Strain rate and loading modes in DMTA experiments on ethylene/propylene block copolymers

A broad experimental programme using Dynamical–Mechanical Thermal Analysis (DMTA) was carried out on ethylene/propylene block copolymers (EPBC). The samples were subjected to frequency scans to evaluate the dependence of stored modulus on frequency. Tests were conducted on similar samples using different loading modes such as single cantilever, dual cantilever and tension configurations. If the stored modulus is plotted versus the test frequency, a different trend corresponding to each loading mode is obtained. Similar conclusions can be drawn regarding the glass transition temperature. In this work, strain rate, instead of frequency, is used to compare results provided by different loading modes. If the strain rate is used as the reference variable, a unique trend is observed despite the loading modes used to perform the experiment.     

On the association and adsorption behaviour of ethylene oxide/propylene oxide block copolymers in the processes of steel corrosion protection

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation of gold nanosheets using poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers via photoreduction

Gold nanosheets having single crystalline structure were successfully synthesized using the bulk phase mixture of HAuCl₄ and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) block copolymers through the irradiation of a glow lamp for 5 days. When the molar ratio of propylene oxide to ethylene oxide block units in the block copolymer is about 1.75, mostly gold nanosheets were obtained. Gold nanosheets with an average width of 8 and 5 μm were obtained from the when the molar ratio of gold salt to the ethylene oxide units in the block copolymer were 1/80 and 1/160, respectively.     

Mechanical properties of weakly segregated block copolymers Part IV Influence of chain architecture and miscibility on tensile properties of block copolymers

Different types of weakly segregated block copolymers are investigated with respect to the influence of chain architecture and miscibility on tensile properties. Poly(styrene-b-butylmethacrylate) diblock copolymers (PS-b-PBMA) as well as poly(butylmethacrylate-b-polystyrene-b-butylmethacrylate) triblock copolymers (PBMA-b-PS-b-PBMA) show synergistic effects on tensile properties. The triblock copolymers show a higher tensile strength and stiffness compared to that of the diblock copolymers. In addition, the triblock copolymers exhibit a larger composition range for which the tensile strength exceeds that of the respective homopolymers. In order to investigate the influence of block miscibility on tensile properties, poly(methylmethacrylate-b-butylmethacrylate) diblock copolymers (PMMA-b-PBMA) are compared with PS-b-PBMA diblock copolymers.     

Control of the structure and properties of barium sulphate-filled blends of polypropylene and ethylene propylene copolymers

The structure and properties of polypropylene (PP) and ethylene propylene copolymer (EPR) blends filled with BaSO₄ have been investigated. The aspect of structure control concerned was the separate dispersion of filler and rubber in the PP matrix or encapsulation of the filler in the rubber phase. The former structure prevails in the PP/EPR/BaSO₄ systems, and addition of maleic anhydride-grafted polypropylene (MAPP) enhances the adhesion between the PP matrix and the filler. Encapsulation of the filler particles into the elastomer takes place when maleated EPR-rubber (EPMA) is used, and the encapsulated structure prevails even under the severe shearing conditions of injection molding. The improved matrix/filler adhesion resulted in increased yield stress and tensile strength, but decreased impact resistance. The particle size of the filler proved to be a crucial factor; below a certain particle size aggregation becomes a dominating factor. Extensive aggregation leads to the deterioration of all mechanical properties, especially to decreased impact strength.     

Heparin-containing block copolymers

Newly synthesized heparin-containing block copolymers, consisting of a hydrophobic block of polystyrene (PS), a hydrophilic spacer-block of poly (ethylene oxide) (PEO) and covalently bonded heparin (Hep) as bioactive block, were coated either onto glass, poly (dimethylsiloxane), polyurethane or PS substrates. Coated surfaces were characterized by determination of the surface-bound heparin activity, adsorption of AT III, plasma recalcification time assays, adhesion of platelets and by an ex vivo rabbit A-A shunt model.It was demonstrated that heparin was available at the surface of all heparin-bound surfaces to interact with AT III and thrombin and to prevent the formation of clots. The maximum immobilized heparin activity was found to be 5.5×10^-3 U cm^-2. Coated surfaces showed a significant prolongation of the plasma reclacification times as compared to control surfaces, due to surface-immobilized heparin. The platelet adhesion demonstrated that platelets reacted only minimally with the heparin-containing block copolymers in the test system and that the heparin-containing block copolymers seemed to passify the surface as compared to control surfaces. In the ex vivo A-A shunt experiments, which were carried out under low flow and low shear conditions, the heparin-containing block copolymers exhibited prolonged occlusion times, indicating the ability of the heparin-containing block copolymers to reduce thrombus formation at the surface.     

Heparin-containing block copolymers

Newly synthesized heparin-containing block copolymers, consisting of a hydrophobic block of polystyrene (PS), a hydrophilic spacer-block of poly(ethylene oxide) (PEO) and covalently bound heparin (Hep) as bioactive block, were coated on aluminium, glass, polydimethylsiloxane (PDMS), PS or Biomer substrates. Surfaces of coated materials were characterized by transmission electron microscopy (TEM), contact angle measurements and X-ray photoelectron spectroscopy for chemical analysis (XPS). It was demonstrated by TEM that thin films of PS-PEO and PS-PEO-Hep block copolymers consisted of heterogeneous microphase separated structures. Using sessile-drop and Wilhelmy plate dynamic contact angle measurements, insight was provided into the hydrophilicity of the surfaces of the coatings. Measurements with hydrated coatings of PS-PEO and PS-PEO-Hep block copolymers revealed that the surfaces became more hydrophilic during immersion in water, due to relaxation/reorientation, or swelling of PEO or PEO-Hep domains, respectively. XPS results for PS, PEO, heparin and PS-PEO as powder agreed well with qualitative and quantitative predictions. XPS results for films of PS-PEO and PS-PEO-Hep block copolymers showed enrichments of PEO in the top layers of the coatings. This effect was more pronounced for hydrated surfaces. Only small amounts of heparin were detected at the surface of coatings of PS-PEO-Hep block copolymers.     

Diffusion of block copolymers

Block copolymers have been attracting the attention of a great number of scientists and engineers with their beautiful ordered structures on a nanometer scale. Repulsion between dissimilar blocks of block copolymers drives micro-phase separation on the length scale—the radius of gyration of the block copolymer chains. Due to the presence of such nano-domains, the diffusion of block copolymers in the melt is significantly reduced in the direction perpendicular to the interface between the domains. In this direction, block copolymer chains diffuse by an activated hopping mechanism in which the shorter block is pulled out from its domain into the majority domain. Consequently, in this direction the diffusion coefficients of block copolymers decrease exponentially with the activation energy of the hopping process χN_sk_BT, where χ is the Flory parameter, N_s is the degree of polymerization of the shorter block, k_B is Boltzmann's constant and T is temperature. The diffusion along the domain interface is less restricted by the presence of domains. The interface diffusion coefficient depends on the degree of segregation and presence of entanglements. Experiments, theories and simulations of block copolymer diffusion in ordered structures are reviewed.     

Equations of state for ethylene and propylene

Equations of state for ethylene and propylene are given, representing the whole experimentally determined region up to 50 MPa. The twenty adjustable coefficients of the equation of state, a modified Benedict-Webb-Rubin equation of state, have been determined using recent experimental data and considering the thermodynamic equilibrium conditions for the co-existing liquid and vapour phases. The results of the equations of state are compared with experimental data.     

Photoinduced ordering of block copolymers

Photoinduced ordering of disordered block copolymers (BCPs) would provide an on-demand, nonintrusive route for formation of well-ordered nanostructures in arbitrarily defined regions of an otherwise disordered material. Here we achieve this objective using a rapid and simple approach in which photoconversion of an additive blended with the BCP introduces strong interactions between the additive and one of the chain segments and induces strong order in the BCP blend. The strategy is generally applicable to block copolymers containing chain segments capable of hydrogen bonding with the additive.     

Fabrication of microchannel structures in fluorinated ethylene propylene

A new technique for fabrication of channel structures with diameters down to 13 microm in fluorinated ethylene propylene (also known as poly(tetrafluoroethylene-co-hexafluoropropylene), FEP) is described. The technique is based on the unique property of a dual-layer fluoropolymer tubing consisting of an outer layer of poly(tetrafluoroethylene) (PTFE) and an inner layer of FEP. When heated (>350 degrees C), the outer PTFE layer shrinks while the inner FEP layer melts, resulting in filling of all empty space inside the tubing with FEP. The channel structures are formed using tungsten wires as templates that are pulled out after completion of the shrinking and melting process. While several analytical devices have been reproducibly prepared and shown to function, this report describes a single example. A microreactor coupled to an electrochemical flow cell detects the biuret complex of the natively electroinactive peptide des-Tyr-Leu-enkephalin.     

聚四氟乙烯改性三元乙丙橡胶的性能

采用混炼后硫化的方法制备聚四氟乙烯(PTFE)及纳米二氧化硅(Si O2)改性的三元乙丙橡胶(EPDM)。扫描电镜、红外光谱等表明PTFE与EPDM具有较好的相容性;差示扫描量热法DSC测试表明,复合物具有唯一的玻璃化转变温度;当PTFE加入量为5份时,PTFE与EPDM具有较好的相容性,此时EPDM-PTFE的力学性能达到最高,其抗拉强度、断裂伸长率、硬度和撕裂强度分别为22. 42 MPa、588. 91%、82. 0°和49. 60 k N/m;热重分析和老化实验表明,经PTFE改性后,其耐老化性和耐热性能均有提高;添加5份纳米Si O2后,EPDM的力学性能也得到显著提高。     

Influence of poly(ethylene glycol) block length on the adsorption of thermoresponsive copolymers onto gold surfaces

The adsorption of a series of four poly(N-isopropylacrylamide)-based copolymers composed of a hydrophilic block of methoxy poly(ethylene glycol) (MPEG) with a variable length and a PNIPAAM block of fixed size (MPEG _n -b-PNIPAAM₇₁) onto flat and spherical citrate-coated gold surfaces has been investigated. The adsorption onto planar surfaces was studied by means of the quartz crystal microbalance with dissipation monitoring, whereas polymer adsorption onto gold nanoparticles was examined using dynamic light scattering and visible spectroscopy. Experiments were performed with two different concentrations of polymer in bulk solution, namely 0.05 and 0.0005 wt%. The influence of the MPEG length on the thickness of the adsorbed layer on the nanoparticles, and the adsorbed mass onto the planar surfaces were recorded at different temperatures.     

端氨基聚乙二醇-聚乳酸嵌段共聚物的合成及表征

以聚乙二醇为原料,采用四步反应,合成了二碳酸二叔丁酯单保护的氨基聚乙二醇(BOC-PEG-NH2);并以DOe-PEG-NH2为引发剂,引发丙交酯开环聚合,得到了叔丁氧基酰胺基聚乙二醇-聚乳酸嵌段共聚物(BOC-PEG-PLA).在三氟乙酸二氯甲烷溶液中,脱去保护基团,得到了端氨基聚乙二醇-聚乳酸嵌段共聚物(NH2-PEG-PLA).采用核磁共振氢谱(1H-NMR)、紫外光度仪(UV)表征各聚合物的结构,由凝胶色谱仪(GPC)测定嵌段共聚物的分子量以及分子量分布.结果表明:合成的氨基引发在无催化剂条件下能够引发丙交酯开环聚合,制得分子量高、分子量分布窄的双亲性共聚物.通过三氟乙酸脱保护得到了端氨基聚乙二醇-一聚乳酸(NH2-PEG-PLA),且对分子量没有影响.     

Computer generated phase diagrams for ethylene and propylene

A method which uses computer graphics to construct pictorial views of three-dimensional thermodynamic phase diagrams is demonstrated. Pressure-volume-temperature diagrams are presented for ethylene and propylene so that quantitative comparisons can be made between the phase surfaces representing the ideal gas law, the Redlich-Kwong equation and a highly accurate, 20-constant equation of state proposed by Bender. Pictorial views of enthalpy-entropy-pressure diagrams for ethylene based solely on P-V-T relations and ideal gas heat capacities are also shown along with their Mollier projections. Interesting comparisons that confirm our understanding of equations of state are made with H-S-P diagrams that represent the properties of an ideal gas in contrast to those of a Redlich-Kwong fluid. Reference is made to earlier papers that describe the computer graphics algorithms in detail.