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     

Influence of Phase Separation Behaviour on Toughness of Compression Moulded SBS Star Block Copolymer/Polystyrene Blends

The influence of homopolymer molecular weight and compression moulding on morphology formation and deformation behaviour of binary blends of polystyrene-polybutadiene based star block copolymer and polystyrene (PS) homopolymer was investigated. The samples used were a polystyrene-(polystyrene-co-polybutadiene)-polystyrene (S-S/B-S) star block copolymer and anionically prepared polystyrene (aPS). The techniques used were transmission electron microscopy (TEM) and uniaxial tensile testing. A wide range of segregation behaviour was observed depending on the ratio of the length of aPS chains relative to that of corresponding outer blocks of the block copolymer. For the first time, the formation of macrophase-separated ‘droplet-like’ morphology has been reported, which endows the block copolymer/polystyrene blends with higher toughness. The mechanical properties of blends are discussed in the light of micromechanical processes of deformation. The micromechanical mechanisms and their dependence with inter domain distance are similar to the mechanisms found in rubber network toughened systems.     

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.     

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.     

Towards quantification of butadiene content in styrene-butadiene block copolymers and their blends with general purpose polystyrene (GPPS) and the relation between mechanical properties and NMR relaxation times

The properties of styrene-butadiene-styrene (SBS) block copolymers do not only depend on the butadiene content and the degree of polymerisation but also on their chain architecture. In this contribution we present the results of a low-field time domain (TD) NMR study in which the transverse relaxation behaviour of different SBS block copolymers was analysed and correlated with findings from mechanical testing on pure and blended materials and transmission electron microscopy data which provide information on the microphase separation.The results indicate that while a straightforward determination of the butadiene content as in blended materials like ABS is not possible for these materials, the TD-NMR results correlate quite well with the mechanical performance of blends from SBS block copolymers with general purpose polystyrene (GPPS), i.e. industrial grade homopolymer polystyrene. Temperature-dependent experiments on pure and blended materials revealed a slight reduction in the softening temperature of the GPPS fraction in the blends.     

Selective control over the lamellar thickness of one domain in thin binary blends of block copolymer films

Thin binary blends of poly(styrene‐b‐methyl methacrylate) (PS‐PMMA) block copolymers in films where the lamellar thickness of one domain is controlled while preserving the thickness of the other domain were demonstrated without microphase separation. One of the block copolymers used here was short and symmetric, and the other was long and asymmetric; the molecular weights of the PMMA block chains in the constituents were similar. A random copolymer brush was introduced and film thickness and composition of brush were adjusted to induce perpendicular orientation in thin film. As the blend composition of the long asymmetric block copolymer increased, the PS lamellar thickness increased from 15.8 to 25.1 nm, whereas the PMMA lamellar thickness remained constant at approximately 14 nm (the thickness decreased slightly from 14.0 to 13.3 nm). The domain spacing behavior in thin film was consistent in the bulk. These results were compared with the Birshtein, Zhulina, and Lyatskaya model and the theories for pure block copolymers in the strong segregation limit and in the intermediate segregation regime. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1393–1399     

Morphological mapping and analysis of poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] and its clay nanocomposites by atomic force microscopy

Atomic force microscopy was successfully applied for comprehensive nanoscale surface and bulk morphological characterization of thermoplastic elastomeric triblock copolymers: poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) having different block lengths and their clay based nanocomposites. Commercially available Cloisite®20A and octadecyl (C₁₈) ammonium ion modified montmorillonite clay (OC) prepared in our laboratory by cation exchange reaction were used. The phase detected images in the tapping mode atomic force microscopy exhibited a well‐ordered phase separated morphology consisting of bright nanophasic domains corresponding to hard component and darker domains corresponding to softer rubbery ethylene‐co‐butylene (PEB) lamella for all the neat triblock copolymers. This lamellar morphology gave a domain width of 19–23 nm for styrenic nanophase and 12–15 nm for ethylene‐co‐butylene phase of SEBS having end to mid block length ratio of 30:70 and block molecular weights of 8800–41,200–8800. On increasing the ratio of block lengths of the polymer matrix and the selectivity of the solvent toward the blocks used for casting, the morphological features of the resultant films altered along with change in domain thickness. The phase images showed position and distribution of the brightest clay stacks in the dark‐bright contrast of the base matrix of the nanocomposite. Exfoliated and intercalated‐exfoliated morphology obtained in the case of Cloisite®20A and OC‐based SEBS nanocomposites, respectively, is further supported by X‐ ray diffraction and transmission electron microscopy studies. The lamellar thickness of the soft phases widened to 50–75 nm, where the layered clay silicates (40–54 nm in length and 4–17 nm in width) were embedded in the soft rubbery phases in the block copolymeric matrix of the nanocomposite. The marginally thicker width of the hard styrenic phases and slightly shrinked width of the soft rubbery lamella can be observed from the regions where no nanofiller is present. Distinct differences in bulk morphologies of the nanocomposites prepared in the melt and the solution processes were obtained with nanocomposites. The presence of clay particles was evident from the almost zero pull‐off and snap‐in force in the force‐distance analysis of SEBS based nanocomposite. This analysis also revealed stronger tip interaction resulting in highest contact and adhesive forces with the softer PEB region relative to the harder PS region. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 52–66, 2007     

New methodology for synthesizing polyolefinic graft block copolymers and their morphological features

This paper describes a new synthetic route for polyolefinic graft block copolymers by adopting coupling reaction between terminally hydroxylated polyolefins and maleic anhydride grafted polyolefins. Terminally hydroxylated polypropylene (PP-OH) was coupled with maleic anhydride modified polyethylene (PE-g-MAH) and such ethylene-propylene random copolymer (EPR-g-MAH) to give polyolefinic graft block copolymers (PE-g-PP and EPR-g-PP, respectively). The formation of PE-g-PP was confirmed by enhancement on molecular weight and it brought about distinctive decrease in size of dispersed domain in its phase separation morphology. Occurrence of coupling reaction to give EPR-g-PP was indicated by extreme decrease in its solubility to n-decane and it led to unique morphology demonstrating lamella microstructure that had never been reported for a comparable polyolefin composite.     

Organizing thermodynamic data obtained from multicomponent polymer electrolytes: Salt‐containing polymer blends and block copolymers

The objective of this review is to organize literature data on the thermodynamic properties of salt‐containing polystyrene/poly(ethylene oxide) (PS/PEO) blends and polystyrene‐b‐poly(ethylene oxide) (SEO) diblock copolymers. These systems are of interest due to their potential to serve as electrolytes in all‐solid rechargeable lithium batteries. Mean‐field theories, developed for pure polymer blends and block copolymers, are used to describe phenomenon seen in salt‐containing systems. An effective Flory–Huggins interaction parameter, χ_eff , that increases linearly with salt concentration is used to describe the effect of salt addition for both blends and block copolymers. Segregation strength, χ_effN , where N is the chain length of the homopolymers or block copolymers, is used to map phase behavior of salty systems as a function of composition. Domain spacing of salt‐containing block copolymers is normalized to account for the effect of copolymer composition using an expression obtained in the weak segregation limit. The phase behavior of salty blends, salty block copolymers, and domain spacings of the latter systems, are presented as a function of chain length, composition and salt concentration on universal plots. While the proposed framework has limitations, the universal plots should serve as a starting point for organizing data from other salt‐containing polymer mixtures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1177–1187     

Molecular design of multicomponent polymer systems XIX: Stability of cocontinuous phase morphologies in low-density polyethylene–polystyrene blends emulsified by block copolymers

Polyethylene–polystyrene blends containing small amounts of polyethylene (20 wt %) display a cocontinuous phase morphology that is very unstable in the absence of an emulsifier. The kinetics of coalescence at high temperature is therefore very sensitive to differences in the interfacial activity of added polymeric emulsifiers. The morphology of blends added with a pure or a tapered hydrogenated polybutadiene-b-polystyrene block copolymer is investigated as a function of annealing time at 180°C. Various image treatments (standard granulometry, opening size granulometry distribution, and multiscaling analysis) were used to quantify the morphological evolution of these blends. The results clearly demonstrate that the tapered block copolymer is definitely more efficient than the corresponding pure diblock for stabilizing the cocontinuous structure of these blends. The differential behavior is assumed to results from differences in the tendency of the two copolymers to segregate and form their own domains. © 1995 John Wiley & Sons, Inc.     

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.     

Application of ESCA to polymer chemistry. VIII. Surface structures of AB block copolymers of polydimethylsiloxane and polystyrene

The surface morphology of a number of films of AB block copolymers of polydimethylsiloxane and polystyrene was examined by ESCA and contact angle measurements. In all cases the immediate surface is shown to consist of an essentially pure polydimethylsiloxane component. By comparing the intensities of elastic peaks corresponding to photoionizations from core levels without energy loss for polydimethylsiloxane and polystyrene with those for the block copolymers and by consideration of shake-up phenomena specific to the polystyrene component, an estimate of the thickness of the polydimethylsiloxane outer layer of the latter may be obtained. This is shown to vary between ～13 and 40 Å, depending on the method of formation of copolymer film.     

The effect of hard and soft segment composition and molecular architecture on the morphology and mechanical properties of polystyrene-polyisobutylene thermoplastic elastomeric block copolymers

This paper reports the effects of hard (polystyrene, PS) and soft (polyisobutylene, PIB) segment composition and the molecular architecture (linear versus star, PS and PIB block length) on the morphology and mechanical properties of polystyrene/polyisobutylene (SIBS) block copolymers synthesized by living carbocationic polymerization. Atomic force microscopy, dynamic mechanical thermal analysis and tensile testing verified the phase-separated nature of the block copolymers, which behaved as thermoplastic elastomers (TPEs). The morphology of these TPEs is similar to polydiene-based TPEs, and is defined by the soft/hard segment composition. Interestingly, topology (linear vs star) did not have a major influence on morphology. Tensile testing showed that for both linear and three-arm star block copolymers, the modulus and tensile strength increased while elongation at break decreased with higher PS content. However, three-arm star block copolymers showed larger moduli than their linear homologues with similar PS content and PIB arm length, indicating the influence of molecular architecture on mechanical properties. These results might serve as a foundation for macromolecular engineering design for optimizing properties.     

增容聚苯乙烯共混物的研究进展

综述了增容聚苯乙烯与聚乙烯、聚丙烯、聚酰胺共混物的研究进展。不同共混物采用不同的增容剂,可使增容聚苯乙烯共混物改善分散相尺寸、界面相互作用与粘结,达到提高共混物的力学性能的目的。增容效果与增容剂的类型、用量和分子结构有关。     

Effect of selected structural parameters of styrene–butadiene block copolymers on their compatibilization efficiency in polystyrene/polybutadiene blends

The effects of the block length and block number of linear styrene–butadiene (S–B) block copolymers on their compatibilization efficiency in blending polystyrene with polybutadiene were studied. For this purpose, two sets of model S–B copolymers and both homopolymers were prepared by anionic polymerization. Diblocks, triblocks, or pentablocks of S–B copolymers were blended with these homopolymers, and the structures and some end‐use properties of the blends were determined. The supramolecular structure (determined by small‐angle X‐ray scattering), morphology (determined by transmission and scanning electron microscopy), and stress‐transfer characteristics (impact and tensile strengths) of the blends were chosen as criteria for the compatibilization efficiency of the copolymers used. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2612–2623, 2002     

Synthesis and micellar behavior of poly(vinyl alcohol-<Emphasis Type="Italic">b</Emphasis>-styrene) copolymers containing PVA blocks with different syndiotacticity

Poly(vinyl alcohol-b-styrene) (poly(VA-b-St)) diblock copolymers with different syndiotacticity of poly(vinyl alcohol) (PVA) block were synthesized via consecutive telomerization, atom transfer radical polymerization, and saponification. These amphiphilic block copolymeric micelles were prepared by dialysis against water. Dynamic light scattering and transmission electron micrograph measurements confirmed the formation of a micelles, and the size of a micelle was less than 100 nm and increased with the molecular weight of polystyrene (PS) block. From the fluorescence emission spectrum measurements using pyrene as a fluorescence probe, the copolymers formed micelles with critical micelle concentration (CMC) in the range of 0.125–4.47 mg/l. The CMC values increase with decrease of the molecular weight of the PS block and increase of the syndiotacticity of PVA block. Kinetic stability study of micelles showed increased stability for block copolymers containing PVA block with higher syndiotacticity.     

Effect of mixing conditions on the morphology and properties of polystyrene/polyethylene blends compatibilized with styrene–butadiene block copolymers

The effect of mixing conditions on the morphology, molten‐state viscoelastic properties, and tensile impact strength of polystyrene/polyethylene (80/20) blends compatibilized with styrene–butadiene block copolymers containing various numbers and lengths of blocks was studied. Under all mixing conditions, an admixture of a styrene–butadiene block copolymer led to a finer phase structure and to an increase in the dynamic viscosity, storage modulus, and tensile impact strength. The effects were stronger for S–B diblock with a short styrene block than for S–B–S–B–S pentablock with long styrene blocks (where S represents styrene and B represents butadiene). For all blends mixed longer than 2 min, the mixing time had only a small effect on their morphology and properties. Surprisingly, the localization of S–B diblock copolymers was strongly dependent on the rate of mixing. The mixing rate had a nonnegligible effect on the viscoelastic properties of the compatibilized blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 609–622, 2003     

Side chain crystallization in microphase-separated poly(styrene-block-octadecylmethacrylate) copolymers

The crystallization behavior of two microphase-separated poly(styrene-b-octadecylmethacrylate) block copolymers with lamellar and cylindrical morphology is studied by DSC. The findings are compared with results for a polyoctadecylmetharcylate (PODMA) homopolymer. The situation in the block copolymers is characterized by the occurrence of a confined side chain crystallization in small PODMA domains surrounded by a glassy polystyrene phase. The strength of confinement effects depends significantly on the block copolymer morphology. The crystallization behavior of PODMA lamellae with a thickness of about 10 nm is only slightly affected and similar to the situation in the homopolymer. In cylindrical PODMA domains with a diameter of about 10 nm strong confinement effects are observed: the degree of crystallinity is 50% reduced and the crystallization kinetics slows down. The Avrami coefficients change from n≈3 for the homopolymer and PODMA lamellae to n≈1 for PODMA cylinders. This observation indicates one-dimensional growth in small cylinders or a change from heterogeneous to homogeneous nucleation. Pros and cons of both approaches are discussed. A speculative picture explaining qualitatively the differences in the crystallization behavior of PODMA lamellae and cylinders in a glassy polystyrene matrix is presented.     

Study of the surface morphology of polyisobutylene-based block copolymers by atomic force microscopy

This paper reports the investigation of the nanostructured surface morphology of linear polystyrene-block-polyisobutylene-block-polystyrene (SIBS) triblock copolymers and novel arborescent SIBS block copolymers by Atomic Force Microscopy (AFM) in the tapping mode. Thin films spin coated from toluene onto silicon wafers were studied. The nanostructured morphology of the block copolymers varied with the hard polystyrene (PS) and soft polyisobutylene (PIB) segment composition, ranging from spherical to lamellar nanometer-sized discreet PS phases dispersed in a continuous PIB matrix. Annealing the samples resulted in well developed/ordered structures. The arborescent blocks had irregularly distributed PS phases in the PIB matrix. Annealing had a dramatic effect on the morphology which still remained irregular. Three-dimensional AFM image and section analysis indicated the presence of a height difference between PIB (high-lying plateaus or hills) and PS (low-lying plateaus or valleys) in the block copolymers, which became more prominent during annealing. It is theorized that the rubbery PIB chains are able to relax, thereby protruding from the surface, anchored by the physically crosslinked PS phases.