Self‐Assembling of SBS Block Copolymers as Templates for Conductive Silver Nanocomposites

Novel nanocomposites based on conductive Ag nanoparticles and a self‐assembled polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer were investigated. Good confinement of the nanoparticles into polystyrene microphase was achieved by the addition of DT as surfactant. The polymeric matrix kept its hexagonal order packed cylindrical structure up to 7 wt.‐% content of Ag nanoparticles. An electrostatic force microscopy (EFM) analysis of well‐dispersed metal‐organic hybrid Ag/SBS films was used to characterize the electric behavior of the conductive nanocomposites.

     

两亲扩展型共聚物的合成及中间极性嵌段对乳化性能的影响

采用聚乙二醇单甲醚(Mn=1 900,5 000)分别引发丙交酯和ε-己内酯开环聚合合成了中间嵌段(PLA)聚合度递增的聚乙二醇-聚丙交酯-聚己内酯(MPEG-PLA-PCL)两亲扩展型共聚物和相应的聚乙二醇-聚己内酯(MPEG-PCL)两嵌段共聚物。用FTIR、1HNMR和GPC对产物结构进行了表征,研究了共聚物和常规低分子表面活性剂的乳化性能,探讨了中间极性嵌段的长度对共聚物乳化性能的影响。结果表明,对于甲苯/水体系,共聚物可用于制备稳定的O/W型乳液,且三嵌段共聚物的乳化性能优于低分子表面活性剂;随着引入PLA嵌段聚合度的增加,共聚物的乳化能力呈先增加后减小的趋势;相对于MPEG1900系列共聚物,MPEG5000系列共聚物中需要引入更长的中间嵌段才能获得最佳乳化性能。     

苯乙烯类嵌段共聚物的国内外市场

分析了国内外苯乙烯类嵌段共聚物(SBC)的供需状况，提出了发展我国SBC生产的一些建议。     

Molecular Characterization of Styrene-Butadiene-Styrene Block Copolymers (SBS) by GPC, NMR, and FTIR

Summary This paper deals with the characterization of styrene-butadiene-styrene (SBS) block copolymers at molecular level through different techniques. SBS molecular weight distributions (MWD) were measured by Gel Permeation chromatography (GPC) in tetrahydrofuran (THF) solvent and using a calibration curve based on mono-dispersed polystyrene standards; afterwards, the relative molecular weights obtained by GPC were adjusted using a correction factor based on Mark-Houwink-Sakurada parameters for SBS in THF. Quantitative characterization of polybutadiene (PB) structures in SBS was made by solid-state ¹³C Nuclear Magnetic Resonance (NMR). A novel method using Fourier transform infrared spectroscopy (FTIR) has been developed for characterizing the SBS composition. This method covers the determination of composition in SBS ranging from 20 to 75 wt% of polybutadiene (PB) and was performed based on a FTIR calibration curve, which was prepared using mixtures of polystyrene (PS) and polybutadiene (PB) of known compositions.     

Synthesis and Thermal Characterization of Some Novel ABA Block Copolymers

The synthesis of some novel ABA block copolymers is reported. The block A is a PPO while the block B is a random copoly(aryl ether sulfone), synthesized with three different molecular weights. The block copolymers were obtained by a two step procedure consisting on the functionalization of the random copoly(aryl ether sulfone) followed by a condensation with PPO. Spectroscopic techniques (¹H NMR and ¹³C NMR) were used to characterize the polymers obtained from each step. The NMR data proved the complete conversion of amino groups after the first reaction step and gave some useful insights on the completion of the second step. Copolymer formation is supported by a comparison of the thermal behavior of the block copolymers with respect to the physical blends of the two homopolymers. DSC and DMA analyses showed double glass transitions for the physical blends which could be related to the immiscibility of the two homopolymers, while, in contrast, the block copolymer showed single glass transition. Blends of ABA triblock copolymer/PPO and of ABA triblock/copoly(arylen ether sulfone)s were also prepared. These blends, tested by DSC, showed a good level of compatibility of the ABA copolymer with its singular constituents.

     

Fracture Behaviour of Styrene/Butadiene Block Copolymers having Different Molecular Architecture

The crack toughness behaviour of styrene/butadiene block copolymers of triblock and star architectures was investigated using instrumented Charpy impact testing. In order to evaluate adequately the toughness behaviour of the investigated materials, different concepts of elastic‐plastic mechanics (J‐integral and crack‐tip opening displacement, CTOD concepts) were used. Although the lamellar block copolymers showed a remarkably enhanced ductility in the tensile test than the neat block copolymer having hexagonal PB cylinders in PS matrix, no pronounced difference in crack toughness was found. This behaviour implies that the tensile strain cannot be regarded as the only parameter defining the toughness value. A brittle/tough transition was observed in a lamellar star block copolymer on blending with a linear thermoplastic elastomeric SBS triblock copolymer.

SEM micrograph showing the details of the stable crack propagation region in a binary block copolymer blend.     

Pluronic嵌段共聚物胶束化行为及其胶束增溶

两亲性质的Pluronic嵌段共聚物在合适条件下能自发形成内核很大的稳定胶束 ,其胶束化行为复杂 ,初步的研究深化了对两亲分子自组织机理的认识。实验发现这类胶束具有很强的增溶油溶性物质的能力 ,由于这些分子单体和胶束化行为的特点 ,可望利用这类嵌段共聚物实现在增溶应用场合中的突破。综述Pluronic嵌段共聚物的胶束化行为和胶束增溶规律的当前研究进展     

Synthesis and Characterization of Polystyrene-b-Poly(4-vinyl pyridine) Block Copolymers by Atom Transfer Radical Polymerization

We aimed at the synthesis of well-define PS-b-P4VP by using atom transfer radical polymerization in two-step process. First, polystyrenes with benzyl bromide end group (PS-Br; by ATRP) were prepared as macroinitiator for the next ATRP of 4-vinyl pyridine and characterized these polymers from ¹H-NMR and MALDI-TOF. Comparing with MALDI-TOF-MS, ¹H-NMR and GPC analyses, this indicates that the formation of the block copolymer can be observed. During the polymerizations, molecular weight distribution and kinetics have been evaluated from GPC traces and ¹H-NMR analyses. We further characterized the thermal properties of these block polymers by DSC and TGA. DSC measurement on the PS-b-P4VP block copolymers exhibited two glass transitions, indicating that the resulting block copolymers are phase separated. Two maxima differential peaks were observed on the TGA trace for the PS-b-P4VP block copolymers might be assigned to the decomposition of the P4VP blocks at 380 ^○C and the PS blocks at higher temperature.     

Micromechanisms of Tack of Soft Adhesives Based on Styrenic Block Copolymers

The tackiness of model soft adhesive layers based on styrene‐isoprene‐styrene block copolymers and a tackifying resin were investigated with a flat‐ended cylindrical steel probe. The contact between the probe and the adhesive was maintained for 1 s at a nominal pressure of 1 MPa before being detached at a constant velocity. The effect of resin content, probe velocity during debonding and temperature were systematically investigated. Failure was initiated by two main mechanisms: an interfacial cavitation at low debonding rates, giving relatively low adhesion energies, and a bulk cavitation process at higher debonding rates, which gave much higher adhesion energies. In both cases failure occurred at the end by interfacial detachment of fibrils. The characteristic probe velocity where the transition between these two mechanisms took place was controlled primarily by the linear viscoelastic properties of the adhesives. However, the important quantitative parameters obtained from a tack test, i.e., the maximum debonding stress and the adhesion energy, could not be predicted by the linear viscoelastic properties of these adhesives alone.     

Segmented Block Copolymers with Monodisperse Hard Segments: The Influence of H‐Bonding on Various Properties

The properties of segmented‐copolymer‐based H‐bonding and non‐H‐bonding crystallisable segments and poly(tetramethylene oxide) segments were studied. The crystallisable segments were monodisperse in length and the non‐hydrogen‐bonding segments were made of tetraamidepiperazineterephthalamide (TPTPT). The polymers were characterised by DSC, FT‐IR, SAXS and DMTA. The mechanical properties were studied by tensile, compression set and tensile set measurements. The TPTPT segmented copolymers displayed low glass transition temperatures (T_g, ?70 °C), good low‐temperature properties, moderate moduli (G′ ≈ 10–33 MPa) and high melting temperatures (185–220 °C). However, as compared to H‐bonded segments, both the modulus and the yield stress were relatively low.

     

苯乙烯类嵌段共聚物黏弹行为研究进展

综述了国内外苯乙烯类嵌段共聚物黏弹行为研究进展。着重从苯乙烯类嵌段共聚物溶液和熔体的黏弹行为两方面介绍苯乙烯类嵌段共聚物所表现出的特殊流变特性,以及流变特性与形态结构之间的关联。并基于已有的研究现状提出了苯乙烯类嵌段共聚物黏弹行为研究的前沿与重点。     

Creep and stress relaxation modeling of vinyl ester nanocomposites reinforced by nanoclay and graphite platelets

This article discusses the viscoelastic behavior of a vinyl ester (Derakane 411‐350) reinforced with 1.25 and 2.5 wt % nanoclay and exfoliated graphite nanoplatelets during short‐term creep and relaxation tests with a dynamic mechanical analyzer. Linear viscoelastic models are generally composed of one or more elements such as dashpots and springs that represent the viscous and elastic properties. Stress relaxation data from the dynamic mechanical analyzer have been used to obtain the elastic parameters based on model constitutive equations. The standard linear solid model, which is a physical model, has been used for predicting the creep deformation behavior of the vinyl ester nanocomposites over a wide temperature range. Some correlations have been made with the mechanical model, such as the effect of temperature on the deformation behavior, which is well explained by the dashpot mechanism. At lower temperatures, higher creep compliance has been observed for the vinyl ester versus the nanocomposites, whereas at temperatures near the glass‐transition temperature of the vinyl ester, creep compliance in the nanocomposites is closer in magnitude to that for the vinyl ester. The creep response of the pure vinyl ester and its nanocomposites appears to be modeled reasonably well at temperatures lower than their glass‐transition temperatures. A comparison of the predictions and experimental data from the creep tests has demonstrated that this model can represent the long‐term deformation behavior of these nanoreinforced materials reasonably well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of Block Copolymers containing Chain‐Controlled Aramid and Fluoroethylene Segments

Summary: Novel block copolymers containing aromatic polyamide (aramid) and fluoroethylene segments were synthesized by a two‐step solution polycondensation. This synthetic method could control the chain‐length of aramid segments and these copolymers could have high structural regularity. The number‐average molecular weight ( ) of one of these polymers is over 2.0 × 10⁴. Incorporating fluoroethylene segments improves the solubility of the resulting polymer compared with conventional aramids.

The synthesis of the fluoroethylene‐aramid block copolymers.     

Nanostructuration of Unsaturated Polyester by All‐Acrylic Block Copolymers, 1 ‐ Use of High‐Molecular‐Weight Block Copolymers

Nanostructuration of maleate and orthophthalic unsaturated polyester (UP) resins was achieved by the use of high molecular weight amphiphilic PBA‐b‐P(MMA‐co‐DMA)₂ triblock copolymers. PBA is fully immiscible in cured UP resins, and the miscibility of P(MMA‐co‐DMA) random copolymers can be ensured with a minimum DMA content of 12 mol‐%. When using the triblock copolymers, fully transparent and nanostructured thermosets are obtained with a minimum DMA content in the outer blocks; the value of which is higher than 12 mol‐% and depends on the UP chemical structure. Finally, the fracture toughness of nanostructured thermoset was evaluated: for a triblock copolymer content as low as 5 wt.‐%, a 50% increase of K_Ic was obtained, as compared to the neat thermoset.

     

氧化物杂质对Al2O3陶瓷力学性能与抗蠕变性的影响

采用无压烧结成型工艺,研究了氧化物杂质(碱金属、碱土金属氧化物及SiO2)对Al2O3陶瓷力学性能与抗蠕变性的影响,并利用扫描电子显微镜以及万能试验机表征样品的微观结构和力学性能;提出一种恒压试样的方法评价材料的蠕变性,测试恒压后标准试样的弯曲程度.结果表明:氧化物杂质对Al2O3陶瓷常温力学性能和高温蠕变性影响存在很大差异,常温力学性能方面,除MgO外,所研究的其它氧化物杂质均使材料抗弯强度和断裂韧性有不同程度降低,而MgO能明显提高陶瓷力学性能;另一方面,高温蠕变性受氧化物杂质影响则表现相反,MgO会导致材料抗蠕变性下降,其它氧化物杂质或多或少地提高抗蠕变性能,其中含量为1 mol％ SiO2的Al2O3陶瓷抗蠕变性能明显提高.     

SBS and SEBS block copolymers as impact modifiers for polypropylene compounds

Blends of polypropylene (PP) and thermoplastic elastomers (TPE), namely SBS (styrene‐butadiene‐styrene) and SEBS (styrene‐ethylene/1‐butene‐styrene) block copolymers, were prepared to evaluate the effectiveness of the TPE type as an impact modifier for PP and influence of the concentration of elastomer on the polymer properties. Polypropylene homopolymer (PP‐H) and ethylene–propylene random copolymer (PP‐R) were evaluated as the PP matrix. Results showed that TPEs had a nucleating effect that caused the PP crystallization temperature to increase, with SBS being more effective than SEBS. Microstructure characterization tests showed that in most cases PP/SEBS blends showed the smallest rubber droplets regardless of the matrix used. It was seen that SEBS is a more effective toughening agent for PP than SBS. At 0°C the Izod impact strength of the PP‐H/SEBS 30% b/w blend was twofold higher than the SBS strength, with the PP‐R/SEBS 30% b/w blend showing no break. A similar behavior on tensile properties and flexural modulus were observed in both PP/TPE blends. Yield stress and tensile strength decreased and elongation at break increased by expanding the dispersed elastomeric phase in the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 254–263, 2005     

Tuning the Mechanical Properties of Multiblock Copolymers Generated by Polyfunctional RAFT Agents

When employing polyfunctional reversible addition–fragmentation chain transfer (RAFT) agents (e.g., polytrithiocarbonates) in a reversible‐deactivation radical polymerization, a redistribution of the RAFT groups being connected to polymer segments occurs, which leads to a characteristic distribution of blocks in the polymer. The authors show that by adding bifunctional RAFT agents to such a system, the average number of blocks and their distribution may be tailored, proving that in principle any RAFT agent may be combined with a polyfunctional RAFT agent to tailor its topology. The authors thus add star‐shaped RAFT agents and develop multiblock copolymers of styrene and n‐butyl acrylate having incorporated star‐shaped topological features and investigate the materials via tensile testing. Using this novel mixing approach, the material toughness is substantially increased compared to multiblock copolymers obtained from pure polyfunctional RAFT agent, and stress whitening is prevented. Importantly, the approach yields copolymers with a significantly higher toughness compared to conventional blends of star and multiblock copolymers.

     

Structure and Mechanical Properties of Nanocomposites Based on an Amorphous Copolyester

Nanocomposites based on an amorphous copolyester (PCTG) were obtained by melt mixing, changing the screw speed and the nature of the surfactant, which differed in polarity and molecular volume. Using Young's modulus as a measure of the dispersion level, a less‐polar nature and a higher molecular volume of the surfactant appeared as positive structural factors for dispersion of the clay in the less‐polar PCTG. The Cloisite 20A, which led to the highest modulus (widest dispersion), was mixed at different contents with PCTG at the observed optimum screw speed (200 rpm). Intercalated structures were observed by WAXD and TEM. The dispersion was wide, as observed by TEM, and led to a large (77%) modulus increase after 7% organoclay addition and to important increases in both tensile yield stress and dimensional stability in creep.

     

Creep and Dynamic Mechanical Analysis Studies of Peroxide‐Crosslinked Ethylene‐Octene Copolymer

An ethylene‐octene copolymer (EOC) (45 wt% octene) is crosslinked using dicumyl peroxide (DCP). Differential scanning calorimetry (DSC) reveals a very low melting temperature (50 °C). The network density is evaluated by gel content. While 0.2–0.3 wt% of peroxide leads only to a molecular weight increase (samples completely dissolved in xylene), 0.4–0.6 wt% of peroxide caused network formation. High‐temperature creep was measured at 70, 120, and 200 °C at three stress levels. At 200 °C and above 0.6 wt% of peroxide, degradation due to chain scission is observed by rubber process analyzer (RPA) and is again supported by creep measurements. Residual strain at 70 °C is found to improve with increasing peroxide level. Dynamic mechanical analysis (DMA) reveals a strong influence of peroxide content on storage modulus and tan δ, in particular in the range 30–200 °C.

     

辐射接枝SBS的性能研究

采用旋转流变仪研究了苯乙烯-丁二烯-苯乙烯（sgs）嵌段聚合物接枝α-甲基丙烯酸（MAA）、甲基丙烯酸甲酯（MMA）接枝共聚物（SBS-g-MAA，SBS-g-MMA）的动态流变性能。结果表明：接枝共聚物的黏流活化能降低，温度敏感性降低；比较改性前后的共聚物的主曲线，接枝共聚物的相对分子质量分布变宽，在剪切应力作用下，黏度下降较快；接枝共聚物的相对分子质量分布变宽，接枝共聚物的抗氧化性增强。