Block Copolymer Blends Research Articles

Crystallization behavior of dry‐brush PEO‐PS block copolymer and PEO homopolymer blend

AbstractThe crystallization behavior of semicrystalline PEO homopolymer/triblock PS‐PEO‐PS copolymer blend system, which exhibited “Dry‐Brush” in the melt. A symmetric polystyrene–poly(ethylene oxide)–polystyrene triblock copolymer was blended with PEO homopolymer (h‐PEO) having the same molecular weight as that of the PEO block in the copolymer. Considering the composition of the blend (Wps ≥ 0.8), PEO spheres were formed in the blend. Because of the dry‐brush phase behavior of this blend, h‐PEO added was localized in the PEO microdomains, which increases the domain size without changing the microdomain morphology. The crystallization of PEO block was confined within the microdomains and the crystallization temperature was about 60°C lower than normal. Self‐seeding tests were performed to clarify the nucleation mechanism of the blend. Because the droplets size varies greatly, multicrystallization peaks were witnessed in the self‐seeding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Domain Size Control in Self-Assembling Rod−Coil Block Copolymer and Homopolymer Blends

The addition of homopolymers to a self-assembling rod−coil block copolymer is demonstrated to be a flexible route toward domain size control. Molecular weight matched rod-like homopolymers interdigitate with the rod-blocks within their respective lamellae. As a result of the interdigitation, the coil blocks must rearrange to occupy more interfacial area resulting in an unprecedented decrease in domain spacing with increasing rod homopolymers. Conversely coil homopolymers were locally solubilized within the coil microdomain resulting in an increase of domain spacing with increasing coil homopolymers. The mechanisms of homopolymers solubilization are in qualitative agreement with predictions made by self-consistent mean-field theory (SCFT) calculations.

Self‐Assembled Structures in Block Copolymer Blends: SAXS, SANS and TEM Study

AbstractPhenomena associated with the order‐disorder transition, microdomain morphology and phase behavior of a deuterated block copolymer (BCP) blend I/II (where I is dPS‐block‐dPMMA and II is dPS‐block‐PI) were studied by SAXS, SANS and TEM. The studied, almost symmetric, copolymers differ essentially in microdomain morphology. One of them (I) is in disordered microdomain state, while the other (II) displays lamellar morphology at ordinary temperatures. Self‐assembled structures in blends were investigated as a function of concentration of the added microphase‐separated copolymer and temperature. The ODT positions were located in all the blends, the position of ODT depending only slightly on the concentration of the ordered copolymer. A systematic increase in long period D of the lamellar phase is observed with the growing content of the disordered copolymer. The evaluation of TEM shows the gradual diminishing of macrophase separated regions of disordered copolymer I with growing content of the lamellar copolymer II.magnified image

Preparation of HDPE/SEBS‐g‐MAH and its effect on mechanical properties of HDPE/wood flour composites

AbstractIn this article, high density polyethylene/styrene‐ethylene‐butylene‐styrene block copolymer blends (HDPE/SEBS) grafted by maleic anhydride (HDPE/SEBS‐g‐MAH), which is an effective compatibilizer for HDPE/wood flour composites was prepared by means of torque rheometer with different contents of maleic anhydride (MAH). The experimental results indicated that MAH indeed grafted on HDPE/SEBS by FTIR analysis and the torque increased with increasing the content of maleic anhydride and dicumyl peroxide (DCP). Styrene may increase the graft reaction rate of MAH and HDPE/SEBS. When HDPE/SEBS MAH was added to HDPE/wood flour composites, tensile strength and flexural strength of composites can reach 25.9 and 34.8 MPa in comparison of 16.5 and 23.8 MPa (without HDPE/SEBS‐g‐MAH), increasing by 157 and 146%, respectively. Due to incorporation of thermoplastic elastomer in HDPE/SEBS‐g‐MAH, the Notched Izod impact strength reached 5.08 kJ m−2, increasing by 145% in comparison of system without compatibilizer. That HDPE/SEBS‐g‐MAH improved the compatibility was also conformed by dynamic mechanical measurement. Scanning electron micrographs provided evidence for strong adhesion between wood flour and HDPE matrix with addition of HDPE/SEBS‐g‐MAH. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Blends of Poly(methacrylate) Block Copolymers with Photoaddressable Segments

The paper presents the synthesis of azobenzene-functionalized block copolymers based on a poly(methyl methacrylate) (PMMA) segment and an azobenzene-functionalized poly(hydroxyethyl methacrylate) segment, and a basic study of blending these block copolymers with homopolymers is given. Two diblock copolymers, prepared via different routes, were synthesized by a living anionic polymerization followed by a polymer analogous reaction to attach the azobenzene side groups. Self-assembly of the block copolymers resulted in phase-separated morphologies on the nanometer scale. The photoaddressable azobenzene segments are dispersed in the PMMA matrix and locally confined. Special focus is given to the preparation and characterization of block copolymer blends with PMMA homopolymer in order to dilute the phase-separated azobenzene morphology and reduce the optical density while maintaining the confinement. The block copolymer blends were characterized with respect to their morphology and initial holographic experiments were performed.

Self‐Assembled Structures in Blends of Block Copolymer A‐block‐B with Homopolymer A: SAXS and SANS Study

AbstractSummary: The study describes the investigation of the microphase‐separated morphology of a block copolymer A‐block‐B with the parent homopolymer A, where A is polystyrene and A‐block‐B is poly(perdeuterated styrene)‐block‐poly(methyl methacrylate) (dPS‐block‐PMMA). The microdomain morphology and phase behavior in blends of dPS‐block‐PMMA with polystyrene of $\overline M _{\rm w}$ = 8 000 and 35 000 were investigated. Binary blends of the diblock copolymer and homopolymers were prepared with various amounts of homopolymers. The criterion for “wet and dry brush” taking into account different solubilization of homopolymer has been applied to explain the changes in microdomain morphology during the self‐assembling process. magnified image

Preparation and Properties of Polystyrene/SEBS Blends with Compositional Gradients in Their Sheet Direction

AbstractThere have been a few reports that discussed polymer blends with compositional gradient in their sheet directions. Thus, we discussed the preparation of the graded polystyrene(PS)/styrene‐hydorogenated butadiene‐ styrene block copolymer(SEBS) blend with compositional gradient in their sheet directions, by applying of the solution‐diffusion method. Then, the hardness on the air side surface of the graded blend gradually increased with shifting the measured point from the edge containing lowest PS content. All of the areas, into which the graded blend sheet was divided, were almost equal in length, when total elongation was 6.6 mm. However, the length of the area became longer at the larger SEBS content, when the total elongation was 175 mm. The ratio of the length of the area to that in lowest SEBS content increased gradually with increasing of SEBS content, when the total elongation became over 50 mm. It was considered that this phenomenon occurred, because of the compositional gradient in the PS/SEBS graded blend.

Efficient light emitting diodes from ternary blends of PPV‐based copolymers

AbstractLight emitting diodes (LEDs) were prepared using ternary blends of block copolymers emitting in the blue (I and II) and green (III) regime. These blends were studied in terms of their absorbance, photoluminescence (PL), and electroluminescence (EL) spectra. The PL spectra in dilute solution and in the solid state were compared. Förster energy transfer from I and II to III was studied in the solid state. The EL device made using a ternary blend with the ratio (1 : 1 : 1) showed the highest EL quantum efficiency. Differential scanning calorimetry (DSC) measurements have been made to investigate the phase separation in these copolymer blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2509–2511, 2006

Neutron Reflection Studies on Lamellar Microphase-Separated Structures of Two-Component Block Copolymers with Composition Distribution

Segmental distribution of polystyrene blocks in lamellar microphase-separated poly(styrene- block-2-vinylpyridine) (SP) with wide composition distribution was investigated by neutron reflectivity measurements using deuterium-labeled polymers. Block copolymers with wide composition distribution were produced by mixing three monodispersed parent block copolymers, which were synthesized by an anionic polymerization method to have the same total molecular weight but with different volume fractions. The block copolymer blends whose overall S/P ratio is 0.5/0.5 were found to form a uniform lamellar structure, where lamellae were highly oriented along the direction parallel to the film surface and the interfacial thickness was evaluated as 40 Å. It was clarified that a shorter block chain in the microdomain is localized at the domain boundary, while a longer one has a peak at the center of microdomain in its segmental distribution profile.

Formation of Polyolefin‐block‐polystyrene Block Copolymers on Phenoxyimine Catalysts

AbstractSummary: PE‐block‐PS and P(E‐co‐P)‐block‐PS block copolymers were synthesised via sequential monomer addition during homogeneous polymerisation on various phenoxyimine catalysts. One phenoxyimine catalyst was tailored to produce high molecular weight block copolymers containing both, polyolefin and polystyrene segments. According to chromatographic analysis and TEM morphology studies, blends of block copolymers and PE homopolymers [or P(E‐co‐P), respectively] were formed. The direct olefin/styrene block copolymer synthesis on phenoxyimine catalysts represents an attractive, new one‐pot route to styrenic block copolymers which are commercially prepared by anionic styrene/diene block copolymerisation followed by hydrogenation. magnified image

Archimedean Tiling Structures from ABA/CD Block Copolymer Blends Having Intermolecular Association with Hydrogen Bonding

Self-assembled phase structures of ABA/CD block copolymer blends were investigated. A pair of poly(2-vinylpyridine-block-isoprene-block-2-vinylpyridine) (PIP-91) whose molar ratio of polyisoprene and poly(2-vinylpyridine) is 0.93:0.07 and poly(styrene-block-4-hydroxystyrene) (SH-91) whose molar ratios is 0.86:0.14 were used as samples. Two component polymers, i.e., poly(2-vinylpyridine) and poly(4-hydroxystyrene), are confirmed to form complex via hydrogen-bonding interaction by 1H nuclear magnetic resonance (NMR) analysis. Structural observation using transmission electron microscopy (TEM) reveals that PIP-91/SH-91 blends form new regular three-phase cylindrical structures having I, S, and P/H phases, the third one being conformed of intermolecular complex from P and H chains. The cross sections of the structures show periodic two-dimensional tiling patterns from regular polygons, which must be due to “bridged” PIP chains. Consequently, new mesoscopic Archimedean tiling patterns, that is, (33.42) and (3.4.6.4), have been formed from this blend system.

Strain Field Analysis and Kinetics of Crack Propagation of Binary Triblock Copolymer Blends

AbstractSummary:The crack toughness behaviour of binary styrene‐butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer (LN3) and a thermoplastic elastomer (LN4) with different molecular architecture was studied using essential work of fracture (EWF) concept and was correlated to the morphological features from transmission electron microscopy (TEM). An increase in the crack toughness behaviour between 60 and 80 wt.‐% LN3 has been observed and is attributed to a change from cylindrical to lamellar morphology. The time‐resolved crack propagation studies have offered new dimensions to understand the kinetic aspects of fracture behaviour while the strain field analysis has explained the time‐dependent deformation behaviour to characterise the time dependence of the strain energy dissipation modes.Load‐displacement diagrams of non essential work of fracture values of LN3/LN4 blends.magnified imageLoad‐displacement diagrams of non essential work of fracture values of LN3/LN4 blends.

Boundary conditions for equilibrating incommensurate periodic patterns

Simulation of periodic patterns often suffer from artifacts due to incommensurability of the intrinsic length scale and the system size. We introduce a simple numerical scheme to avoid this problem in finding equilibrium domain morphologies from a Ginzburg-Landau-type free energy. In this scheme, the boundary values are determined only by the local equilibrium condition at the adjacent bulk sites. The scheme is especially advantageous in equilibrating patterns that have two or more characteristic lengths. We demonstrate it using a model of lamellar-lamellar coexistence in block copolymer blends.

Directed Assembly of Block Copolymer Blends into Nonregular Device-Oriented Structures

Self-assembly is an effective strategy for the creation of periodic structures at the nanoscale. However, because microelectronic devices use free-form design principles, the insertion point of self-assembling materials into existing nanomanufacturing processes is unclear. We directed ternary blends of diblock copolymers and homopolymers that naturally form periodic arrays to assemble into nonregular device-oriented structures on chemically nanopatterned substrates. Redistribution of homopolymer facilitates the defect-free assembly in locations where the domain dimensions deviate substantially from those formed in the bulk. The ability to pattern nonregular structures using self-assembling materials creates new opportunities for nanoscale manufacturing.

Controlling the size of nanostructures in thin films via blending of block copolymers and homopolymers

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.

Polypropylene/talc/SEBS (SEBS-g-MA) composites. Part 1. Structure

Abstract Isotactic polypropylene/styrenic rubber block copolymer blends (iPP/SRBC) as well as the iPP/talc/SRBC composites with 12 vol% of aminosilane surface treated talc were studied by optical and scanning electron microscopy, and by wide angle X-ray diffraction. Structure of polypropylene blends and composites was investigated as a function of poly(styrene-b-ethylene-co-butylene-b-styrene) triblock copolymer (SEBS) and the SEBS grafted with maleic anhydride (SEBS-g-MA) content in the range from 0 to 20 vol% as elastomeric components. Both copolymers (SEBS and SEBS-g-MA) affected the iPP spherulite size in blends by nucleation and solidification effects during crystallization. Talc crystals, homogeneously incorporated in the iPP matrix, accommodated mostly plane-parallel to the surface of the samples and strongly affected crystallization process of the iPP matrix disturbing well-developed spherulitic morphology of polypropylene. Both, SEBS and SEBS-g-MA block copolymers, encapsulated talc crystals, thus forming core–shell morphology in significantly higher extent than the poly(styrene-b-butadiene-b-styrene) triblock (SBS) and the poly(styrene-b-ethylene-co-propylene) diblock copolymer (SEP) in iPP/talc composites, studied previously. SEBS-g-MA encapsulated and disorientated plane-parallel talc crystals more significantly than the SEBS block copolymer.

Polypropylene/talc/SEBS (SEBS-g-MA) composites. Part 2. Mechanical properties

Isotactic polypropylene/styrenic rubber block copolymer blends (iPP/SRBC) as well as the iPP/talc/SRBC composites with 12 vol.% of aminosilane surface treated talc were studied by the measurement of mechanical properties (tensile properties and notched impact strength). Mechanical properties and their relation with the structure of polypropylene blends and composites were investigated as a function of poly(styrene-b-ethylene-co-butylene-b-styrene) triblock copolymer (SEBS) and the SEBS grafted with maleic anhydride (SEBS-g-MA) content in the range from 0 to 20 vol.% as elastomeric components. Elongation at yield of the iPP/talc/SEBS-g-MA composites and impact strength of the iPP/talc/SEBS composites show synergistic effect at high elastomer content (20 vol.%). Higher molecular weight (and consequently higher viscosity, elasticity and impact strength) of thicker SEBS layers around highly oriented talc crystals and higher miscibility or interactivity of SEBS than SEBS-g-MA with iPP chains seem to contribute to enormous impact strength of the iPP/talc/SEBS composites. On the other side, a higher extent of encapsulation and disorientation of talc crystals by the SEBS-g-MA than by SEBS copolymer, and lower molecular weight of the SEBS-g-MA than SEBS copolymer may contribute to higher elongation at yield of the iPP/talc/SEBS-g-MA composite.

Morphology and mechanical properties of binary triblock copolymer blends

AbstractThe influence of the morphology on the mechanical properties of binary styrene–butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer and a thermoplastic elastomer (TPE) with different molecular architectures was studied with bulk samples prepared from toluene. Both block copolymers contained SB random copolymer middle blocks, that is, the block sequence S–SB–S. The two miscible triblock copolymers were combined to create a TPE with increased tensile strength without a change in their elasticity. The changes in the equilibrium morphology of the miscible triblock copolymer blends as a function of the TPE content (lamellae, bicontinuous morphology, hexagonal cylinders, and worms) resulted in a novel morphology–property correlation: (1) the strain at break and Young's modulus of blends with about 20 wt % TPE were larger than those of the pure thermoplastic triblock copolymer; (2) at the transition from bicontinuous structures to hexagonal structures (∼35 wt % TPE), a change in the mechanical properties from thermoplastic to elastomeric was observed; and (3) in the full range of wormlike and hexagonal morphology (60–100 wt % TPE), elastomeric properties were observed, the strength greatly increasing and high‐strength elastomers resulting. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 429–438, 2005

Density Functional Theory for Block Copolymer Melts and Blends

We derive an expression for the free energy of the blends of block copolymers expressed as a functional of the density distribution of the monomer of each block. The expression is a generalization of the Flory-Huggins-de Gennes theory for homo polymer blends, and also a generalization of the Ohta-Kawasaki theory for the melts of diblock copolymers. The expression can be used for any blends of homopolymers and block copolymers of any topological structure. The expression gives a fast and stable computational method to calculate the micro and macro phase separation of the blends of homopolymers and block copolymers.

Proximity Effects in Self-Organized Binary Particle–Block Copolymer Blends

Dependent on the surface chemistry of gold nanocrystals of equal metal core size, two morphological types of self-organized block copolymer-particle blends are observed: (1) the segregation of the nanocrystals to the interfacial areas or (2) the preferential uniform distribution within one of the respective polymer domains. The confinement of the nanocrystals to the narrow interfacial regions of the microstructure in type one blends results in high local particle filling fractions and gives rise to electromagnetic coupling upon light irradiation, accompanied by a pronounced increase in absorbance.