摘要:The evolution and the origin of "solid-like state" in molten polymer/clay nanocomposites are studied. Using polypropylene/clay hybrid (PPCH) with sufficient maleic anhydride modified PP (PP-MA) as compatibilizer, well exfoliation yet solid-like state was achieved after annealing in molten state. Comprehensive linear viscoelasticity and non-linear rheological behaviors together with WAXD and TEM are studied on PPCH at various dispersion stages focusing on time,temperature and deformation dependencies of the "solid-like" state in molten nanocomposites. Based on these, it is revealed that the solid-structure is developed gradually along with annealing through the stages of inter-layer expansion by PP-MA,the diffusion and association of exfoliated silicate platelets, the formation of band/chain structure and, finally, a percolated clay associated network, which is responsible for the melt rigidity or solid-like state. The network will be broken down by melt frozen/crystallization and weakened at large shear or strong flow and, even more surprisingly, may be disrupted by using trace amount of silane coupling agent which may block the edge interaction of platelets. The solid-like structure causes characteristic non-linear rheological behaviors, e.g. residual stress after step shear, abnormal huge stress overshoots in step flows and, most remarkably, the negative first normal stress functions in steady shear or step flows. The rheological and structural arguments challenge the existing models of strengthened entangled polymer network by tethered polymer chains connecting clay particles or by chains in confined melts or frictional interaction among tactoids. A scheme of percolated networking of associated clay platelets, which may in band form of edge connecting exfoliated platelets, is suggested to explain previous experimental results.
摘要:Polymer chain coils with entanglement is a crucial scale of structures in polymer materials since their relaxation times are matching practical processing times. Based on the phenomenological model of polymer chain coils and a new finite element approach, we have designed a computer software including solver, pre- and post-processing modules, and developed a digital analysis technology for the morphology of polymer chain coils in flow fields (DAMPC). Using this technology we may simulate the morphology development of chain coils in various flow fields, such as simple shear flow, elongational flow,and any complex flow at transient or steady state. The applications made up to now show that the software predictions are comparable with experimental results.
摘要:Polyolefins that bear a chiral side chain (typically an isobutyl group) experience a so-called macromolecular amplification of chirality: the chiral side-chain induces a slight preference for either tg or tg- main chain conformation. This slight conformational bias is amplified cooperatively along the chain, and results in preferred chirality of the main chain helical conformations. As a result, these polymers display a liquid-crystal (LC) phase both in solution and, in the melt as a transient phase on the way to crystallization. The existence of two processes (melt-LC and LC-crystal transitions) results in unconventional behaviors that were first analyzed by Pino and collaborators back in 1975. These polymers also offer a means to test the structural consequences of recently introduced crystallization schemes. These schemes postulate the formation of a transient liquid-crystal phase as a general scheme for polymer crystallization.
摘要:The time evolution of oxygen plasma treated polystyrene (PS) surfaces was investigated upon storing them in the air under controlled humidity conditions. The methods of water contact angle, X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, and atomic force microscopy (AFM) were used to infer the surface properties and structure. Chemical groups containing oxygen were formed on the PS surface with the plasma treatment,demonstrated by water contact angle and XPS. The surface polarity decayed markedly on time, as assessed by steady increase in the water contact angle as a function of storage time, from zero to around 60°. The observed decay is interpreted as arising from surface rearrangement processes to burying polar groups away from the uppermost layer of the surfaces, which is in contact with air. On the other hand, XPS results show that the chemical composition in the first 3 nm surface layer is unaffected by the surface aging, and the depth profile of oxygen is essentially the same with time. A possible change of PS surface roughness was examined by AFM, and it showed that the increase of water contact angle during surface aging could not be attributed to surface roughness. Thus, it is concluded that surface aging is attributable to surface reorganization and the motion of oxygen containing groups is confined within the XPS probing depth. SFG spectroscopy, which is intrinsically interface-specific, was used to detect the chemical structure of PS surface at the molecular level after various aging times.The results are interpreted as follows. During the aging of the plasma treated PS surfaces, the oxygen containing groups undergo reorientation processes toward the polymer bulk and/or parallel to the surface, while the CH2 moiety stands up on the PS surface. Our results indicate that the surface configuration changes do not require large length scale segmental motions or migration of macromolecules. Motions that are responsible for surface configuration changes could be relatively small rotational motions. The aging behaviors under different relative humidity conditions were shown to be similar from 18% to 91%, whereas the kinetics of surface polarity decays were faster in higher relative humidity. Here, the surface rearrangement of polystyrene films that were previously treated by oxygen plasma and aged, and was investigated in terms of contact angle after the water immersion. The contact angles of the water-immersed samples were found to change and approach the initial values before the immersion asymptotically.
摘要:Composite polyurethane (PU)-SiO2 hollow fiber membranes were successfully prepared via optimizing the technique of dry-jet wet spinning, and their pressure-responsibilities were confirmed by the relationships of pure water fluxtransmembrane pressure (PWF-TP) for the first time. The origin for this phenomenon was analyzed on the basis of membrane structure and material characteristics. The effects of SiO2 content on the structure and properties of membrane were investigated. The experimental results indicated that SiO2 in membrane created a great many interfacial micro-voids and played an important role in pressure-responsibility, PWF and rejection of membrane: with the increase of SiO2 content, the ability of membrane recovery weakened, PWF increased, and rejection decreased slightly.
摘要:The isothermal crystallizations of three kinds of commercial isotactic polypropylene have been studied by DSC and rheometric experiments, in a range of temperatures where the rate of crystallization is moderate. As the crystallization proceeds, volume contraction induces tensile force upon the parallel plates. The tensile force relaxed quickly in liquid states,but after a critical amount of the relative crystallinity, it starts to accumulate in the static test, that is, with the motionless parallel plates. A new method to determine the liquid-solid transition by the static tensile force is proposed and compared with two dynamic methods of detecting liquid-solid transition, that is, the power-law modulus theory and the yield modulus model. The tensile force method predicted considerably earlier transition than the dynamic methods, and the corresponding DSC data indicate relative crystallinity of larger than 0.2 at the transition times. The limitation of dynamic methods and other possible errors have been analyzed. While the dynamic methods are suitable for slow crystallization, the tensile force method is more appropriate for the crystallization of moderate rates. Moreover, it has the advantage of almost not disturbing the crystallizing materials before the transition.
摘要:Grafting of poly(methyl methacrylate) from narrow disperse polymer particles by surface-initiated atom transfer radical polymerization (ATRP) was investigated. Polydivinylbenzene (PDVB) particles were prepared by dispersion polymerization with poly(N-vinyl pyrrolidone) (PVP) as the stabilizer. Chloromethylated PDVB was used as initiating core sites for subsequent ATRP of methyl methacrylate with CuBr/bpy as catalyst system. It was found that poly(methyl methacrylate) was grafted not only from the particle surfaces but also from within a thin shell layer, leading to particles size increases from 2.38-3.00 μm with a core-shell structure particles. The grafted core-shell particles were characterized with FTIR, SEM, DSC.
摘要:The surface of nano-TiO2 was encapsulated with hydroxyl-propyl-methyl cellulose (HPMC), and then cografted with acrylates. Conditions of absorbing and grafting have been studied. Modified nano-TiO2 particles were characterized by FT-IR spectra, TEM and TG analysis. It was convinced from FT-IR studies that both methyl methacrylate (MMA) and butylmethacrylate (BMA) were co-grafted onto the surface of nano-TiO2 particles. TEM images show that the surface of nanoTiO2 particles was successfully modified by a thick layer of film-like polymer. TG results demonstrate that the decomposition temperature of HPMC-g-PMMA/PBMA, which has been grafted onto the surface of nano-TiO2, is 56.9 K higher than that of HPMC-g-PMMA/PBMA.
摘要:A side-on liquid crystalline monomer, 2,5-bis[(4-hexyloxyphenyl)oxycarbonyl]styrene) (HPCS), was successfully polymerized via atom transfer radical polymerization (ATRP). The polymerization was catalyzed by CuBr/PMDETA in chlorobenzene at 90℃ with (1-bromoethyl)benzene as the initiator. The polymers have narrow MWD. It is the second example of mesogen-jacketed liquid crystalline polymer (MJLCP) prepared by ATRP.
摘要:A kind of core(SBR)-shell(PS) particles was synthesized by using SBR latex and grafting with St under gamma irradiation. The influences of absorbed dose and dose rate on the grafting yield of PS on SBR seed latex have been investigated. Results show there was a transition layer which contained the SBR/PS graft copolymer between the SBR core and PS shell. Dynamic laser scattering (DLS) and differential scanning calorimetry (DSC) results confirm the existence of grafted polystyrene, and transmission electron microscope (TEM) observation verifies the core-shell structure of SBR-g-PS latex. Such SBR/PS core-shell latex could be processed easily to ultrafine rubber powders by using spray drying and expected to be used as an impact modifier for PS.
摘要:Fe(Ⅱ) pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane (MMAO) as catalysts were employed for the polymerization of butyl methacrylate (BMA). Polymer yields, catalytic activities and molecular weights as well as molecular weight distributions of BMA can be controlled over a wide range by varying the reaction parameters such as cocatalyst, A1/Fe molar ratio, monomer/catalyst molar ratio, monomer concentration and reaction yield could reach 99.1% under optimum condition.
摘要:Swelling property of acrylamide hydrogels, prepared from aqueous solutions of acrylamide monomer having concentrations in the range of 10-60 wt% by γ-ray irradiation method using a Co-60 gamma radiation source at doses ranging 1-30.0 kGy, has been investigated under various swelling media. These swelling media were basically solvents (solutions), produced by dissolving methanol, ethanol, glucose, sucrose, sodium chloride and sodium persulfate individually with distilled water, and solutions prepared with phs = 3, 7 and 10. The investigation was performed in order to observe the effect of these solvents and phs as well as the influence of monomer concentrations, radiation doses and times on swelling behavior of hydrogels. Swelling values were found higher for hydrogels prepared with lower monomer concentrations (ca.20 wt%) and radiation doses (ca. 5 kGy) and showed a leveling off tendency within 24 h. The glucose solvent and the buffer solution of pH = 10 revealed significant increase of swelling of hydrogels as compared to other solutions. Results are explained based on crosslinking density in hydrogel, polymer-solvent/polymer-polymer interactions in solutions,permeability of molecules in solutions and ionization capacity of hydrogel in pH.
摘要:Small fixed aggregates of a poly(ethylene oxide)-block-polybutadiene diblock copolymer (PEO-b-PB) in THF solution were obtained by adding a selective solvent for PB blocks, followed by cross-linking the PB shells. The morphologies of the nanostructured particles with a cross-linked shell were investigated by atomic force microscopy and transmission electron microscopy. The average behaviors of the PEO crystallization and melting confined within the nanostructured particles were studied by using differential scanning calorimetry experiments. For the deeply cross-linked sample (SCL-l), the crystallization of the PEO blocks was fully confined. The individual nanoparticles only crystallized at very low crystallization temperatures (TcS), wherein the homogenous primary nucleation determined the overall crystallization rate. For the lightly cross-linked sample (SCL-2), the confinement effect was Tc dependent. At Tc ≤ 42℃, the crystallization and melting behaviors of SCL-2 were similar to those of the pure PEO-b-PB diblock copolymer. At Tc > 42℃,SCL-2 could form PEO lamellae thicker than those of the pure PEO-b-PB crystallized at the same Tc.
摘要:Intermittent shear flow including start-up flow and small oscillatory amplitude time sweep or stress relaxation after cessation of shear flow was used to study the rheological behavior and internal structure of thermotropic liquid crystalline polymer (TLCP). There are two kinds of intermittent shear flow: all start-up flows are in the same direction (intermittent flow forward: IFF) and start-up flows change their directions alternately (intermittent flow reversal: IFR). The results show that the stress of start-up flow of IFF and IFR in the test process is not superposed, indicating different changes of internal structure of thermotropic LCP (TLCP). Two main factors affect structure changes in the experimental time scale. One relates to long-term texture relaxation process, the other is an interchain reaction that becomes important after 30 min. The two factors raise the stress of IFF, but express complex effects for the stress of IFR. The latter factor becomes very important at long time annealing process. The relaxation behavior was also studied by the application of wide range relaxation spectrum calculated from the combined dynamic modulus, which gave three characteristic relaxation times (0.3, 10 and 600 s)ascribable to the relaxations of less-phase orientation, domain orientation, and domain deformation, respectively. The result also shows that the domain coalescence (texture relaxation), a long relaxation time, is a much slow process and lasts beyond 2400 s of the test time.
摘要:Grafting of polystyrene with narrowly dispersed polymer microspheres through surface-initiated atom transfer radical polymerization (ATRP) was investigated. Polydivinylbenzene (PDVB) microspheres wereprepared by dispersion polymerization with poly(N-vinyl pyrrolidone) (PVP) as stabilizer. The surfaces of PDVB microspheres were chloromethylated by chloromethyl methyl ether in the presence of zinc chloride as catalyst to form chloromethylbenzene initiating core sites for subsequent ATRP grafting of styrene using CuC1/bpy as catalytic system. Polystyrene was found to be grafted not only from the particle surfaces but also from within a thin shell layer, resulting in the formation of particles size increased from 2.38-2.58 μm, which can further grow to 2.93 μm during secondary grafting polymerization of styrene. This demonstrates that grafting polymerization proceeds through a typical ATRP procedure with living nature. All of the prepared microspheres have narrow particle size distribution with coefficient of variation around 10%.
摘要:Catalytic properties of polymer-stabilized colloidal metal nanoparticles synthesized by microwave irradiation were studied in the selective hydrogenation of unsaturated aldehydes, o-chloronitrobenzene and the hydrogenation of alkenes. The results show that nanosized metal particles synthesized by microwave irradiation have similar catalytic performance in selective hydrogenation of unsaturated aldehydes, better selectivity to o-chloroaniline in hydrogenation of o-chloronitrobenzene and higher catalytic activities in hydrogenation of alkenes, compared with metal clusters prepared by conventional heating. The same apparent activation energy (Ea = 29 kJ mol-1) for hydrogenation of 1-heptene catalyzed with platinum nanoparticles prepared by both heating modes implied that the reaction followed the same mechanism.
摘要:Photoinitiated inverse emulsion polymerization of sodium acrylate (AANa) in kerosene was carried out at room or lower temperature, using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as the initiator. Kinetic investigations indicated that the polymerization could be completed in about 30 min and produce polymer with high molecular weight (106~107). It was found that monomer droplets are the main sites for the polymerization (nucleation). With the increase of DMPA concentration, polymerization rate (Rp) reaches a maximum value while molecular weight of the produced polymer has an adverse result, but the dependence of Rp on incident light intensity is similar. Influences of other parameters such as monomer concentration, emulsifier content and reaction temperature, etc. were also studied. At lower pH values of water phase, Rp depends strongly on the pH due to the electrostatic interaction between the ionized radicals and the monomer. At higher pH, Rp shows a slight dependence on pH.
摘要:The effect of pan-milling on morphological structure, processability and properties of PVC was studied through SEM, FTIR, granulometer, GPC and mechanical properties test in the hope of gaining ease in operation, needless of plasticizers, a clean and efficient route for improving the processability of PVC through stress-induced reactions,fulfilling the idea of 'plasticizing PVC by itself'. The experimental results show that during pan-milling at ambient temperature, within 2-3 min, the microcrystalline structure of PVC becomes indistinct, the grain size of PVC is reduced from 130-160 μm to 1-50 μm the molecular weight of PVC is slightly decreased, the variation of molecular weight distribution is indistinct, the plasticizing time and torque at balance drop a great deal from 71-132 s to 31-33 s and from 18.2-22.1 Nm to 14.7-18.4 Nm, respectively, the processability of PVC is markedly improved, and the mechanical properties get enhanced too.
摘要:A neutral nickel (Ⅱ) catalyst D, { [O-(3-cyclohexyl)(5-Cl)C6H2-ortho-C(H)=N-2,6-C6H3(i-Pr)2]Ni(Ph3P)(Ph)} has been synthesized and characterized by 1H-NMR, FTIR and elemental analysis. The results indicate that Al(i-Bu)3 is an effective cocatalyst for the neutral nickel catalyst. With bis(1,5-cyclooctadiene) nickel(0) [Ni(COD)2] or Al(i-Bu)3 as a cocatalyst, the neutral nickel catalyst D is active for ethylene polymerisation and copolymerisation with polar monomers (tertbutyl 10-undecenoate(BU), methyl 10-undecenoate (MU), allyl alcohol (AA) and 4-penten-1-ol (PO)) under mild conditions.The resulting polymers were characterized by 1H-NMR, FTIR, DSC, and GPC. From the comparative studies, Ni(COD)2 is more active than Al(i-Bu)3 for ethylene homopolymerization, while Al(i-Bu)3 is more effective than Ni(COD)2 for ethylene copolymerisation with polar monomers. The polymerization parameters which affect both the catalytic activity and properties of the resulting polyethylene were investigated in detail. Under the conditions of 20 μmol catalyst D and Ni(COD)2/D = 3(molar ratio) in 30 mL toluene solution at 45℃, 12 × 105 Pa ethylene for 20 min, the polymerization activity reaches as High as7.29×105gPE.(mol.Ni·h)-1and Mηis 7.16×104g.mol-1.For ethylene copolymerization with polar monomers,the effect of comonomer concentrations was examined. As high as 0.97 mol% of MU, 1.06 mol% of BU, 1.04 mol% of AA and 1.37 mol% of PO were incorporated into the polymer, respectively, catalyzed by D/Al(i-Bu)3 system.
摘要:Direct difference methods have been used to solve the simultaneous non-linear partial differential equations for melt spinning without recourse to linearisation or perturbation approximation. The stability of each difference schemes was studied by error analysis using the Taylor series, and by comparison of the results obtained from numerical simulation with the logical value in melt spinning. It is found that computation with 19 digit long double precision has significantly simplified the stability problem of difference equations. Using this method, the precise critical draw ratio of draw resonance in an isothermal and uniform tension spinning of Newtonian fluids can be obtained in between 20.218 and 21.219, a figure consistent with 20.218 which was obtained by a linear perturbation approximation method by Kase and Denn. It thus has paved the way to computation of full information for unsteady melt spinning processes using the difference method.
摘要:The conformational properties and elastic behaviors of protein-like single chains in the process of tensile elongation were investigated by means of Monte Carlo method. The sequences of protein-like single chains contain two types of residues: hydrophobic (H) and hydrophilic (P). The average conformations and thermodynamics statistical properties of protein-like single chains with various elongation ratio λ were calculated. It was found that the mean-square end-to-end distance r increases with elongation ratio,λ. The tensor eigenvalues ratio of : decreases with elongation ratio λ for short (HP)x protein-like polymers, however, the ratio of : increases with elongation ratioλ,especially for long (H)x sequence. Average energy per bond increases with elongation ratioλ, especially for(H)x protein-like single chains. Helmholtz free energy per bond also increases with elongation ratioλ. Elastic force (f), energy contribution to force (fU) and entropy contribution to force (fs) for different protein-like single chains were also calculated.These investigations may provide some insights into elastic behaviors of proteins.
摘要:Lentinan samples, (1→3)-β-D-glucans containing 4.6-15.2 wt% proteins, coded as L-I1, L-I2, L-I3 and L-I4 (L-I)were isolated from four kinds of Lentinus edodes. These glucans were treated with acetone to remove the protein in order to obtain free protein glucans coded as LNP-I1, LNP-I2, LNP-I3 and LNP-I4 (LNP-I). The free-protein polysaccharides were sulfated to give derivatives (S-LNP-I) with degree of substitution (DS) from 0.4-0.8. The structural features and weight- average molecular weight (Mw) of the samples were investigated by using infrared spectroscopy, elemental analysis,13C-NMR, size exclusion chromatography combined with laser light scattering (SEC-LLS) and viscometry. The effects of structure and conformation of the polysaccharides on antitumor activities were assayed in vivo (Sarcoma 180 solid tumors)and in vitro (Sarcoma 180, HL-60, MCF-7 and Vero tumors). The results indicated that the predominant species of the samples L-I and LNP-I in 0.2 mol/L NaCl aqueous solution existed as triple-helical chains with high rigidity and in dimethyl sulfoxide (DMSO) as single-flexible chains. Interestingly, the antitumor activities of LNP-I are lower than those of the native glucans (L-I), whereas their sulfated derivatives have higher inhibition ratio against Sarcoma 180 than LNP-I. The results reveal that the binding of protein, sulfated modification and the triple helix conformation are important factors in the enhancement of the antitumor activities of polysaccharides on the whole.