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.

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...

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.

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.

Nanoparticle-filled ABC Star Triblock Copolymers:A Dissipative Particle Dynamics Study

The phase behavior of nanoparticle-filled ABC star triblock copolymers was investigated by dissipative particle dynamics simulation.Two typical structures,the three-color lamella and polygonal tiling structures,were selected to demonstrate the effect of filling the nanoparticle.Results showed that the filling effects were obvious on the lamellar structure but not on the tiling structure,where the high concentration of fillers can destroy the lamellar structures.The dynamic processes of nanoparticle filling were investigated for the lamellar and tiling structures,where three stages can be sorted by analyzing the system energies and chain conformations.Moreover,the mechanical properties were evaluated for the lamellar structures by exploring the interface tensions.The findings can help us understand the potential applications of microstructures based on complex block copolymers and nanoparticle mixtures.

Simulation of Surface-Induced Morphology Transition and Phase Diagram of Linear Triblock Copolymers under Spherical Confinement

In this work,the nanostructures and phase diagrams of lamella-forming and cylinder-forming ABC linear triblock copolymers confined in spherical cavities are investigated on the basis of real-space self-consistent field theory.We designate specific monomer-monomer interactions and block composition and study morphology transformation under spherical confinement with a neutral surface.Various potentially valuable morphological structures,such as two-or three-colored spheres,rotational structures,and biconcave disklike structures,are identified in the phase diagrams constructed on confining diameters.Single confinement induces an obvious transformation of self-assembled structures,which still retain some of the conformational properties of bulk structures.We then focus on phase morphology under preferential surfaces.Absorption can smooth out differences in block ratios,and similar structures can be assembled from block copolymers with different proportions.We incorporate a non-centrosymmetric feature into our spherical confinement model and design a Janus adsorption field to explore unpredictable microphase behavior.Results show that the unbalance of the block ratio causes adsorption to exert a stable shaping effect on conformation.The influence of confinement on the degree of freedom of polymer chains disrupts the influence of adsorption on the complexity and transformation activity of self-assembled structures.The theoretical results correspond to recent experimental observations and contribute to the field functional material synthesis.

Effect of poly(4-tert-butylstyrene)block length on the microphase structure of poly(ethylene oxide)-b-poly(4-vinylbenzyl chloride)-b-poly(4-tert-butylstyrene)triblock terpolymers

A series of linear poly(ethylene oxide)-b-poly(4-vinylbenzyl chloride)-b-poly(4-tert-butylstyrene)(PEO_(113)-b-PVBC_(130)-b-Pt BS_(x)or E_(113)V_(130)T_(x))triblock terpolymers with various lengths x(=20,33,66,104,215)of Pt BS block were synthesized via a two-step reversible addition-fragmentation chain transfer(RAFT)polymerization.The E_(113)V_(130)T_(x)triblock terpolymers were non-crystalline because the PVBC and Pt BS blocks strongly hindered the crystallization of PEO block.The effects of Pt BS block length x on the phase structures of E_(113)V_(130)T_(x)triblock terpolymers were investigated by combined techniques of small-angle X-ray scattering(SAXS)and transmission electron microscopy(TEM).It was found that with increasing x from20 to 215,the phase structure of E_(113)V_(130)T_(x)triblock terpolymers became more ordered and changed from disordered structure,hexagonally-packed cylinder(HEX),hexagonally perforated layer(HPL),to lamellar(LAM)phase structures.Temperature-variable SAXS measurements showed that the HEX,HPL and LAM phase structures obtained for E_(113)V_(130)T_(66),E_(113)V_(130)T_(104)and E_(113)V_(130)T_(215)by thermal annealing,respectively,were thermodynamically stable in the temperature range of 30-170℃.

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.

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。

Direct Observation of Growth and Self-assembly of Pt Nanoclusters in Water with the Aid of a Triblock Polymer Using in situ Liquid Cell Transmission Electron Microscopy （TEM）

Triblock copolymers are playing important roles in nanomaterial synthesis, and the nanomaterial forming mechanisms need to be studied in detail. In situ liquid cell transmission electron microscopy （TEM） is a powerful tool for real time observation of the dynamic growth behavior of nanomaterials in liquid with high resolution, and could be used for the above task. Here we report the observation of the growth and self-assembly of Pt nanoclusters with the aid of an ethylene oxide-propylene oxide-ethylene oxide triblock copolymer （PEO-PPO-PEO） F 127 using in situ liquid cell TEM, with the nanocluster growth and formation procedures being tracked. Nano objects were seen to appear, drift and rotate with time, and then form into certain shaped nanoclusters under the electron beam irradiation. Further interestingly, in the thicker liquid layer region, the nanoclusters appeared to be fluffy, with average size keeping increase with time, while in the thinner region, the clusters were thinner, and got densified with time. The difference in precursor availability due to liquid layer thickness and charging effects is attributed to such a phenomenon.