethyl(amino) pyridine (DMAP),N-methyl imidazole (N-MeIm),1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and tetra-n-butylammonium chloride (Bu4NCl) can greatly enhance the catalytic efficiency,and more donating DMAP can offer the best copolymerization result.The relative DMAP loading also plays an important role in polymer formation.Experiments indicated that 1 equiv of DMAP was the optimum cocatalyst loading.At higher cocatalyst loading,there is a little increase in polyether linkages as well as a dramatic decrease in the molecular weight of the coplymer. Effects of reaction condition such as catalyst concentration,reaction time,temperature,CO2 pressure on copoymerization were probed in detail.Through varying catalyst concentration,it was found that both lower and higher catalyst concentration led to lower catalytic efficiency and lower Mw,and maximum catalytic efficiency was observed in the presence of catalyst concentration around 2 g/L.The catalyst concentration seemed not to influence the carbonate content in the copolymer significantly.Almost in all cases highly alternative copolymers were obtained.As far as reaction time is concerned,the catalytic efficiency and molecular weight are enhanced with increasing time at the beginning,it reaches a maximum around 32 h,and then drops slowly.Carbonate content as low as 96.5% was observed at the very beginning,afterward the copolymerization quickly tended to proceed alternatively.Both the catalytic efficiency in copolymerization and molecular weight of PCHC raised with increasing reaction temperature from 40℃ to 80°C.At temperatures above 80℃,the polymer yield and molecular weight went down with further increasing temperature due to serious degradation of the obtained polymer.Increasing CO2 pressure,while was less than 4 MPa,enhanced the catalytic efficiency.Higher pressure favored the formation of alternative copolymer as expected,but rather high CO2 pressure was harmful to copolymerization. In conclusion,the best results were obtained from the reaction at 80℃ for 32 h,with 2.0 g/L SalenAl(OiPr) and CO2 pressure of 4 MPa using 1.0 equiv of 4-dimethylaminopyridine (DMAP) as cocatalysts.The highest turnover number (TON) is 495 g of polymer/g of catalyst.The produced copolymer is completely alternated polymer (percent of carbonate 99%),and had a Mn value of 55900 with a polydispersity index of 1.32 as determined by gel permeation chromatography.On 13C-NMR spectroscopy,chemical shifts observerd at 153.7,153.2,and 153.0 indicate the production of largely atactic polymer.The thermal properties of the copolymer were obtained by means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in N2 and at a heating rate of 10 K/min.DSC showed that the high alternating PCHC copolymer exhibited higher glass transition temperature (136℃) than their corresponding values reported in the literature,and TGA results indicated that the high alternating PCHC copolymer began its decomposition at 280℃ and then decomposed completely upon 350℃.The high alternating PCHC has excellent thermal decompose properties,and can be applied as MEMS sacrificial material.
- 25
- |
- 18
- |
- 2
发布时间：2021-03-19 - 摘要：High refractive index polyimides (PIs) have been widely utilized for the fabrication of microlens for CMOS image sensors (CIS).In the present work,a series of semi alicyclic Pis were developed from an alicyclic dianhydride,2,3,5-tricarboxycyclopentylacetic acid dianhydride (TCAAH) and two sulfur-containing aromatic diamines,4,4′-thiobis［(p-phenylenesulfanyl) aniline］ (3SDA) and 2,7-bis(4-aminophenylenesulfanyl) thianthrene (APTT). As a typical example,PI-1 was prepared according to the procedure described below.3SDA (8.6524 g,20 mmol) and freshly-distilled NMP (30.0 g) were added to a 100 mL three-necked round-bottom flask equipped with a high-power electromagnetic stirrer,nitrogen inlet and cold-water bath.A clear diamine solution formed after stirring for 30 min under a nitrogen flow. Then,TCAAH (4.4834 g,20 mmol) was added immediately,followed by additional NMP (22.5 g) to adjust the solid content of the mixture to be 20 wt%.The mixture was stirred at room temperature for 24 h to afford an almost colorless,highly-viscous solution,which was diluted to 15 wt% by adding additional NMP.The mixture was purified by filtration through a 0.45 μm teflon syringe filter to obtain the poly(amic acid) (PAA) solution (PAA-1).The PAA-1 solution was spin-coated on a silicon wafer or quartz substrate.The thickness was controlled by adjusting the spinning rate.PI-1 film was obtained by thermally curing the PAA solution under nitrogen in an oven at 80℃ for 3 h ,120℃ for 1 h,180℃ for 1 h,250℃ for 1 h,and 300℃ for 0.5 h,then,the film was obtained by immersing the substrate in warm water.PI-2 film (TCAAH-APTT) was synthesized with a similar route. The structure of the PI films was confirmed by FT-IR measurements,in which the characteristic absorptions of imide moiety were clearly observed.The thermal properties of the PI films were evaluated by TGA,DSC,and DMA measurements.The results indicated that the PI films exhibited good thermal stability up to 480℃ and glass transition temperatures higher than 250℃. The PI films showed good optical transparency in the visible light region (400～700 nm) with the transmittance higher than 85% at 400 nm.The refractive indices of the PI films were higher than 1.68 at 632.8 nm， and the birefringence values were lower than 0.006.The refractive index of the PI could further be increased by mixing with silica-modified titanium dioxide (TiO2) nanoparticles. For example,PI-I/TiO2 nanocomposite film was successfully prepared by the mixing of PAA-1 and TiO2 with the ratio of PAA-1∶TiO2=55∶45 (wt%).The nanocomposite film showed transmittance of 88% at 400 nm,slightly lower than that of PI-I (96%).The film had refractive index of 1.76 at 632.8 nm.The preliminary results indicated that the refractive indiex of the nanocomposite film increased with increasing the TiO2 content.However,how to maintain the high optical transparency of the films is a challenging topic.
- 37
- |
- 16
- |
- 7
发布时间：2021-03-19 - 摘要：A series of poly(n-alkyl-acrylate)s (PAAn) and poly(octadecyl acrylate-co-n-alkyl acrylate)s (P(AA18-co-AAn)) (n,the side chain carbon number) were synthesized with AIBN as initiator at 60℃ for 24 h in nitrogen atmosphere.The molecular weight of the polymers and the polymer dispersity index were measured with gel permeation chromatography (GPC).The thermal behaviors of PAAn and P(AA18-co-AAn) were studied by differential scanning calorimetry (DSC).The results manifest that，for homopolymers,there is a gradual increase of fusion heats and melting points with the side-chain carbon number ranging from 10 to 20,because more units of methylene enter into the crystal lattice for PAAn with longer side chains length.At the same time,the melting endothermal peak of PAAn was not detected in DSC running as the n was less than 10,which meant that 10 was the critical side chain carbon number for the discrimination of crystallizable and non-crystallizable PAAn.For copolymers of AA18 with crystalline homologous AAn (n=10,12,14,16) series,the crystallinity (Xc) of copolymers was between the values of the corresponding homopolymers,and it increased with increasing the content of AA18,and the corresponding melting ranges had a maximum value at certain AA18 content.The value of extent of equilibrium crystallinity (Xc/Xcmax) of P(AA18-co-AA14) and P(AA18-co-AA16) changes little with increasing content of AA18,because the side chain carbon number of monomers has little difference and the affection of the other side chain is small.While the Xc/Xcmax of P(AA18-co-AA10) and P(AA18-co-AA12) increases at first and then decreases.The more difference of side chain carbon numbers (18/12,18/10) led to the interactional disturbing effect,and many defects would occur during crystallization.At the same time,the shorter side chain length of AA10 and AA12 decreased the crystallizing ability obviously resulting in much less Xc.For the copolymers of AA18 with non-crystalline homologous AAn (n=4,6,8) series,both Xc and Xcmax increased with increasing content of AA18,since AA18 was the only crystallizable component.With increasing the side chain carbon number of non-crystalline homologous AAn series (n=4,6,8) of the same AA18 mole fraction,the values of Xc/Xcmax decreased,while the maximum values of melting range almost kept constant.
- 22
- |
- 12
- |
- 1
发布时间：2021-03-19 - 摘要：Microcracks are easily generated inside polymers and polymer composites during their service in structural applications.Development and coalescence of microcracks would bring about catastrophic failure of the materials and then reduce their lifetimes.Therefore,early sensing,diagnosis and repair of microcracks become necessary for removing the latent perils.In this context,the materials possessing self-healing function are ideal for longterm operation.Attempts have been made to develop solutions in this filed,among which the route based on microcapsulation seems to be promising.Self-repairing polymer composites containing microencapsulated healing agent have attracted more and more research interests.The present article analyzed the existing problems and proposed the criteria for manufacturing qualified microencapsulated healing agent.Accordingly,microcapsules containing epoxy resin were successfully fabricated by in situ polymerization in an oil-in-water emulsion with poly(melamine-formaldehyde) (PMF) as the shell material and high-activity lowviscosity diglycidyl tetrahydro-o-phthalate (DTP) as the core substance.The typical synthesis procedures are described below.About 50 g DTP was added into 250 mL aqueous solution of 2% styrene-maleic sodium (SMS).The mixture was vigorously agitated by a homogenizer for 10 min at a selected rate and then two drops of 1-octanol were added to eliminate surface bubbles of the emulsion.The pre-condensate of 12.5 g melamine and 27.1 g formaldehyde was prepared at 70～75℃ for 30 min, and the pH value of the solution was kept at about 9～10 by adding triethanolamine.Subsequently,the pre-condensate solution was added to the above emulsion with 450 r/min continuous mechanical stirring by a two-bladed stirring paddle while the pH value of the solution was adjusted by adding citric acid.Eventually,the reaction mixture was cooled down to room temperature.The resultant slurry was neutralized by 2% sodium carbonate solution,and then diluted with deionized water.The deposit of microcapsules was separated through a Buchner funnel and rinsed with deionized water and then vacuum dried.The synthesis method was improved by optimizing the processing parameters.The appropriate reaction time was about 30～60 min.Further extension of time had little influence on the products.The reaction temperature should be set at about 50～70℃.The pH value of about 3.2 was appropriate and had complex effect on the properties of the products.The appropriate core/shell mass ratio was about 2∶1～3∶1.The size and size distribution of microcapsules were mainly determined by the dispersion rate and the emulsifier content.Having been encapsulated,the core material DTP kept the same activity as its raw version.The microcapsules’ shell wall was relatively thin (ca. 0.2 μm),which assured sufficient core content (83.2 wt%) even if the microcapsules were very small (ca. 6.7 μm).Moreover,the microcapsules were proved to be strong enough to survive handling during manufacturing self-healing composites.Having been preembedded in cured epoxy,the microcapsules had satisfied affinity to the matrix.They can be readily ruptured releasing DTP fluid as expected upon damaging of the composite,and activity of the released core material was the same as the raw material.Besides,the microcapsules had good sealing ability and high stability.They can be stored at room temperature for long time and could bear moderate or high temperatures applied for curing composites.The present work provided a new simple approach for mass-production of epoxy loaded microcapsules,which can be used to manufacture self healing composites or other self-curing stuffs like single constituent epoxy adhesive and self-locking threaded fasteners.
- 39
- |
- 20
- |
- 24
发布时间：2021-03-19 - 摘要：A partially miscible polymer blend can be homogeneous or heterogeneous depending on its composition and temperature.The phaseseparated blend and its homogeneous counterpart have different internal structures and thus show different viscoelastic properties,which have received considerable attention in the past few decades.It has been found that the homogeneous blends,as their constituents,typically exhibit simple thermorheological behavior,and their rheological functions at different temperatures can fall on the same curve using time-temperature superposition (tTS); on the other hand,the phase-separated blends display pronounced elasticity in the terminal region,which makes the tTS principle invalid for them,and show thermorheological complexity.Such enhanced elasticity causes a discontinuity in the temperature dependence of the storage modulus at low frequencies.These characteristic fingerprints,in turn,have been used not only for characterizing the miscibility of partially miscible polymer blends but also even for quantitatively estimating the phase boundary.The phase separation (binodal) temperatures were marked by a change in the slope of the curve of the dynamic storage modulus versus temperature.However,the apparent phase separation temperatures obtained by rheological tests are frequency dependent,and lower or higher than the binodal temperatures detected by other methods such as turbidity method when lower and higher frequency is applied,respectively.There is still no general knowledge on what causes these divergences.In addition,it is unknown that what size of domains the rheological method can resolve up to now.Experiments and discussion in this paper tries to overcome these problems.The phase separation temperatures of partially miscible poly(styrene-co-maleic anhydride)/poly(methyl methacrylate) blends have been determined using small amplitude oscillatory shear (SAOS) test by dynamic frequency sweep mode and using small angle light scattering (SALS) method.It has been found that,as reported in the literatures,the phase separation temperatures obtained by rheological methods are frequency dependent and lower or higher than those obtained by SALS measurements when a frequency of 0.1 or 0.4 rad/s is applied.The relative increases of the storage moduli of the phaseseparated blends at different frequencies are compared at the same temperature,where the dynamic moduli of the phase-separated blends were obtained by rheological measurements,and those of their homogeneous counterparts were evaluated by the double reptation model.The results indicate the enhanced storage modulus caused by the phase separation at lower frequency is more sensitive than that at higher frequency.In order to probe resolution scale of rheological method for determining phase separation temperature,the Parlierne model was applied to evaluate the size of droplets.The results indicate that,in the present case,rheological measurements at 0.1 rad/s and 0.4 rad/s frequencies can resolve the size of domains over a 100 nm and 700 nm scales,respectively.According to these results,we argue that the divergence between the rheological binodal curves at different frequencies is attributed to the different sensitivity of rheological measurements at different frequencies,and compared with the size of domains over a 500 nm scale resolved by small angle light scattering,the rheological method can be more sensitive when the lower frequency is applied.
- 26
- |
- 11
- |
- 6
发布时间：2021-03-19
Research Article
- 摘要：Three cross-linking polystyrene resins functionalized with formylgroups, p-formylphenoxymethyl, p-formyl-2-methoxyphenoxymethyl and p-formyl-3-methoxyphenoxymethyl were reduced by NaBH4 under phase transfer catalytic conditions coupling with microwave irradiation (MI-PTC),and three benzylhydroxyl resins,the Wang resin,Sasrin resin and a novel p-benzylhydroxyl-3-methoxyphenoxymethyl resin were correspondingly obtained.The preparations of these resins were carried out under heating in water batch and microwave irradiation.The reaction monitoring was performed by FTIR,and the contents of hydroxyl groups of target resins were determined by nitrogen element analysis involving derivative reaction of 3,5-dinitrobenzoyl chloride.The influence factors such as solvent and phase-transfer catalyst were experimentally investigated.The optimized solvent was THF/H2O among DMF,ethanol,THF,and THF/H2O,and the optimized phase-transfer catalyst was benzyltrihydroxylethyl ammonium chloride (BTHAC) among BTHAC,PEG-400,cetyl trimethyl ammonium chloride (CTMAC),tetrabutylammonium chloride (TBAC).However,the mixture ratio of the optimized solvent was different for reations with traditional heating and microwave irradiation.Under heating in water batch,the optimized solvent was 12 mL THF+3 mL H2O,while that was 3 mL THF + 12 mL H2O under microwave heating.The polymer-supported formyl groups were almost quantificationally converted into hydroxyl groups in 30 minutes under the optimized conditions and 60 W power microwave input,while under the traditional heating the reaction time exceeded 24 h and the conversion extent of formyl groups was somewhat less.Compared with that of conventional heating,the reduction of formyl supported by cross linking polystyrene under MI-PTC by NaBH4 was a good method with short reaction time and improved conversion.
- 14
- |
- 11
- |
- 0
发布时间：2021-03-19 - 摘要：Ring-opening metathesis polymerization (ROMP) is a widespread tool to synthesize well-defined and highly functionalized polymers.Recently,the ROMP of 5-substituted cyclooctene with the pendant of imidazolium salt catalyzed by Grubbs second generation catalyst ［RuCl2(PCy3)(SIMes)(CHPh)］ in CH2Cl2 and ionic liquid was reported.The polymerization,which was carried out in CH2Cl2,afforded much higher number average molecular weights (Mn) and a much broader molecular weight distribution (PDI) than those expected for a living polymerization.These results imply that,with functionalized cyclooctene monomer propagation is significantly faster than initiation resulting in a poor initiation efficiency.Additionally,the broadening PDI of polymers may be due to its propensity to perform intramolecular backbiting reactions.This is a general phenomenon in ROMP initiated with ［RuCl2(PCy3)(SIMes)(CHPh)］ in conventional organic solvents.However,the polymerization,which was carried out in ionic liquid,afforded improved control over the molecular weight and polydispersity of the resultant product (PDI1.4).This polymerization showed many of the characteristics of a living system which prompted us to look more closely at the kinetics of this particular system.The first investigation for kinetics of the initiation and propagation of ring-opening metathesis polymerization of 3-methyl-1-［(5-cyclooctenyl)oxycarbonylmethylene］-imidazol-1-ium tetrafluoroborate catalyzed by ［RuCl2(PCy3)(SIMes)(CHPh)］ in ionic liquid and CDCl3 was carried out by 1H-NMR spectroscopy measurement.The decrease in the monomer concentration over time was tracked by the monitoring of the decrease in the resonance of the alkenes protons on the cyclooctenes ring which appeared atδ=5.5～5.7 relative to an internal standard of CDCl3.These proton signals shifted upfield to approximately δ=5.38～5.39 as the undertaking of reaction,this indicated that the polymerization had occurred,and the monomer had turned to be polymer.The polymerization performances were much different in CDCl3 and ionic liquid. 1H-NMR studies have revealed that the initiating carbene,which shows a signal for the alkylidine proton at δ=19.2 in CDCl3,is converted into the propagating carbine with a remarkable peak change from broad to sharp over time.The multiplicity and broadening of the resonances are consistent with a multiplicity of overlapping environments associated with irregular living chain terminal.The polymerization was also monitored by 1H-NMR in ionic liquid,within the limits of NMR sensitivity,signals attributed to the propagating carbine (δ=19.2) maintained a relatively same intensity throughout the polymerization which meant a constant concentration for the living propagating chain.The plot of ln［M］0/［M］ versus reaction time was found to be linear in ionic liquid,and the results demonstrated the absence of chain termination on the timescale of the polymerization and showed the polymerization was conducted with living characteristics.The reaction kinetic equation for the polymerization process in ionic liquid was also determined.The exact nature of the propagating species in ROMP is unknown,but we assume that the living characterization is ascribed to the relatively slow propagation of monomer because of the interaction between the charge of monomer and medium of ionic liquid.
- 19
- |
- 14
- |
- 1
发布时间：2021-03-19 - 摘要：Micropatterned thin films have received increased interest in the past few years for use in chemistry and life sciences.Although they can be prepared either by conventional lithography1 or by soft lithography,but most of the methods require expensive and delicate equipment which limits their applications in some areas to a certain degree.A variety of polymers have been reported to be able to form ordered microporous films by water-assisted fabrication.But most of these polymers,include linear homopolymers,rod-coil or coil-coil block copolymers,star-like homopolymers or copolymers, et al. were synthesized under special design.Therefore,it is still desirable to develop simple techniques to prepare micropatterned polymer films.Chinese lacquer is a natural polymeric material and has been utilized as a coating material and adhesive since ancient times.Lacquer films have excellent anti-bacterial,waterproof,heatproof,anti-abrasive and anticorrosive properties.Nowadays,there is no literature about microporous lacquer films.In this paper,microporous films were fabricated from synthesized urushiol-formaldehyde diethylenetriamine polymer (UFDP) by “on-solid surface spreading" method and “on-water spreading" method.This is the first report of the two methods to produce micropatterned thin films from UFDP by water-assisted fabrication.Meanwhile,no blow airflow on polymer surface was used.The comparison of the two methods indicated that microporous films with monolayer can be fabricated by spreading on water but with multilayer by spreading on solid.Furthermore,several influencing factors on the formation of the microporous films and the different morphologies,such as the concentration of the polymer solution and the relative humidity in the atmosphere and the substrates,were investigated.The results showed that water surface as a spreading substrate was suitable to form orderly porous films for such a polymer.The monolayer film with a relative uniform pore size distribution could be formed from the polymer with concentration of 6.0 mg/mL at the relative humidity of 90% and room temperature using a water surface.
- 25
- |
- 14
- |
- 2
发布时间：2021-03-19 - 摘要：Polypropylene (PP)/attapulgite (ATP) nanocomposites with enhanced mechanical properties were prepared by a simple and efficient method of melt blending without adding any bulking agent.ATP was pretreated by emulsion oxidized polyethylene envelop，and then dispersed by strong shear stress.The novel pretreatment method in preparing nanocomposites leads higher mechanical properties than those of PP/untreated ATP nanocomposites and pure PP.The impact strength of the composites was increased by 44%～83%,and the tensile strength was increased by 6%～11%.At the mean time,the flexural strength was increased by 33%～45% and the modulus of flexural was increased by 90%～106%.Scan electron microscope （SEM） results reveal that ATP disperses homogeneously in the PP matrix and mainly exist in the form of anomocytic crystal bundle.The diameter of treated ATP units is in the range of 20～40 nm that is much less than that of untreated ATP which is in the rang of 50～80 nm .X-ray diffraction (XRD) shows that PP exhibits α crystals in the composites，and no crystalline phase transition occurrs as reported in literature.The size of PP crystallites was decreased with the addition of ATP.Dynamic mechanical analysis and the results of differential scanning calorimetry (DSC) reflected that the addition of ATP can increase the crystallization temperature and crystallinity of PP/ATP.It is proved that the addition of ATP also gives nucleation effect.The enhancement of the mechanical properties is mainly contributed by the uniform dispersion of ATP and strong interfacial force of PP/ATP.
- 20
- |
- 15
- |
- 5
发布时间：2021-03-19
Research Bulletin
- Postal code：100190
- Tel：010-62588927 Email：gfzxb@iccas.ac.cn
- Technical support is provided by Beijing Founder electronics co., LTD 京ICP备05002797号-8
京公网安备11010802024621 - It is recommended to read the content of this site in Chrome&IE9+. Please switch to extreme mode in browser 360.
- Cookies We use cookies to help provide and enhance our service and tailor content. By continuing, you agree to the use of cookies.
0