SYNTHESIS OF TRIBLOCK COPOLYMERS OF STYRENE AND ISOPRENE BY A NITROXIDE-MEDIATED LIVING FREE RADICAL POLYMERIZATION

The controlled free radical polymerization of styrene and isoprene initiated with benzoyl peroxide (BPO) in the presence of 2,2,6,6-tetramethyl piperidine-N-oxyl (TEMPO) at 125 'C were performed. The obtained polyisoprene and polystyrene homopolymers served as macroinitiators for block copolymerization of isoprene and styrene to synthesize poly- (styrene-b-isoprene) and poly(isoprene-b-styrene) diblock copolymers. Diblock copolymers with well-defined structures as well as controlled and narrow molecular weight distribution were obtained from the lower-mass polystyrene and polyisoprene homopolymers. These copolymers were found to be active as macroinitiators in the synthesis of the poly(styrene-b-isoprene-b-styrene) and poly(isoprene-b-styrene-b-isoprene) triblock copolymers. 1H-NMR spectroscopy and gel permeation chromatography (GPC) were used for the investigation of polymer structure, molecular weight and polydispersity (PD).

Effect of spacer length on the liquid crystalline property of azobenzene-containing ABA-type triblock copolymers via ATRP

The effect of flexible spacer length on the liquid crystalline property of ABA-type triblock copolymers containing azobenzene groups was investigated. For the study, the monomers, n-[4-(4-ethoxyphenylazo)phenoxy]alkyl methacrylates with varying methylene groups (n = 0, 2, 6) were used to synthesize a series of azobenzene-containing amphiphilic triblock copolymers PAnC–PEG–PAnC by atom transfer radical polymerization (ATRP). Differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and one-dimensional X-ray diffraction (1D WAXD) have shown that the glass transition temperatures of these copolymers decreased with increasing n, PA0C–PEG–PA0C has no mesophase, while both PA2C–PEG–PA2C and PA6C–PEG–PA6C have a nematic mesophase. These differences derive from the length of spacer groups between the polymer backbone and side-chain LC monomers.

SYNTHESIS AND CHARACTERIZATION OF POLY(AMINO ACID-UREA)S COMPRISING NOVEL TRIBLOCK COPOLYMERS OF POLY(TETRAHYDROFURAN)AND POLY(γ-BENZYL L-GLUTAMATE)S

A kind of novel triblock copolymers of poly(γ-benzyl L-glutamate)-b-poly(tetrahydrofuran)-b-poly(γ-benzyl L-glutamate)s(PBLG-b-PTHF-b-PBLG)was synthesized by using bis(3-aminopropyl)terminated polytetrahydrofuran to initiate the ring-opening polymerization ofγ-benzyl L-glutamate N-carboxyanhydride(BLG-NCA).The corresponding multiblock poly(amino acid-urea)s were prepared in one-pot protocol from the chain extension of PBLG-b-PTHF-b-PBLG with MDI.The resulting triblock and multiblock copolymers were characterized by FTIR,~1H-NMR,^(13)C-NMR and GPC techniques.It is demonstrated that the chain extension has taken place to give rise to the copolymers with the well-defined block composition and narrow molecular weight distribution.A distinct T_g arising from the hard-segments was observed in all the copolymers.Their mechanical properties showed an increasing trend with the molecular weight enhancement of the prepolymers.

SELF ASSEMBLY OF ABC TRIBLOCK COPOLYMER THIN FILMS ON A BRUSH-COATED SUBSTRATE

Self assemblies of ABC triblock copolymer thin films on a densely brush-coated substrate were investigated by using the self-consistent field theory.The middle block B and the coated polymer form one phase and the alternating phase A and phase C occur when the film is very thin either for the neutral or selective hard surface(which is opposite to the brushcoated substrate).The lamellar phase is stable on the hard surface when it is neutral and interestingly,the short block tends to stay on this hard surface...

Monte Carlo Simulation for the Adsorption of Symmetric Triblock Copolymers

The adsorption behavior of symmetric triblock copolymers, Am/2BnAm/2, from a nonselective solvent at solid-liquid interface has been studied by Monte Carlo simulations on a simple lattice model. Either segment A or segment B is attractive, while the other is non-attractive to the surface. Influences of the adsorption energy, bulk concentration, chain composition and chain length on the microstructure of adsorbed layers are presented. The results show that the total surface coverage and the adsorption amount increases monotonically as the bulk concentration increases. The larger the adsorption energy and the higher the fraction of adsorbing segments, the higher the total surface coverage is exhibited. The product of surface coverage and the proportion of non-attractive segments are nearly independent of the chain length, and the logarithm of the adsorption amount is a linear function of the reciprocal of the reduced temperature. When the adsorption energy is larger, the adsorption amount exhibits a maximum as the fraction of adsorbing segment increases. The adsorption isotherms of copolymers with different length of non-attractive segments can be mapped onto a single curve under given adsorption energy. The adsorption layer thickness decreases as the adsorption energy and the fraction of adsorbing segments increases, but it increases as the length of non-attractive segments increases. The tails mainly govern the adsorption layer thickness.

Morphologies of Core-Shell-Cylinder-Forming ABC Star Triblock Copolymers in Nanopores

The self-assembly behavior of ABC star triblock copolymers can lead to a large number of nanostructures. Indeed, many new and interesting structures have already been discovered and proven to be hotspot in soft matter physics research. In this work, we introduce different phase diagrams of core-shell-cylinder-forming ABC star triblock copolymers under different conditions, including in-bulk and pore geometries with different sizes. The relation between the pore size geometries and their corresponding structures are also revealed. The different properties of the surface potential field that significantly affect the self-assembly process of ABC star triblock copolymers are investigated as well.

Effect of Poly(ε-caprolactone-b-tetrahydrofuran)Triblock Copolymer Concentration on Morphological,Thermal and Mechanical Properties of Immiscible PLA/PCL Blends

In this study a low molecular weight triblock copolymer derived fromε-caprolactone and tetrahydrofuran was used as a non-reactive compatibilizer of immiscible PLA/PCL blends.Ternary blends with 0,1.5 wt%,3 wt%and 5 wt% copolymer and about 75 wt%PLA were prepared by single screw extrusion and characterized by scanning electron microscopy(SEM),differential scanning calorimetry(DSC),dynamic mechanical analysis(DMA),tensile and Izod impact testing.SEM micrographs showed that the size of the dispersed PCL domains was practically constant regardless of copolymer concentration.This result can be explained by the low shear rate employed during processing step and a decrease of PCL viscosity by presence of the triblock copolymer.However,when the copolymer concentration increased,strain at break of PLA/PCL blends also increased.PLA/PCL blend with 0 wt% copolymer presented 2%strain at break,whereas PLA/PCL blend with 5 wt%copolymer exhibited 90%.

STUDIES ON MICELLE BEHAVIORS OF STYRENE-BUTADIENE-STYRENE (SBS) TRIBLOCK COPOLYMERS IN METHYL ETHYL KETONE (MEK) BY POSITRON ANNIHILATION TECHNIQUE

Positron annihilation technique was used to study the micelle behaviors of two SBS triblock copolymers in MEK solvent at different temperatures. Annihilation lifetime τ_3 of ortho-positronium (o-Ps) exhibited an obvious transition from shorter lifetime to longer lifetime with temperature. It was attributed to the change of micelle behavior of SBS copolymer molecules in the solution. Experimental results of sedimentation velocity of ultracentrifuge were also reported.

Electrorheological Properties of Suspensions of PAn-PEO-PAn Triblock Copolymer Particles

The PAn-PEO-PAn triblock copolymer with the PEG chain length of 400 was synthesized by chemical oxidation copolymerization of aniline and α,ω-bis（p-aminophenyl）poly（ethylene glycol）and characterized by FT-IR and TEM.The experimental results show that the copolymer particles are of μtypical core-shell structure after the self-assembly process in water.Its conductivity is much lower than that of the pure PAn.The suspension containing 20 vol% PAn-PEO-PAn tiblock copolymer in silicone oil exhibits.a typical electrorheological （ER） effect in DC electric field.while it shows a lower leakage current density than that of the pure PAn-based ER fluids.Therefore,the PEO shell hinders the electric hop among PANI chains and decreases the current density of ER fluids in an external electric field.at the same time the interface polarity improves the ER effects.

An Overview of the Synthesis and Gene Transfer Properties of Triblock Copolymers Poly(2-Methyl-2-Oxazoline-b-Tetrahydrofurane-b-2-Methyl-2-Oxazoline)

The synthesis of poly(2-methyl-2-oxazoline-b-tetrahydrofurane-b-2-methyl-2-oxazoline) triblock copolymer of low molar mass has been carried out. Characterization of the purified polymer by 1H and 13C NMR spectroscopies is described. These block copolymers did not give DNA containing polyplexes. The in vivo transfection properties were investigated by injection of tibialis muscles and intratracheal administration of female Swiss mice. These triblock copolymers with a molar ratio [2-methyl-2-oxazoline units]/[tetrahydrofurane units] in the 3 - 5 range gave a higher transfection efficiency than that of Lutrol or of PE6400 which are the gold standards of this transfection technique. Hydrolysis increased the performances of muscle transfection, showing the beneficial effect of the presence of positive charges, but was clearly detrimental to the transfection efficiency of pulmonary epithelium.

Phase Behavior of Sphere-Forming Triblock Copolymers in Films

The self-assembly of sphere-forming triblock copolymers confined between two thin homogeneous surfaces is investigated based on mean-field dynamic density functional theory. The morphologies deviating from the bulk sphere-forming phase are revealed, including cylinders oriented perpendicular to the surface, cylinders oriented parallel to the surface, perforated lamellae and lamellae by varying film thickness and surface field strength. The phase diagram of surface reconstruction is also constructed. By comparing the present phase diagram with the other relevant phase diagram for the cylinder-forming triblock copolymer film, the difference between the sphere-forming and the cylinder-forming triblock copolymer thin film is discussed.

Thermal Stability Improvement and Structural Change of Oil Gels Formed by Styrene-Butadiene-Styrene Triblock Copolymer Induced by Adding Poly(phenylene ether)

The thermal stability of oil gels formed by styrene-butadiene-styrene triblock copolymer (SBS) was improved by adding a small amount of poly(phenylene ether) (PPE), which has a higher glass transition temperature (Tg). In naphthenic oil which is a good solvent for the butadiene blocks, but a non-solvent for the styrene blocks and PPE, PPE was selectively included into styrene blocks in SBS, and induced the increase of the Tg of these blocks. The melting temperature determined by viscoelastic measurements and softening temperature of the gels were elevated by adding PPE, while no significant change was detected by adding polystyrene. The gel became opaque by adding PPE, and partially separated phases were observed by field emission scanning electron microscopy (FE-SEM). The dependence of the viscoelastic behavior on the PPE concentration can be explained by the structural change observed by FE-SEM.

MONTE CARLO SIMULATION OF TRIBLOCK COPOLYMER/HOMOPOLYMER BLEND FILMS

The morphologies of triblock copolymer/homopolymer blend films, ABA/A and ABAIB, confined between two neutral hard walls were studied via Monte Carlo （MC） simulation on a simple .cubic lattice. The effects of φh （the volume fraction of homopolymer） and Md/Mb （the molecular weight of homopolymer in relation to that of the corresponding blocks in the copolymer） on the morphologies were investigated in detail.

Self-assembly of block copolymers grafted onto a flat substrate:Recent progress in theory and simulations

Block copolymers are a class of soft matter that self-assemble to form ordered morphologies on the scale of nanome- ters, making them ideal materials for various applications. These applications directly depend on the shape and size of the self-assembled morphologies, and hence, a high degree of control over the self-assembly is desired. Grafting block copolymer chains onto a substrate to form copolymer brushes is a versatile method to fabricate functional surfaces. Such surfaces demonstrate a response to their environment, i.e., they change their surface topography in response to different external conditions. Furthermore, such surfaces may possess nanoscale patterns, which are important for some applica- tions; however, such patterns may not form with spun-cast films under the same condition. In this review, we summarize the recent progress of the self-assembly of block copolymers grafted onto a flat substrate. We mainly concentrate on the self-assembled morphologies of end-grafted AB dibloek eopolymers, junction p0int-grafted AB diblock copolymers （i.e., Y-shaped brushes）, and end-grafted ABA triblock copolymers. Special emphasis is placed on theoretical and simulation progress.

Solvent-Induced Phase-Inversion and Electrical Actuation of Dielectric Copolymer Films

Block copolymers posses inherently the ability of form a variety of phase-separated microdomain structures. The lengths of block segments and the selectivity of the solvent are primary factors affecting the resultant morphology. This paper investigated the effect of casting solvents on the morphologies and electrical actuation of poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate) (PMMA-PnBA-PMMA) triblock copolymer films comprising PMMA hard segment and PnBA soft segment. Transmission electron microscopy and confocal laser scanning microscopy observation revealed that PMMA and PnBA segments were assembled into various micro- and nano-sized phase structures where either of them formed continuous phase. This implies that continous phase could be inversed by used casting solvents. Solvent-dependent phase morphologies had a significant effect on the electrical actuation results. Increase of the PnBA contents and the continuous phases of PnBA soft segments improved both of electrical actuation and dielectric constant, indicating that solvent-induced phase separation modulates the electrical actuation of dielectric films. The significance of the role of solvent selectivity and the major continuous phase of the polymer in defining the morphology and electrical actuation of the self-assembled block copolymer structure are discussed.

三嵌段共聚物临界胶束浓度与分子横截面积测定

采用双毛细管最大泡压法装置测定了25℃条件下不同浓度非离子表面活性剂聚乙二醇-聚丙二醇-聚乙二醇三嵌段共聚物(PEG-PPG-PEG;Pluronic L-64)对溶液表面张力的影响。采用Origin软件对数据进行处理分析,计算得到其临界胶束浓度(CMC)。基于吉布斯(Gibbs)与朗格缪尔(Langmuir)吸附等温式,对溶液表面张力与浓度关系进行一步非线性拟合,计算获得吸附分子的横截面积。该实验扩展了最大泡压法测定表面张力的应用,提高了学生分析处理实验数据的能力。

Enhanced stability of nitrogen-doped carbon-supported palladium catalyst for oxidative carbonylation of phenol

Enhancing the stability of supported noble metal catalysts emerges is a major challenge in both science and industry.Herein,a heterogeneous Pd catalyst(Pd/NCF)was prepared by supporting Pd ultrafine metal nanoparticles(NPs)on nitrogen-doped carbon;synthesized by using F127 as a stabilizer,as well as chitosan as a carbon and nitrogen source.The Pd/NCF catalyst was efficient and recyclable for oxidative carbonylation of phenol to diphenyl carbonate,exhibiting higher stability than Pd/NC prepared without F127 addition.The hydrogen bond between chitosan(CTS)and F127 was enhanced by F127,which anchored the N in the free amino group,increasing the N content of the carbon material and ensuring that the support could provide sufficient N sites for the deposition of Pd NPs.This process helped to improve metal dispersion.The increased metal-support interaction,which limits the leaching and coarsening of Pd NPs,improves the stability of the Pd/NCF catalyst.Furthermore,density functional theory calculations indicated that pyridine N stabilized the Pd^(2+)species,significantly inhibiting the loss of Pd^(2+)in Pd/NCF during the reaction process.This work provides a promising avenue towards enhancing the stability of nitrogen-doped carbon-supported metal catalysts.

活性三嵌段共聚物的凝胶化转变

活性物质的自推进特征引发了许多非平衡自组织现象,而聚合物链的构象自由度可以使链产生独特的平衡自组装行为,这激发了活性物质与聚合物物理的交叉研究.本文通过分子动力学模拟,研究了自驱动活性对ABA型三嵌段共聚物凝胶化转变的调控.研究结果表明活性嵌段共聚物凝胶的塌缩源于自驱动活性引起的网络链运动,活性越大则凝胶网络越容易产生大直径空洞.在凝胶网络的拓扑缺陷方面,当A嵌段之间吸引强度较大时,环链比例随活性力增强而增大,吸引强度较小时情况则相反.交联点的分支数随活性的变化除了受到吸引强度的影响,还与链刚性有关.在动力学方面,活性聚合物的定向运动会引发稳定聚合物凝胶整体的反常扩散.本文的研究有助于增进对活性聚合物集体行为的认识,为高分子活性材料的设计和应用提供了新的思路.

层状ABC星型三嵌段共聚物和纳米颗粒的自组装

采用耗散粒子动力学模拟方法研究了层状ABC星型三嵌段共聚物和纳米颗粒的协同自组装.主要考虑了不同密度下纳米颗粒的聚集行为及其对层状结构的影响.当纳米颗粒密度较低时,纳米颗粒呈囊泡状聚集;当纳米颗粒密度较高时,纳米颗粒呈柱状聚集.通过分析体系能量和共聚物链的回转半径研究了该动力学过程;通过界面张力的计算,对体系中微结构的力学性能进行了探索.这些发现不仅有助于人们了解复杂的嵌段共聚物,也可以为探索嵌段共聚物和纳米颗粒的微结构提供思路,对研究嵌段共聚物纳米复合材料的潜在应用提供帮助.