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A physical model of series of the conductivity on chain and the interchain conductivitybetween chains is proposed to explain enhanced conductivity of stretched conducting polymers.This model suggests that the enhanced conductivity for stretched conducting polymers might bedue to increasing of the interchain conductivity between chains along the elongation direction afterdrawing processes if the conductivity on chain is assumed much larger than that of the interchainconductivity between chains. According to this model, it is expected that the temperaturedependence of conductivity measured by four-probe method for stretched conducting polymers iscontrolled by a variation of the interchain conductivity between chains with temperature, whichcan be used to explain that a metallic temperature dependence of conductivity for stretchedconducting polymers is not observed although the conductivity along the elongation direction isenhanced by two or three orders of magnitude. 相似文献
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In this paper, the microstructure change of one step-draw PET fiber has been studied byvarious methods, such as, Laser Raman Microscope, Wide-angle X-ray, Density-gradient andPolarizing Microscope. The computer has been used to resolve overlapped bands in the Ramanspectra. Then the band changes have been correlated with trans, gauche and stressed trans-conformations indicated by a conformational index. Based on these indices, the relationshipbetween the conformation change of glycol units in the fiber structure and the macromechanicalproperties of fiber is expounded. 相似文献
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COMPATIBILITY STUDIES ON POLYMER/WAX AND POLYMER/RESIN-ASPHALTENE BY VISCOMETRY AND PHOTOMICROGRAPHY
The compatibility of mixtures of polymeric pour point depressants, i.e. poly(ethylene-co-vinylacetate) (EVA), poly (EVA-graft-octadecylacrylate) (EVA-g-POA ), poly (ethylene-co-octadecylacrylate) (EOA) and poly(ethylene oxide-co-propylene oxide) (EO-co-PO) withwax or resin-asphaltene from crude oil have been studied by means of dilute-solution vis-cometry. It was found that each mixture pair is incompatible, but the degrees of incompati-bility are quite different, which are in good agreement with the results from photomicrog-raphy. 相似文献
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Polyethers could form hydroperoxide under air-oxidation or photo-oxidation in the presence of H_2O_2. The scission of ether linkage induced by moderate oxidation was prevented by controlling the reaction time and hydroperoxide concentration. The oxidation rate was affected by the end groups of polyethers. The decreasing order of oxidation rate for various poly(tetramethylene ether) glycol derivatives having different end groups are as follows: poly(tetramethylene ether) glycol (PTMG)>poly(tetramethylene ether)acetate (PTMGAC) >poly(tetramethylene ether) phenyl carbamate (PTMGPC). The urethane end groups in PTMGPC increase the resistance toward oxidation. Polyether hydroperoxide reacts with ferrous ion or N,N-dimethyl toluidine (DMT) to form polymericoxy radical which then initiates the graft copolymerization of vinyl monomers at low temperature, and was devoid of homopolymerization. The copolymer after separation and purification was proved to be a graft one by IR analysis and elemental analysis. 相似文献
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The epoxy resin modified by liquid chloroprene-hydroxyethylmethacrylate copolymer (CP-HEMA) is a new kind of structural adhesives with good mechanical properties. By changing its mole-cular structure, it may also have such desirable properties as retardation of combustion, enduringweather aging, inert oils and chemicals. A series of the thermosets of the epoxy resin modifiedby CP-HEMA used as a toughener were prepared. The effects of CP-HEMA content, catalyst con-tent and curing temperature on the mechanical properties of modified epoxy resin system were studied.The thermal weight-loss curves were examined. The two-phase morphology was observed and dis-cussed. 相似文献
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Zheng-ping Fang Gen-lin Wang Guo-ping Cai Cheng-wei Xu Jie Qian Institute of Polymer Composites Zhejiang University Hangzhou China College of Chemical Engineering Zhejiang University of Technology Hangzhou China 《高分子科学》2000,(5):437-441
The morphology of polyvinyl chloride/polystyrene (PVC/PS) blend samples with different mass ratios, preparedby means of solution casting and melt mixing, have been successfully examined by electron microprobe analysis (EMP). Thisexperiment was performed in a scanning electron microscope attached to an energy dispersive X-ray analyzer. Differentialscanning calorimetry was also used to investigate the phase separation of the blends. The results show that PVC and PS areincompatible and the blends have sea-islands phase structures. Blends prepared via melt mixing have finer phase-dispersionthan those prepared via solution casting. 相似文献
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Ethyl-cyanoethyl cellulose [(E-CE)C]/cross-linked polyacrylic acid [PAA] molecular compositeswith cholesteric order were prepared. It was found that the macromolecular cholesteric structure was changedwith the swelling of PAA in the composites. The selective reflection of the cholesteric phase shifted to thelonger wavelength and the X-ray diffraction angle shifted to the high angle direction during swelling, whichsuggested that the cholesteric pitch and the number of the layers of ordered (E-CE)C chains in the cholestericphase were increased. 相似文献
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INTRODUCTIONMacromolecular gelatin is principally derived from type collagen. Gelatin hydrolyzate can be prepared frommacromolecular gelatin by hydrolytic reaction with acid, alkali, heating or enzyme.The gelatin hydrolyzate maintains most of the inherent physical and chemical characteristics ofmacromolecular gelatin and also acquires some new ones by taking advantage of the lowering of the molecularweight. With the advancement of science and technology, the application of gelatin hydroly… 相似文献
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STUDIES ON THE NATURE OF THE MACROMOLECULAR CONDENSED STATE OF "NASCENT" ULTRA HIGH MOLAR MASS POLYETHYLENE* 总被引:1,自引:0,他引:1
Zhong-yong Fan Qiang Lan Hai-shah Bu Li-heng Wu Lin Sun Ren-yuan Qian Shou-xi Chen Yong-feng Men Bing-zheng Jiang 《高分子科学》2001,(1):25-31
Ultra high molar mass polyethylene (UITPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC,effect ofannealing the recrystallized specimen at 120~I30℃, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220℃, possibly higher than 300℃, the exact temperature is however not sure because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120~130℃. 相似文献
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The emulsion copolymerization of vinylidene chloride (VDC) with methyl-methacrylate(MMA) and acrylonitrile (AN) was carried out by batch, seeded batch and semicontinuous pro-cesses,respectively. Significant differences were found in the physical and mechanical propertiesof the latexes and films, depending on the methods of monomer feeding. The results both intheory and experiments demonstrated that the copolymer composition and the length of the VDC sequences in the copolymer could be controlled by the modes of monomer feeding process. 相似文献
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Macroreticular bead PAN/PVC IPN resins with cyano and chloro groups were synthesized by interpenetrating polymerization of acrylonitrile, or acrylonitrile and divinylbenzene into a macroporous polyvinyl chloride bead. The composition and structure of the bead IPN resins have been investigated by means of FT-IR, NMR, SEM, mercury porosimetry and elemental analysis. During the process of interpenetrating polymerization, the chain propagation obeys Bernoullian statistical law, and no grafting polymerization has been observed. The content of cyano group in the resulting IPN resins can be adjusted by the amount of acrylonitrile added. The morphology of the IPN resins basically resembles that of the polyvinyl chloride bead, whereas the pore structures vary to a certain degree 相似文献
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INTRODUCTIONIn recent years, polymer/clay nanocomposites have attracted great interest from researchers since they frequentlyexhibit unexpected hybrid properties synergistically derived from the two components. Compared to their microcounterparts and the pristine polymer matrix, polymer/clay nanocomposites exhibit improved tensile strength andmodulus, decreased thermal expansion coefficient, decreased gas permeability, increased swelling resistance,enhanced ion conductivity, and reduced fl… 相似文献
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Polyvinyl alcohol coated magnetic particles (PVA ferrofluids) have been synthesized by chemical co-precipitationof Fe(Ⅱ)/Fe(Ⅲ) salts in 1.5 mol/L NH_4OH solution at 70℃ in the presence of PVA. The resultant colloidal particles havecore-shell structures, in which the iron oxide crystallites form the cores and PVA chains form the shells. The hydrodynamicdiameter of the colloidal particles is in the range of 108 to 155 nm, which increases with increasing PVA concentration from5 wt% to 20 wt%. The size of the magnetic cores is ca. 5~10 nm, which is relatively independent of PVA concentration.Under transmission electron microscopic (TEM) examination, the magnetic cores exhibit somewhat irregular shapes varyingfrom spherical, oval, to cubic. Magnetometry measurement revealed that the PVA coated magnetic particles aresuperparamagnetic. The saturation magnetization of 5 wt% and 20 wt% PVA ferrofluids at 300 K is 54 and 49 emu/g.respectively. All the PVA ferrofluids exhibited excellent colloidal stability in pure water and phosphate buffer saline (PBS,pH=7.4). The ferrofluids can remain stable in above solutions for more than three months at 4℃. 相似文献
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The effects of inter facial modifier on the mechanical, dynamic mechanical properties andcrystallization behavior of the polyethylene composites were investigated in the present paper.It was found that the interfacial modifer significantly improved the mechanical properties,influenced the dynamic mechanical spectra and slightly changed the crystallization behavior.The results showed that the interfacial modifier changed the dispersion state of dispersedphase of the composites, resulting in different phase structure, which was the major reasonIeading to different mechanical and crystallization properties. 相似文献
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Barium titanate (BaTiO3) powders with particle sizes of 30~50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wt % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide. 相似文献
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Critical concentrations of lyotropic liquid crystalline ethylcellulose in more than tensolvents were determined using both Abbe refractometer and polarized microscopy. Criti-cal concentration C_(crit) of forming liquid crystal phase decreased with increasing solubilityparameter δ of solvent until approaching the δ of polymer. Although the alcohols usedas solvents had the same variation rule, the critical concentration values of their solutionswere much higher, due to their excessive large hydrogen bond component of δ. The experi-ments of using mixed solvents which showed good linear relation between C_(crit) and δ alsoproved this rule. A technique of Transmission Optical Analysis was first used to estimatethe concentration dependence of critical phase transition temperature T_(crit) of EC, and aT-C phase diagram could be drawn. 相似文献
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The study of nanosecond dynamics of macromolecules with the lumines-cent methods make it possible to investigate the formation and functioning of polymericcomplexes, polymeric conjugates and macromolecular metal complexes, which are widelyused for solving many practical tasks. The nanosecond dynamics of macromolecules are ahighly sensitive indicator of interpolymer complexes (IPC) formation. It enables us to solvethe problems of studying IPC formation and stability and to investigate the interpolymerreactions of exchange and substitution. The investigation of changes in the rotational mo-bility of globular protein molecules as a whole makes it possible to determine the complexcomposition and its stability, and to control the course of polymer-protein conjugate forma-tion reaction. The nanosecond dynamics of polymers interacting with surfacants' ions (S)are the sensitive indicator of the S-polymer complex formation. A method for determin-ing the equilibrium constants of the S-polymer complex formation was developed on thebasis of the study of polymer chains mobility. It is established that nanosecond dynamicsinfluences the course of chemical reactions in polymer chains. Moreover, the marked effectof the nanosecond dynamics is also revealed in the study of photophysical processes (theformation of excimers and energy migration of electron excitation) in polymers with pho-toactive groups. It was found that the efficiency of both processes increases with increasingthe mobility of side chains, the carriers of photoactive groups. 相似文献
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Polysiloxane-polystyrene composite latexes were prepared by two-stage emulsionpolymerization. Polymerization of styrene in swollen polysiloxane latex particles were studied.Formation of simple polystyrene particle in the 2nd-stage polymerization depends on the particlesize of the lst-stage latex and the polymerization temperature. Polystyrene domains in thevulcanizates reinforce the silicone rubbers effectively. 相似文献