Investigation of the micromechanical deformation behavior of styrene–butadiene star block copolymer/polystyrene blends with high‐voltage electron microscopy

The deformation behavior of blends consisting of a styrene–butadiene star block copolymer and a polystyrene homopolymer was studied by high‐voltage electron microscopy with a tensile device. The mechanical properties and micromechanical deformation mechanisms in the star block copolymer/polystyrene blends were directly influenced by their morphology. Although the pure block copolymer deformed in a very unequal manner (because of a thin‐layer‐yielding mechanism) and revealed no local deformation zones, a transition to the formation of crazelike zones was observed in the blends. This transition in the deformation mechanisms was correlated to the abrupt change in the macroscopic strain at break of the injection‐molded specimens. At lower contents of added polystyrene, a craze‐stopping mechanism was observed, whereas the blends with higher polystyrene contents demonstrated crazing like that in pure polystyrene. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1157–1167, 2003     

Morphology and micromechanical behaviour of styrene/butadiene block copolymers and their blends with polystyrene

The correlation between the morphology and the deformation mechanism in styrene/butadiene block copolymers having modified architecture and in blends with homopolymer polystyrene (hPS) was studied. It was demonstrated that the morphology formation in the block copolymers is highly coupled with their molecular architecture. In particular, the micromechanical behaviour of a star block copolymer and its blends with polystyrene was investigated by using electron microscopy and tensile testing. A homogeneous plastic flow of polystyrene lamellae (thin layer yielding) was observed if the lamella thickness was in the range of 20 nm. The deformation micromechanism switched to the formation of craze-like deformation zones when the average PS lamella thickness changed to about 30 nm and more.     

Morphology and deformation behaviour of SBS/PS blends: a combined microscopic and spectroscopic study

Correlation between morphology and micromechanical deformation behaviour of blends consisting of a lamellae-forming linear styrene/butadiene block copolymer and polystyrene homopolymer (hPS) was studied by different microscopic techniques (transmission electron microscopy and scanning electron microscopy) and rheo-optical Fourier transformed infrared spectroscopy. Attributable to a change in morphology from well-ordered lamellae to a distorted one, a transition in deformation mechanism from homogeneous plastic flow of the lamellae to formation of local craze-like deformation zones was observed on addition of hPS. The latter led to a drastic reduction in elongation at break. An abrupt depression in the degree of orientation of the polystyrene (PS) and the polybutadiene (PB) phases in the blends suggested that the failure occurs at the interface between the added hPS and PS blocks of the block copolymer.     

Double Yielding in a Styrene/Butadiene Star Block Copolymer

Summary: The morphology and tensile deformation behaviour of a highly asymmetric styrene/butadiene star block copolymer (polystyrene (PS) content = 74%) containing random PS‐co‐PB (polybutadiene) copolymer as a rubbery phase were investigated. The existence of double yielding, similar to that observed in some semicrystalline polymers, was detected in this nanostructured amorphous polymer. The observed phenomenon may be correlated with two different micromechanical processes taking place at the initial stage of deformation.

The stress‐strain curve of the star block copolymer prepared here (each curve represents a different method). The two yield points are clearly visible (labelled I and II).     

Crew‐cut aggregates from self‐assembly of blends of polystyrene‐b‐poly(acrylic acid) block copolymers and homopolystyrene in solution

The formation and morphological characteristics of crew‐cut aggregates from blends of polystyrene‐b‐poly(acrylic acid) diblock copolymer and polystyrene homopolymer in solution were studied by static light scattering, transmission electron microscopy and size exclusion chromatography. The crew‐cut aggregates, consisting of a polystyrene core and a poly(acrylic acid) corona, were prepared by direct dissolution of the polymer blends in a selective solvent mixture consisting of 93 wt % dimethylformamide and 7 wt % water. It is found that the aggregation behavior depends strongly on the relative volume fractions of the block copolymer and homopolymer in the blends. This is a result of the difference in solubility between the copolymer and the homopolymer in solution which, in turn, influences their miscibility and mutual solubility and consequently the morphology of the formed crew‐cut aggregates. Specifically, when the homopolymer fraction is low, it is mainly dissolved in the cores of the crew‐cut aggregates formed by the block copolymer. When the homopolymer fraction exceeds its solubility limit in the copolymer micelles, aggregates of another type are formed which contain a major fraction of the homopolymer. These aggregates are usually much larger than the primary micelles and have an internal structure due to the formation of reverse micelles from the dissolved block copolymer chains. The importance of thermodynamic vs. kinetic aspects during the formation of the crew‐cut aggregates is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1469–1484, 1999     

Extrusion Induced Morphologies and Properties of Layered Block Copolymer/Polystyrene Mixtures

Using transmission electron microscopy (TEM) and tensile testing, we investigated the morphology and the micro-deformation processes in a new kind of highly asymmetric polystyrene/polybutadiene based triblock copolymer and its blends with general purpose polystyrene (GPPS). The emphasis has been put on the analysis of blends morphology evolved under extrusion conditions and the impact of the later on the micromechanical behaviour of the blends. It was found that the phase separated structures were strongly oriented along the extrusion direction leading to the anisotropic mechanical behaviour. The blends showed more ductile performance and lesser strength on loading the sample perpendicular to the extrusion direction. The ductile to brittle transition was observed when the morphology of the blends was dominated by the glassy phase for 60 wt.-% GPPS.     

Influence of Domain Size on Toughness of Poly(styrene‐block‐butadiene) Star Block Copolymer/Polystyrene Blends

Summary: The toughness of poly(styrene‐block‐butadiene) star block copolymer/polystyrene (PS) blends have been investigated using the essential‐work‐of‐fracture approach. The blends show a co‐continuous or layer‐like structure of polystyrene‐rich and polybutadiene‐rich domains arising from the used extrusion process. A tough‐to‐brittle transition at a critical domain size of polystyrene‐rich domains of about 50 nm and a maximum in the non‐essential work of fracture at 20–30% PS (co‐continuous morphology) have been found.

Non‐essential work of fracture as a function of the mean thickness of polystyrene‐rich domains, demonstrating a tough‐to‐brittle transition at a critical domain thickness about 50 nm. AFM micrograph of a star block copolymer/PS‐blend containing 40% PS.     

Toughness Enhancement of Nanostructured Amorphous and Semicrystalline Polymers

An overview is given of different micromechanical deformation processes leading to an enhancement of toughness in heterophase polymers. The well-known mechanism of rubber or particle toughening of semicrystalline polymers was studied in HDPE and PP blends. In particular, the micromechanical processes in the semicrystalline polymer strands between modifier particles were investigated in detail, revealing processes of separation, yielding, breaking and twisting of lamellae. These processes are compared with lamellae forming amorphous SBS block copolymers with alternating soft (polybutadiene) and hard (polystyrene) layers. Depending on the deformation direction, the mechanism of thin layer yielding or chevron formation appears. In both polymeric systems, the initial stage of deformation is characterized by a plastic yielding of the soft phase with a reorganization of the hard (glassy or crystalline) lamellae. The second stage is determined by the alignment of the hard phase towards the deformation direction and the plastic yielding. Detailed comparison of these similar mechanisms in very different polymers with similar nanostructured morphology should help to improve toughening of amorphous as well as semicrystalline polymers.     

PTHF-b-PMMA/PVC共混体系的相容性和结晶行为

研究了具有焓效应的聚四氢呋喃-聚甲基丙烯酸甲酯两嵌段共聚物与聚氯乙烯PTHF-b-PMMA/PVC)共混体系的相容性和结晶行为. 结果表明, 其相容性比AB/A型嵌段共聚物共混体系的相容性要好得多; 与PTHF部分相容的PVC对PTHF微区的结晶行为可产生很大的影响. 应用有关理论和模型很好地解释了结晶行为的这种变化.     

聚苯乙烯溶胀聚苯乙烯－聚丁二烯－聚苯乙烯三嵌段共聚物微区的研究

嵌段共聚物/均聚物共混体系,各嵌段会形成各自的相,并且嵌段间的连接点一定在两相之间的界面上,这一要求极大地影响了嵌段共聚物/均聚物共混体系的链构象和相行为.     

用新型茂钛催化剂制备的苯乙烯/丁二烯嵌段共聚物的结构表征

用CpTi(OBz)3/MAO催化体系合成的苯乙烯／丁二烯嵌段共聚合产物经丁酮、甲苯、四氢呋喃、氯仿连续抽提,并用已烷对丁酮的可溶级分进行再抽提;不同级分分别用GPC、^13C -NMR、DSC和WAXD等手段进行分析和表征。发现嵌段共聚物主要存在于氯仿可溶级分中,丁酮可溶级分基本上是无规聚苯乙烯和聚丁二烯组成的混合物（己烷可溶级分为聚丁二烯,不溶级分为无规模聚乙烯）。GPS谱图表明该嵌段共聚反应具有单催化活性中心的聚合特征,^13C-NMR谱图显示该嵌段共聚物分子链由间规聚苯乙链段和聚丁二烯链段组成,WAXD图谱显示嵌段共聚物有较高的结晶度。     

Modification of the morphology of P(S-b-EO) templated thin TiO2 films by swelling with PS homopolymer

For the controlled modification of sol-gel-templated polymer nanocomposites, which are transferred to a nanostructured, crystalline TiO2 phase by a calcination process, the addition of a single homopolymer was investigated. For the preparation, the homopolymer polystyrene (PS) is added in different amounts to the diblock copolymer P(S-b-EO) acting as a templating agent. The homopolymer/diblock copolymer blend system is combined with sol-gel chemistry to provide and attach the TiO2 nanoparticles to the diblock copolymer. So-called good-poor solvent-pair-induced phase separation leads to the formation of nanostructures by film preparation via spin coating. The fabricated morphologies are studied as a function of added homopolymer before and after calcination with atomic force microscopy, field emission scanning electron microscopy, and grazing incidence small-angle X-ray scattering. The observed behavior is discussed in the framework of controlling the block copolymer morphologies by the addition of homopolymers. At small homopolymer concentrations, the increase in homopolymer concentration changes the structure size, whereas at high homopolymer concentrations, a change in morphology is triggered. Thus, the behavior of a pure polymer system is transferred to a more complex hybrid system.     

Morphological and Structural Studies of sPS/aPS Blends

Inrecentyears,thenewsedricrystallinepolymersyndiotacticp0lystyrene(sPS)hasat-ITactedmuchattentionduetoitsg0odchendcalresistanceandenhancedmechanicalperformanceatelevatedtemPeratUre.'H0wever,itexhibitshighbrittlenessandpoorimPact-resistanceandtCar-resistance.2Therefore,itisnecessarytomodifyitwithtougheningpolyIners.AsimPlemeth0dto0verc0methedriscibilityofatwo-phaseblendofsPSandatougheningpolymristotwrovetheinterfacialaffmity,wheretheadditionofablockcoP0lymerisconsideredtobemosteffective.3…     

最有效的相容剂是两嵌段还是多嵌段聚合物?

Monte Carlo simulations were used to investigate the compatibilizing behaviors of multi-block copolymers with different architectures in A/B/(block copolymer) ternary blends. The volume fraction of homopolymer A, employed as the dispersed phase, was 19%. The simulations illustrate how a di- or multi-block copolymer aggregates at the interfaces and influences the phase behaviour of such incompatible polymer blends. The di-block copolymer chains tend to "stand" on the interface whereas the multi-block chains lie on the interface.In comparison with the dj-block copolymer, the block copolymers with 4, or 10 blocks can occupy more areas on the interface, and thus the multi-block copolymers have higher efficiency for the retardation of the phase separation.     

Helical phase from blending of chiral block copolymer and homopolymer

The phase behavior of the binary blends of polystyrene-b-poly(L-lactide) chiral block copolymer (BCP*) and polystyrene homopolymer (HS) is found to be strongly dependent on the molecular weight (M(n)) of the HS. A helical phase is formed in the blends with low-M(n) HS due to an enhancement of helical steric hindrance.     

Microindentation Hardness of Nanostructured Thermoplastic Materials

Summary: The micromechanical behaviour of various thermoplastics based nanocomposites was investigated with the aid of the microindentation technique. The materials studied were microphase separated styrene-butadiene block copolymer systems and several thermoplastics reinforced with nano-sized fillers having variable dimensionality. It was found that the microhardness behaviour of the nanocomposites studied was strongly influenced by the dimensionalities of the filler. Due to large surface to volume-ratio one- and two-dimensional fillers exhibit a far better reinforcing behaviour than the three dimensional ones. In case of nanostructured block copolymers, the microhardness is not determined by the total polystyrene (PS)/polybutadiene (PB) composition alone but diminishes gradually in presence of freely standing dangling polybutadiene chains even if the morphology of the systems remains unaltered.     

Compatibilizing effect of polyarylate-polystyrene block copolymer in polyarylate/polystyrene blends

The compatibilizing effect of polyarylate-polystyrene (PAR-PS) block copolymer prepared from macroazo initiator was examined in polyarylate/polystyrene blends from the view-points of morphology, density, and thermal, mechanical, and rheological properties. PARPS block copolymer enhanced the mutual dissolution of the homopolymers. Reduced dispersed-domain size and increased density showed the efficiency of the block copolymer as a compatibilizing agent. Results from mechanical and rheological properties could also be explained by the compatibilizing effect of PAR-PS block copolymer in the blends. © 1994 John Wiley & Sons, Inc.     

Roll-Casting of block copolymers and of block copolymer-homopolymer blends

An improved technique for casting highly oriented films of block copolymers from solutions subjected to flow is presented. Polymer solutions were rolled between two counter-rotating adjacent cylinders while at the same time the solvent was allowed to evaporate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. Using this method known as ‘roll-casting’ we present in this paper a study of the morphology of polystyrene-polybutadiene-polystyrene (PS/PB/PS) triblock copolymer cast with and without additional high molecular weight homopolymers. The pure copolymer films consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix in a near single-crystal structure. Blends of copolymer with high molecular weight polystyrene and/or polybutadiene, phase separated into ellipsoidal regions of homopolymer embedded in an oriented block copolymer matrix. Annealing the films resulted in conversion of the homopolymer regions to spheres accompanied by some misalignment of the copolymer microdomains. The morphology of these films as revealed by TEM is discussed. A brief discussion of the flow field that develops in the experimental system is also presented and its similarity to the flow field of our previous work is shown. © 1994 John Wiley & Sons, Inc.     

Influence of Reactive Compatibilization on the Morphology of Polypropylene/Polystyrene Blends

To study the efficiency of different mechanisms for reactive compatibilization of polypropylene/polystyrene blends (PP/PS blends), main chain or terminal-functionalized PP and terminal-functionalized PS have been synthesized by different methods. While the in-situ block and graft copolymer formation results in finer phase morphologies compared to the corresponding non-reactive blends, the morphology development in the ternary blend system PP/PS + HBP (hyperbranched polymer) is a very complex process. HBP with carboxylic acid end groups reacts preferably with the reactive sites of the oxazoline functionalized PS (PS-Ox) and locates mainly within the dispersed PS-Ox phase. A bimodal size distribution of the PS-Ox particles within the oxazoline modified PP (PP-Ox) matrix phase is observed with big PS-Ox particles (containing the HBP as dispersed phase) and small PS-Ox particles similar in size to the unimodal distributed particles in the non-reactive PP-Ox/PS-Ox blends. Factors influencing the morphology are discussed.     

Compatabilization of polystyrene/polypropylene blends by styrene–butadiene block copolymers with differing polystyrene block lengths

Compatibilization of polystyrene/polypropylene (PS/PP) blends, by use of a series of butadiene–styrene block copolymers was studied by means of small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). The compatibilizers used differ in molar mass and the number of blocks. It was shown that the ability of a block copolymer (BC) to participate in the formation of an interfacial layer (and hence in compatibilization) is closely associated with the molar mass of styrene blocks. If the styrene blocks are long enough to form entanglements with the styrene homopolymer in the melt, then the BC is trapped inside this phase of the PS/PP blends, and its migration to the PS/PP interface is difficult. In this case, the BC does not participate in the formation of the interfacial layer nor, consequently, in the compatibilization process. On the other hand, the BC's with the molar mass of the PS blocks below the critical value are proved to be localized at the PS/PP interface. This preferable entrapping of some styrene–butadiene BC's in the PS phase of the PS/PP blend is, of course, connected to the differing miscibility of the BC blocks with corresponding components of this blend. Although the styrene block is chemically identical to the styrene homopolymer in the blend, the butadiene block is similar to the PP phase. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1647–1656, 1999