Relating microhardness to morphology in styrene/butadiene block copolymer/polystyrene blends

The microhardness behaviour of binary blends comprising a styrene/butadiene star block copolymer and polystyrene homopolymer (hPS) over a wide composition range is investigated. In particular, the interrelation between the morphology, tensile properties (such as yield stress σ_Y and the Young's modulus, E) and the microhardness H is explored. As in the case of microphase separated block copolymers and binary block copolymer blends, as reported in preceding publications, a clear deviation in the microhardness behaviour from the additivity law is observed. The lamellar block copolymer system is compared with the nanostructure of semicrystalline polymers having a lamellar morphology. A dependence of H upon PS lamellar thickness is found. For the samples with lamellar morphology the hardness value was found to correlate with the mechanical parameters obtained by uni-axial tensile testing according to: H/σ_Y∼2.2 and E/H∼22.     

Morphology and micromechanical deformation behavior of styrene–butadiene block copolymers. III. Binary blends of asymmetric star block copolymer with general‐purpose polystyrene

The correlation between morphology, mechanical properties, and micromechanical deformation behavior of the blends consisting of an asymmetric styrene/butadiene star block copolymer (ST2‐S74, total styrene volume content Φ_PS = 0.74) and general‐purpose polystyrene (GPPS) was investigated using transmission electron microscopy and uniaxial tensile testing. Addition of 20 wt % of GPPS to the block copolymer resulted in a drastic reduction in strain at break, indicating the existence of critical PS lamella thickness D_c. Above D_c lamellar block copolymers displayed a transition from ductile to brittle behavior, substantiating the mechanism of thin layer yielding proposed for lamellar star block copolymers. The blends showed a variety of deformation structures ranging from classical crazelike zones to those with internal shearlike components. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1208–1218, 2004     

Morphology and micromechanical behavior of binary blends comprising block copolymers having different architectures

Morphology and deformation behavior of binary blends comprising styrene/butadiene block copolymers (polystyrene content, Φ_PS∼0.70) having different molecular architectures were studied by means of transmission electron microscopy and tensile testing. In contrast to the binary diblock copolymer blends discussed in literature, the phase separation behavior of the blends investigated was found to be strongly affected by asymmetric molecular architecture. The blends showed macrophase separated grains, in which the structures resembled the microphase morphology of none of the blend components. Unlike the classical rubber-modified or particle-filled thermoplastics, neither debonding at the particle/matrix interface nor the particle cavitation was observed in these nanostructured blends. The microdeformation of the blends revealed plastic drawing of polystyrene lamellae or PS struts dispersed in rubbery matrix and orientation of the whole deformation structures along the strain direction.     

Influence of the extrusion process on the morphology and micromechanical behavior of polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene star block copolymer/homopolystyrene blends

The influence of the extrusion process on the morphology and micromechanical behavior of an asymmetric polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene (SBS) star block copolymer and its blends with general‐purpose homopolystyrene (hPS) was studied with films prepared with a single‐screw extruder. The techniques used were transmission electron microscopy and uniaxial tensile testing. Unlike the pure SBS block copolymer possessing a gyroid‐like morphology, whose deformation was found to be insensitive to the processing conditions, the mechanical properties of the blends strongly depended on the extrusion temperature as well as the apparent shear rate. The deformation micromechanism was primarily dictated by the blend morphology. The yielding and cavitation of the nanostructures were the principal deformation mechanism for the blends having a droplet‐like microphase‐separated morphology, whereas cavitation dominated for the blends containing macrophase‐separated layers of polystyrene. The mechanical properties of the blends were further examined with respect to the influence of the temperature and shear rate on the phase behavior of the blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Deformation and alignment of lamellae in melt extension of blends of a styrene‐butadiene block copolymer with polystyrene

The development of the morphology and the alignment of lamellae in melt elongation of blends of an asymmetric linear styrene‐butadiene block copolymer (LN3) and polystyrene (PS 158K) was investigated. PS 158K and LN3 formed two‐phase polymer blends with PS 158K resp. LN3 inclusions, depending on the concentration of polystyrene. The block copolymer was arranged in a lamellar phase with a lamellae thickness of ～ 13 nm. Our rheological experiments revealed that the complex modulus, the elongational viscosity and the recovered stretch of the blends primarily resulted from a superposition of the properties of the blend components. In melt elongation, pure LN3 started to crumple at a small Hencky strain. In the blends, the presence of the PS 158K inclusions led to a macroscopically more uniform elongation, but with an anisotropic Poisson ratio. The LN3 inclusions in the PS 158K matrix were deformed into a filament‐like shape. In the blends with a LN3 matrix the alignment of the block copolymer lamellae parallel to the loading direction increased with applied extensional strain. In the latter case, the lamellae thickness did not decrease significantly. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology and micromechanical deformation behavior of styrene–butadiene block copolymers. IV. Structure–property correlation in binary block copolymer blends

The structure–property correlation in blends consisting of styrene/butadiene block copolymers forming alternating polystyrene (PS) and polybutadiene (PB) lamellae, and PS domains in rubbery matrix was investigated by different microscopic techniques (transmission electron microscopy, scanning force microscopy, and scanning electron microscopy), uniaxial tensile testing, and dynamic mechanical analysis. Unlike the pure lamellar block copolymer, the blends showed predominantly disordered wormlike morphology formed by the intermolecular mixing. These structures allowed a precise control of stiffness/toughness ratio of the blends over a wide range. The blends showed a gradual transition from predominantly viscoplastic to elastomeric behavior with increasing triblock copolymer content. The results demonstrated that the binary block copolymer blends provide the unique possibility of tailoring mechanical properties on the basis of nanostructured polymeric materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1219–1230, 2004     

Ternary blends of high‐density polyethylene–polystyrene–poly(ethylene/butylene‐b‐styrene) copolymers: Properties and orientation behavior in plane–strain compression

Ternary blends of high‐density polyethylene (HDPE) with atactic polystyrene (PS) and styrene–ethylene/butylene–styrene block copolymer (SEBS) were deformed by plane–strain compression in a channel die. The samples were deformed up to the true strain of 1.8 (compression ratio of 6) at 100°C. Thermal and mechanical properties of the deformed blends were studied in addition to the study of the deformation process. The basic mechanism of plastic deformation is crystallographic slip, the same as that active in deformation of plain HDPE and binary blends of HDPE and PS. This slip is supplemented by the plastic deformation of an amorphous component. In blends of high SEBS content, the role of deformation of an amorphous component by shear and flow increases markedly due to reduced overall crystallinity of these blends. In such blends an amorphous component includes a semicontinuous embedding of crystallites, and therefore, the deformation process is dominated by deformation mechanisms active in a more compliant amorphous phase. Consequently, with increasing the content of SEBS in the blend, the texture of the oriented blends changes from a single‐component (100)[001] texture to a texture with a strong fiber component in addition to a (100)[001] component. In blends with high content of SEBS, the crystalline lamellae of polyethylene do not undergo fragmentation up to the compression ratio of 6, while in blends with low and moderate content of SEBS, such lamellar fragmentation was detected. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1746–1761, 2000     

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends: correlation between Poisson ratio and adhesion

To gain more insight into the deformation behaviour of blends containing polystyrene (PS), low density polyethylene(IdPE) and a PSPE block copolymer, tensile tests have been performed with simultaneous volume measurements. Assuming that shearing does not give rise to volume changes, it is shown that, after yielding, crazing is the only deformation mechanism of blends with a low PE and PSPE block copolymer content. Shearing becomes important at relatively high copolymer concentrations. This is explained by the formation of a semi-continuous low-modulus phase. The decrease of the Poisson ratio with PE content in PSPE blends, as opposed to an increase if some block copolymer has been added to these blends, shows that the Poisson ratio is very sensitive to adhesion between the components. Toughness of PSPE blends is discussed in terms of concentrations of craze nuclei. Too few craze nuclei give rise to brittle failure: the resulting low number of crazes cannot take over much of the deformation of the matrix. Too many craze nuclei cause brittle failure because chances are high that some of the high number of crazes formed will combine to produce a fatal crack. Therefore high toughness is only obtained at intermediate craze nuclei concentrations. The concentration of craze nuclei is shown to be dependent on the number of dispersed particles and the adhesion between these particles and the matrix.     

Deformation behavior of HDPE/(PEC/PS)/SEBS blends

Immiscible blends of high density polyethylene (HDPE) and an amorphous glassy phase consisting of either pure polystyrene (PS) or a miscible blend of PS and a polyether copolymer (PEC) were compatibilized with various amounts of a styrene-hydrogenated butadiene block copolymer (SEBS). PEC is structurally similar to poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). Using a liquid displacement stress dilatometer, the volume change of samples during uniaxial mechanical straining was determined and related to the various modes of deformation. Blends were fabricated by both injection and compression molding. Miscible PEC and PS blends were found to undergo a craze to shear yielding transition between 40 and 60% PS, which occurred at higher PS concentrations as SEBS was added. Blends with a HDPE matrix and a dispersed glassy phase showed reduced volume dilatation on adding SEBS, indicating better interfacial adhesion between the incompatible blend components. Increases in the sample volume were substantially less in blends with a PEC/PS glassy phase instead of pure PS, suggesting more effective compatibilization by the SEBS copolymer in blends with PEC. This trend is presumed to stem from an exothermic heat of mixing between the PS endblocks of SEBS and the PEC-rich phases in the blend. Microscopic evidence of the improved adhesion and modes of deformation agrees with the results obtained by dilatometry. The volume dilatation of compression-molded materials do not seem to be similarly affected by the composition of the glassy phase which may reflect morphological differences between injection-and compression-molded blends.     

PS/SBR-g-PS共混物的力学性能和形态结构

采用种子乳液聚合技术在丁苯胶乳上接枝聚合苯乙烯 ,合成了一系列丁苯橡胶接枝聚苯乙烯共聚物 (SBR-g-PS)。将其与聚苯乙烯 (PS)树脂共混后 ,考察了 SBR-g-PS的组成 (SBR/ PS)对共混物的力学性能和形态结构的影响。结果发现 ,当 SBR/ PS为 6 7/ 33-5 0 / 5 0时 ,PS/ SBR-g-PS共混物表现出良好的综合力学性能 ,在 SBR-g-PS中随着接枝 PS的增多 ,像胶粒子在基体中的分散状况获得改善 ,在大橡胶颗粒中含有大量的 PS次级粒子。在外负载的作用下 ,共混物中的大橡胶颗粒引发了大量的银纹 ,吸收了断裂应变能 ,从而提高了材料的冲击韧性。     

Investigation of the rheological and mechanical properties of a polystyrene‐polyisobutylene‐polystyrene triblock copolymer and its blends with polystyrene

The rheological and mechanical properties of a polystyrene‐polyisobutylene‐polystyrene (SIBS) block copolymer containing 30 wt% polystyrene (PS) and its blends with PS (SIBS/PS) were investigated. Atomic Force Microscopy (AFM) was used to visualize the nanostructured phase morphology of the SIBS, which is responsible for the mechanical strength of this thermoplastic rubber. The order‐disorder transition (ODT) for the SIBS block copolymer was found to be above 250°C. SIBS/PS blends with 10–30 wt% PS showed improved moduli and tensile strengths. Blends containing up to 40 wt% PS behaved as thermoplastic elastomers. In the region of linear viscoelasticity the blends revealed pronounced non‐Newtonian behavior and enhanced elasticity. This paper also reports the role of this styrenic block copolymer in the impact modification of PS.     

Investigation of morphology formation in SBS block copolymer/homopolystyrene blends

Polymer blends comprising a polystyrene‐block‐polybutadiene‐block‐polystyrene (SBS) block copolymer and atactic homopolystyrene (hPS) were investigated using injection molded and solution cast samples. The morphology of the materials was studied by means of transmission electron microscopy (TEM) and scanning force microscopy (SFM). Dynamic mechanical analysis (DMA) was used to characterize the phase behavior and the morphology formation of the block copolymer as well as of the SBS/hPS blends. The glass transition temperatures seem to strongly depend on the homogeneity of the corresponding phases. A distinct difference was found between the morphologies of the blends prepared by different methods. While the SBS block copolymer always shows a lamellar morphology in injection molded or as‐cast samples, the injection molded blends show a disturbance in the morphology consisting of alternating layers. In contrast, in the case of as‐cast samples, added hPS forms polystyrene domains dispersed in a matrix of the pure block copolymer. Regarding the change in the glass transition temperature, in the effective volume and in the interfacial volume obtained from DMA curves, the morphology formation of the injection molded samples (pure SBS block copolymer and the corresponding blends) was investigated. Two different structural models for the blends are proposed. Polym. Eng. Sci. 44:1534–1542, 2004. © 2004 Society of Plastics Engineers.     

Phase behavior, morphology and interfacial structure in thermoset/thermoplastic elastomer blends of poly(propylene glycol)-type epoxy resin and polystyrene–b-polybutadiene

Thermoset/thermoplastic elastomer (TPE) blends of poly(propylene glycol) (PPG)-type epoxy resin (ER) and a diblock copolymer, polystyrene–b-polybutadiene (SB, with 30% styrene content), were prepared using 4,4′-diaminodiphenylmethane (DDM) as curing agent. The miscibility and thermal transition behavior of DDM-cured ER/SB blends were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The existence of three separate glass transitions, which are independent of the blend composition, indicates that SB is immiscible with DDM-cured ER. Neither the PS block nor the PB block exhibits miscibility with the cured ER. There exist three phases in the blends: a PS microphase, an ER-rich phase and a PB microphase. The phase structure and morphology of the ER/SB blends were studied using both scanning and transmission electron microscopy (SEM and TEM); a variety of morphologies were observed, depending on the blend composition. For the blends with 5 and 10 wt% SB, SB domains with irregular shapes and broadly distributed sizes are dispersed in a continuous cured ER matrix. For the blends with 20–60 wt% SB, interpenetrating bicontinuous phase structures are observed. For the blends with 70 wt% and more SB, a dispersion of cured ER particles in the SB matrix is obtained. The TEM observation showed that the two phases in the blends exhibit a good interfacial adhesion. The interfacial layer between the ER and SB phases varies from 100 to 300 nm for the blend with 20 wt% SB content, SB micelles are formed surrounding the SB domains in the ER matrix. Small-angle X-ray scattering (SAXS) experiments reveal that the SB diblock polymer still exhibits a lamellar microphase structure within the SB phase and the long spacing of lamellae nearly does not change in the blends. The SB diblock copolymer is microphase separated in the macroscopically phase separated ER/SB blends.     

Formation of phase structure and crystallization behavior in blends containing polystyrene–polyethylene block copolymers

The microphase separation structure in the molten state and the structure formation in crystallization from such ordered melt were investigated for the blends of polystyrene–polyethylene block copolymers (SE) with polystyrene homopolymer (PS) and polyethylene homopolymer (PE) and for the blends consisting of two kinds of SE with different copolymer compositions from each other, using synchrotron small-angle X-ray scattering techniques (SAXS). The copolymer compositions of SE block copolymers employed were 0.34, 0.58 and 0.73 wt. fraction of PE, and their melt morphologies were cylindrical, lamellar and lamellar, respectively. Macrophase separation or the morphology change in the melt occurred depending on the molecular weight and the blend composition, as reported so far. In crystallization from such macrophase-separated and microphase-separated melts, the melt morphology was completely kept for all the blends. Crystallization behavior was also investigated for the blends. The crystallization within the spherical and cylindrical domains surrounded by glassy PS was not observed for SE/PS blends. In the crystallization from the macrophase-separated melt, two exothermal peaks were observed in the DSC measurements, while a single peak was observed for other blends. For the blends with PS, the degree of crystallinity was depressed and the apparent activation energy of crystallization was high, compared to those for the corresponding neat SE. For SE/PE and SE/SE blends, those were changed depending on the blend composition.     

Morphology and micromechanical deformation behavior of styrene/butadiene‐block copolymers. I. Toughening mechanisms in asymmetric star block copolymers

Lamellae‐forming styrene/butadiene star block copolymers are studied to investigate the influence of morphology on micromechanical deformation mechanisms and mechanical properties by using transmission electron microscopy and tensile testing. A large homogeneous plastic deformation of polystyrene (PS) lamellae is found in styrene/butadiene star block copolymers on the basis of the new mechanism called thin‐layer yielding. This mechanism depends strongly on the thickness of the PS lamellae. At a critical thickness of PS lamellae of about 20 nm, a transition from thin‐layer yielding mechanism to a crazelike deformation was observed. These new deformation zones are similar to crazes with respect to their propagation perpendicular to direction of external stress and similar to shear bands with respect to an internal shear deformation component of the lamellae in the deformation zones. As a result of our investigations, the mechanical properties of star block copolymers can be understood in correlation with morphology and micromechanical deformation mechanisms. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 683–700, 2002     

Self‐assembled structures in blends of disordered and lamellar block copolymers: SAXS,SANS and TEM study

BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self‐assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS‐block‐dPMMA)₁/(dPS‐block‐PMMA)₂, were investigated using small‐angle X‐ray scattering, small‐angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution‐cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with M_n by D ～ M_n^2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene‐block‐polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single‐domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self‐assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene‐block‐polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry     

Deformation mechanisms and fracture toughness of polystyrene/high‐density polyethylene blends compatibilized by triblock copolymer

A dilatometric technique was used to explore the tensile deformation mechanisms of polystyrene (PS)/high‐density polyethylene (HDPE) blends compatibilized by a styrene–ethylene–butylene–styrene (SEBS) triblock copolymer. The volume change of the sample during a uniaxial tensile process was determined with two extensometers, and it provided useful information concerning the tensile deformation mechanism. A simple model was used in this study in order to obtain quantitative information on the separate contributions of several possible deformation modes to the total deformation. The results indicated that elastic deformation was the main deformation mode for PS. However, elastic deformation was the main mode of deformation prior to yielding for SEBS compatibilized PS/HDPE blends; thereafter the plastic deformations (including shear and crazing) appeared to dominate over the elastic deformation. Moreover, crazing was the main plastic deformation mode for the blend containing 20 wt % HDPE, and shear deformation became predominant when the HDPE content was further increased. Finally, the essential work concept was used to determine the fracture toughness of the typical ductile PS/HDPE/SEBS 10/80/10 blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2024–2033, 2000     

Instability of styrene/polystyrene/polybutadiene/polystyrene‐b‐polybutadiene emulsions that emulate styrene polymerization in the presence of polybutadiene

This article investigates the room temperature demixing of oil‐in‐oil emulsions containing styrene (St), polybutadiene (PB), a St‐butadiene star block copolymer (BC), and two polystyrene (PS) samples of different molecular weights and is a contribution toward a better understanding of the stability/instability of the reaction mixture in a bulk high‐impact polystyrene (HIPS) process close to the phase inversion. Twelve bulk prepolymerizations of St in the presence of PB were emulated, at 10%, 15%, and 20% conversion; and with constant grafting efficiencies. All the blends contained 6% in weight of butadiene units. After stirring the blends for 24 h, the decantation demixing process was monitored along 30 days, with daily measurement of the interface levels after appearance of a clear interface. For some of the isolated phases, their unswollen morphologies were observed by transmission electron microscopy. All the isolated phases exhibited macrophase separation into homopolymer‐ and copolymer‐rich macrodomains with lamellar microdomains. The BC showed a greater affinity toward the PS‐rich phase. The separation of an independent BC‐rich phase in the blends containing the high molar mass PS and at high grafting efficiencies, modifies the idea of the graft‐ or BC molecules located at the interface of large PS‐rich and PB‐rich phases. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Temperature-composition phase diagrams of binary blends of block copolymer and homopolymer

The temperature-composition phase diagrams for six pairs of diblock copolymer and homopolymer are presented, putting emphasis on the effects of block copolymer composition and the molecular weight of added homopolymers. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers having lamellar or spherical microdomains, a polystyrene-block-polybutadiene (SB diblock) copolymer having lamellar microdomains, and a series of polystyrene (PS), polyisoprene (PI), and polybutadiene (PB) were used to prepare SI/PS, SI/PI, SB/PS, and SB/PB binary blends, via solvent casting, over a wide range of compositions. The shape of temperature-composition phase diagram of block copolymer/homopolymer blend is greatly affected by a small change in the ratio of the molecular weight of added homopolymer to the molecular weight of corresponding block (M_H,A/M_C,A or M_H,B/M_C,B) when the block copolymer is highly asymmetric in composition but only moderately even for a large change in M_H,A/M_C,A ratio when the block copolymer is symmetric or nearly symmetric in composition. The boundary between the mesophase (M₁) of block copolymer and the homogeneous phase (H) of block copolymer/homopolymer blend was determined using oscillatory shear rheometry, and the boundary between the homogeneous phase (H) and two-phase liquid mixture (L₁+L₂) with L₁ being disordered block copolymer and L₂ being macrophase-separated homopolymer was determined using cloud point measurement. It is found that the addition of PI to a lamella-forming SI diblock copolymer or the addition of PB to a lamella-forming SB diblock copolymer gives rise to disordered micelles (DM) having no long-range order, while the addition of PS to a lamella-forming SB diblock copolymer retains lamellar microdomain structure until microdomains disappear completely. Thus, the phase diagram of SI/PI or SB/PB blends looks more complicated than that of SI/PS or SB/PS blends.