Block-polystyrene Triblock Copolymer Research Articles

Synthesis and properties of styrenic triblock copolymers with dual structural asymmetry via RAFT emulsion polymerization

The polystyrene-block-poly(n-butyl acrylate)-block-polystyrene (PSt-b-PBA-b-PSt, SBAS) triblock copolymers (TBCPs) with dual structural asymmetry were synthesized via a reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. The dual structural asymmetry contained two asymmetric outer PSt blocks and a single short ionic block on one chain end while the SBAS TBCPs had the almost same molecular weight (~100 kDa) and composition (~70 wt% of PSt and ~30 wt% of PBA) excluding the short ionic block. The dual structural asymmetry with a synergistic effect was designed by locating the long PSt block near the short ionic block that was derived from ionic macromolecular RAFT agent. With the SBAS TBCPs having microphase separation structure, the structural asymmetry of two outer PSt blocks tailored the interaction of PSt and PBA blocks, further leading to the change of static tensile and dynamic mechanical properties, and rheology. Structural asymmetry will provide an alternative to tailor-made properties of TBCPs.

Tailoring Cation Solvation in Electrode-Decoupled Redox Flow Batteries Significantly Enhances Capacity and Cycle Life

Electrode-decoupled redox flow batteries (ED-RFBs) employ disparate cationic actives in the anolyte and catholyte, significantly expanding the chemical design space for flow batteries. Crossover induced capacity fade in such systems can be mitigated or eliminated by the use of highly permselective anion exchange membranes (AEMs) as separators. Herein, we show that tailoring the solvation shell around the cationic actives aids in significantly reducing crossover and hence capacity fade. A model V-Ce ED-RFB was developed utilizing this paradigm and demonstrated a 30% enhancement in practical volumetric capacity1. By substituting sulfuric acid with methanesulfonic acid as the supporting electrolyte for V and Ce in conjunction with a highly permselective polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) triblock copolymer AEM2 enabled a >95% reduction in capacity fade compared to previous sulfuric acid systems. Employing the Marcus-Hush kinetic formulation to understand the solvation effects3 4, the presence of strongly solvated cations was shown to be the reason for the significantly improved performance. The ED-RFB maintained nearly 100% coulombic efficiency (CE) and ca. 70% energy efficiency (EE) (at a 50 mA.cm-2 galvanostatic charge/discharge current) over 100 cycles. Thus, we demonstrate that judicious selection of the electrolyte composition leads to ED-RFBs with long life, excellent rate capability and stability.

Temperature-Dependent Order-to-Order Transition of Polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene Triblock Copolymer under Multilayered Confinement

The order-to-order transition (OOT) plays a key role in the nanotechnological applications of block copolymer (BCP) and is dramatically dependent on the spatial environment. A multilayer-confined space has been fabricated by layer-multiplying coextrusion technology to investigate the OOT mechanism of polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymer (SEBS) under multilayered confinement. The parallel oriented ordering front, whose OOT temperature is lower than that of the bulk due to higher free energy, is induced by the “substrate surface effect” in the SEBS layers of the multilayer specimens. The OOT temperature of SEBS is mainly decided by the volume fraction of ordering front. The propagation distance maximum of the “substrate surface effect” is about 220 nm. Only when the thickness of SEBS layer is less than this critical value is the whole SEBS layer fully filled with the ordering front. As a result, the OOT temperature first decreases rapidly and then tends to be a c...

Characterization of the surface morphology and grain growth near the surface of a block copolymer thin film with cylindrical microdomains oriented perpendicular to the surface

The grain size was evaluated by atomic force microscope observation for the thin film specimen of the polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymer in which the perpendicularly oriented polystyrene cylinders are existing, while that in the interior of the specimen was evaluated by the small-angle X-ray scattering measurements. Both results for the grain growth on the surface and in the interior of the sample exhibited power-law behavior with the same extent of the exponent (~0.45).

Time-resolved 2d-SAXS measurements to reveal mechanism of cylinder orientation upon sphere-to-cylinder transition under a planar flow in an SEBS triblock copolymer sheet

We report experimental results of time-resolved 2d-SAXS measurements for a polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS) triblock copolymer as-cast film, which was subjected to a planar flow gradually imposed in the heating process of the specimen at a ramp-up rate of 2°C/min. Before heating, non-equilibrium spheres were formed in the specimen. At 144°C, the spheres were found to completely transform into cylinders. Some extent of cylinder orientation (0.5 in orientation factor) was already achieved, even at that temperature the strain of the specimen was as low as 0.5. From this fact, the directional coalescence of non-equilibrium spheres along with the planar flow direction (FD) was implied. As temperature increased, it was found the progress of the cylinder orientation parallel to FD as well as the orientation of the (101¯0) planes of hexagonal lattice parallel to the substrate surface. The fraction of the peak-top intensities of the (112¯0) reflections, I(112¯0)/(I(101¯0)+I(112¯0)), was evaluated to examine the change in the orientational state of hexagonal lattice during application of the planar flow. The fraction was found to moderately increase with strain. However, the fraction of the grains, in which the (101¯0) planes are parallel to the specimen surface, is as low as 0.07 even at the highest strain state.

Complete and comprehensive orientation of cylindrical microdomains in a block copolymer sheet

Significant progress in cylindrical microdomain orientation is reported for a polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymer (SEBS-16) as analyzed by two-dimensional small-angle X-ray scattering. For this purpose, the morphological transition from sphere to cylinder was utilized. By applying compressional flow to the SEBS-16 specimen undergoing a morphological transition at 210 °C, superior cylinder orientation was achieved compared with the results obtained by applying the compressional flow to a cylindrical phase. The flow-treated specimens were further subjected to subsequent thermal annealing at 210 °C. It was found that the cylinder orientation proceeded by the subsequent thermal annealing even for flow-treated specimens with less oriented cylinders. Furthermore, the fraction of grains in which the plane of the hexagonal lattice of cylinders is oriented parallel to the specimen surface increased due to the subsequent thermal annealing, even for the specimen with the best cylinder orientation. Significant progress in cylindrical microdomain orientation is reported for a polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene triblock copolymer (SEBS-16) as analyzed by two-dimensional small-angle X-ray scattering. To achieve this goal, the morphological transition from sphere to cylinder was utilized. By applying compressional flow to the SEBS-16 specimen undergoing a morphological transition at 210 °C, superior cylinder orientation was achieved compared with the results obtained by applying compressional flow to the SEBS-16 specimen containing the cylindrical phase.

Polymer-Templated Carbon Hybridized Nanostructured Transition Metal Oxide As Advanced Lithium-Ion Anodes

An enormous spectrum of applications of lithium-ion batteries (LIBs), particularly in electric vehicles (EVs), hybrid EVs and electric grids, invokes essential requirements on their energy storage capabilities. However, the most common commercial graphite anode material still exhibits a relatively low theoretical specific capacity of 372 mAh g-1, which cannot meet the demand of the high-energy applications noted above. To date, a wide variety of anode materials with much higher capacities have been extensively investigated. In this regard, transition metal oxides (MxOy, where M is Fe, Co, Ni, Cu, Sn, Mn, etc.) clearly stand out as the promising alternatives to graphite owing to their attractive higher theoretical capacities (＞ 600 mAh g-1), low cost, environmental friendliness and wide availability containing earth-abundant elements. To further achieve high rate capability, hybrid nanomaterials with more conductive carbonaceous materials have been constructured. The ability to create a synergistic effect of nanostructure engineering and its hybridization with conductive carbonaceous material is highly desirable for attaining high-performance lithium ion batteries (LIBs). However, it remains challenging to achieve this synergy. Here we propose a general method to create a synergistic effect of nanostructure engineering and its hybridization with conductive carbonaceous material. Star-like and bottlebrush-like poly (acrylic acid)-block-polystyrene (PAA-PS) diblock copolymer and polystyrene-block-poly(acrylic acid)-block-polystyrene (PS-PAA-PS) triblock copolymer with controlled dimensions will be synthesized through atom transfer rapid polymerization (ATRP). Through a strong coordination bonding between the metal moiety of inorganic precursors and the functional groups of PAA (-COOH), the inorganic precursors can be selectively incorporated into the space formed by the PAA block. As a result, nanostructured transition metal oxide solid nanocrystals and hollow nanocrystals can be synthesized guided by the PAA-PS and PS-PAA-PS templates, respectively. In addition, by changing the polymeric templates from star-like to bottlebrush-like structure, the transition metal oxide nanocrystals varied from isotropic (i.e. nanoparticles, hollow nanoparticles) to anisotropic (i.e. nanorods, nanotubes). The diameter of the transition metal oxide nanocrystals is determined by the dimension of the PAA part, and it could be easily changed by varying the molecular weight of PAA part in the polymeric templates. Morever, the polymeric template not only serves as an easy control over the size and shape of the inorganic nanocrystals, but also acts as carbon source when calcinated at high temperature at argon atmosphere. We demonstrated that the carbon-hybridized nanocrystals obtained by the polymer templating method would be superior anode materials for LIBs.

Formation of nanophases in epoxy thermosets containing ABC and ACB triblock copolymers: A comparative investigation

Poly(ε-caprolactone)-block-polystyrene-block-poly(2,2,2-trifluoroethylacrylate (PCL-b-PS-b-PTFEA) and poly(ε-caprolactone)-block-poly(2,2,2-trifluoroethyl acrylate)-block-polystyrene (PCL-b-PTFEA-b-PS) triblock copolymers were synthesized via the combination of ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerizations. Both of the triblock copolymers had the similar composition and molecular weights but different sequential structures. These two triblock copolymers were utilized to modulate the nanostructures of epoxy thermosets. It was found that the microdomains in the thermosets were formed through the mechanism of reaction-induced demixing of PS blocks in the presence of the self-assembled PTFEA microdomains. In the thermosets containing PCL-b-PS-b-PTFEA, the spherical and cylindrical microdomains with the core-shell structure were formed. In those containing PCL-b-PTFEA-b-PS, the spherical microdomains were formed but the size of the microdomains displayed a bimodal distribution. The difference in morphology is accounted for by the influence of sequential structures of the copolymers on the reaction-induced demixing behavior of the triblock copolymers in the epoxy thermosets.

Polystyrene-block-poly (methoxy diethylene glycol acrylate)-block-polystyrene triblock copolymers in aqueous solution—a SANS study of the temperature-induced switching behavior

A concentrated solution of a symmetric triblock copolymer with a thermoresponsive poly(methoxy diethylene glycol acrylate) (PMDEGA) middle block and short hydrophobic, fully deuterated polystyrene end blocks is investigated in D2O where it undergoes a lower critical solution temperature-type phase transition at ca. 36 °C. Small-angle neutron scattering (SANS) in a wide temperature range (15–50 °C) is used to characterize the size and inner structure of the micelles as well as the correlation between the micelles and the formation of aggregates by the micelles above the cloud point (CP). A model featuring spherical core-shell micelles, which are correlated by a hard-sphere potential or a sticky hard-sphere potential together with a Guinier form factor describing aggregates formed by the micelles above the CP, fits the SANS curves well in the entire temperature range. The thickness of the thermoresponsive micellar PMDEGA shell as well as the hard-sphere radius increase slightly already below the cloud point. Whereas the thickness of the thermoresponsive micellar shell hardly shrinks when heating through the CP and up to 50 °C, the hard-sphere radius decreases within 3.5 K at the CP. The volume fraction decreases already significantly below the CP, which may be at the origin of the previously observed gel–sol transition far below the CP (Miasnikova et al., Langmuir 28: 4479–4490, 2012). Above the CP, small, and at higher temperatures, large aggregates are formed by the micelles.

Facile synthesis of block copolymers from a cinnamate derivative by combination of AGET ATRP and click chemistry

An azido- and bromo-containing compound derived from naturally occurring ethyl cinnamate was used successfully to prepare block copolymers by a combination of ‘activator generated by electron transfer atom transfer radical polymerization’ (AGET ATRP) and Huisgen “click” reactions in emulsion. First, azido-end poly(methyl methacrylate) and alkyne-end polystyrene were prepared under AGET ATRP conditions, then, poly(methyl methacrylate) block polystyrene (PMMA-b-PS) diblock copolymer was formed by Huisgen 1,3-dipolar cycloaddition. Finally, polystyrene block poly(methyl methacrylate) block polystyrene (PS-b-PMMA-b-PS) triblock copolymer was synthesized via simultaneous AGET ATRP and click reactions, catalyzed by the same copper-based catalyst. The polymers were characterized by 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC), which confirmed the successful synthesis of the corresponding polymers.

Gas-permeable composite hollow-fiber membrane with a three-layered structure

Gas-permeable composite hollow-fiber membrane with a three-layered structure composed of a high-density polyethylene (HDPE) porous layer, a MK-2F thin dense layer, and a HDPE porous layer has been successfully developed by melt-spinning and cold/hot stretching. The MK-2F thin dense layer was composed of a poly(ethylenebutylene)-block–polystyrene triblock copolymer (SEBS) phase and a (poly(ethylene-co-ethylacrylate) (EEA)+poly(ethylene-co-propylene) (EPP)) phase. When the stretching ratio was increased, oxygen permeance, fO2, and nitrogen permeance, fN2, were linearly increased, while the fO2/fN2 was almost constant at 2.95–3.0. The thickness of a no-pinhole thin layer was 2–5μm and its fO2 was 4.0–8.5×10−6cm3 (25°C)cm−2s−1cmHg−1. Structural analysis of the thin layer indicated that the SEBS and the (EEA+EPP) formed a 3D-network structure, which restricted elastic recovery of the SEBS matrix and led to the thin thickness. In a pervaporation experiment, the H2O vapor permeation rate of the MK-2F thin layer was about 1/4 that of polydimethyl silicone (PDMS), and the IPA vapor permeation rate was about 1/12 that of PDMS even though the gas permeance of the MK-2F thin layer was almost the same as that of PDMS.

Lamellar Morphology in Block Copolymers of Polystyrene and Poly[methyl(3,3,3-trifluoropropyl)siloxane

Well-defined polystyrene-block-poly[methyl(3,3,3-trifluoropropyl)siloxane] (PS-b-PMTFPS) diblock copolymers and polystyrene-block-poly[methyl(3,3,3-trifluoropropyl)siloxane]-block-polystyrene (PS-b-PMTFPS-b-PS) triblock copolymers with the volume fraction of PS between 0.46–0.61 were synthesized by anionic polymerization. The phase behavior and morphologies of the block copolymers were investigated via differential scanning calorimetry (DSC), rheological measurements, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Equilibrium domain orientations of well-ordered lamellar microphase-separated structures were observed in the PS-b-PMTFPS diblock and PS-b-PMTFPS-b-PS triblock copolymer melts. The results showed that the synthesized block copolymers were desirable for achieving long-range order resulting from a high driving force between PS and PMTFPS blocks.

Synthesis of antibacterial amphiphilic elastomer based on polystyrene-block-polyisoprene-block-polystyrene via thiol-ene addition

A new type of amphiphilic antibacterial elastomer has been described. Thermoplastic elastomer, polystyrene–block-polyisoprene–block-polystyrene (PS–b-PI–b-PS) triblock copolymer was functionalized in toluene solution by free radical mercaptan addition in order to obtain an amphiphilic antibacterial elastomer. Thiol terminated PEG was grafted through the double bonds of PS–b-PI–b-PS via free radical thiol-ene coupling reaction. The antibacterial properties of the amphiphilic graft copolymers were observed. The original and the modified polymers were used to create microfibers in an electro-spinning process. Topology of the electrospun micro/nanofibers were studied by using scanning electron microscopy (SEM). The chemical structures of the amphiphilic comb type graft copolymers were elucidated by the combination of elemental analysis, 1H NMR, 13C NMR, GPC and FTIR.

Deformation mechanisms in lamellar S–S/B–S triblock copolymers

The deformation behaviour of two lamellar polystyrene-block-poly(styrene-co-butadiene)-block-polystyrene (S–S/B–S) triblock copolymers was investigated by small-angle X-ray scattering (2D-SAXS) during uniaxial stretching. The samples differed by the styrene content in the statistical S/B middle block, being 50 and 70wt.% for LN50 and LN70 respectively. The positions of the SAXS reflections were estimated in order to relate the microscopic deformation behaviour with the macroscopic strain. The samples show different deformation mechanisms. A four-point SAXS pattern was found in LN50, which is typical for lamellae undulation and tilting. At higher strains, the contribution of lamellae tilting is decreasing until it is negligible at strains above 200%. During strain hardening, the deformation was affine, indicating triaxial deformation of the domains. In contrast, LN70 shows affine deformation in the whole investigated range. Thus, triaxial deformation is expected to dominate in LN70. The remarkable differences of the deformation mechanisms are expected to result from the different styrene contents in the S/B middle block. This leads to (i) a lower stiffness contrasts between the soft and hard phase and (ii) a reduced long-range order of the lamellae. Both factors may hinder lamellae tilting in LN70, which results in the absence of the four-point SAXS-pattern.

Size-controllable nanospheres prepared by blending a thermoset monomer in confined morphology with thermoplastic elastomer

Bisphenol-A based benzoxazine monomer (BZ) forms a polybenzoxazine (polyBZ) thermoset after thermal curing. However, when BZ is blended with polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene triblock copolymer (SEBS) matrices and is allowed to polymerize, phase separation at the nanometer level confines BZ in a way that can be controlled by the blending process, resulting in nanospherical polyBZ (polyBZ-NS) in the SEBS matrix. By simply changing the morphology of BZ and SEBS, through blending protocols ranging from sheet to electrospun micro-fibers and to electrospun core-sheath nanofibers, the sizes of polyBZ-NS so obtained vary from∼150–500 nm, to ∼80 nm, and to as low as ∼12 nm, respectively. This shows a new method to obtain well-defined mono-disperse nanospherical thermoset resins with a controllable size by controlling blend conditions.

Influence of Morphology on Mechanical Properties under the Combined Use of SEBS and EOr as Elastomer in PP/Elastomer/Filler Ternary Composites

The influences of combined elastomers on impact properties and morphology of polypropylene (PP)/elastomer/CaCO3 ternary composites were investigated. In the case that polystyrene- block-poly(ethylene-butene)- block-polystyrene triblock copolymer (SEBS) and poly(ethylene- co-octene) (EOR) were used as elastomers, a sea-island structure consisting of EOR dispersed phase and SEBS continuous phase was formed. The elastomer and the CaCO3 particles were separately dispersed in PP matrix. In the case that carboxylated SEBS (C-SEBS) and EOR were used, the C-SEBS particles were dispersed in the EOR particles. Almost all of the CaCO3 particles were dispersed in the PP matrix, although some of the CaCO3 particles were dispersed in the C-SEBS/EOR combined particles. Impact strength improved with an increase of incorporated CaCO3 particles. The effect of elastomer on the impact strength was SEBS ≥ SEBS/EOR > EOR = C-SEBS/EOR > C-SEBS. The morphology formed by elastomer and CaCO3 particles strongly affected the impact properties of the ternary composites.

Morphological Transition from Spherical to Lamellar Nanophases in Epoxy Thermosets Containing Poly(ethylene oxide)-block-poly(ε-caprolactone)-block-polystyrene Triblock Copolymer by Hardeners

In this study, we synthesized poly(ethylene oxide)-block-poly(e-caprolactone)-block-polystyrene (PEO-b-PCL-b-PS) triblock copolymer via the combination of ring-opening polymerization (ROP) and atom...

Influence of Filler Size on Impact Properties of PP/Elastomer/Filler Ternary Composites

Influence of filler size on impact properties for polypropylene (PP)/elastomer/filler ternary composites was investigated. Calcium carbonate (CaCO3) particles with a diameter in the range from 120 to 1200 nm were used as a filler and polystyrene-block-poly(ethylene-butene)-block-polystyrene triblock copolymer (SEBS) was used as an elastomer. In the PP/SEBS/CaCO3 ternary composite, CaCO3 particles and SEBS particles were dispersed in the PP matrix separately. In the case that SEBS elastomer volume fraction was below 0.12, the impact strength improved gradually with a decrease of CaCO3 mean diameter from 1200 to 160 nm. In the case that SEBS volume fraction was above 0.17, the impact strength improved significantly by the incorporation of CaCO3 particles with a mean diameter in the range from 120 to 900 nm. However, the impact strength hardly improved by the incorporation of CaCO3 particles with a mean diameter of 1200 nm.

Influences of Morphology on Mechanical Properties of Polypropylene/Elastomer/CaCO3 Ternary Composites

Relation between impact and mechanical properties and morphology of polypropylene (PP)/elastomer/filler ternary composite was investigated. Polystyrene-block-poly(ethylene-butene)-block-polystyrene triblock copolymer (SEBS) or carboxylated SEBS (C-SEBS) was used as elastomer and calcium carbonate (CaCO3) having mean size about 160 nm was used. In the PP/SEBS/CaCO3 ternary composite, CaCO3 particles and SEBS particles were dispersed in the PP matrix separately. In the PP/C-SEBS/CaCO3 ternary composites, CaCO3particles were embedded in C-SEBS, namely the core–shell particles were formed at lower CaCO3 concentration. However, some CaCO3 particles were dispersed directly in PP matrix at higher CaCO3 concentration. In order to clarify the influence of morphology, the measured modulus and tensile yield stress were compared with the predicted values by some prediction laws. In the PP/SEBS/CaCO3 composite, the impact strength increased with the amount of incorporated CaCO3 particles. Whereas, in the PP/C-SEBS/CaCO3 composite, the impact strength increased dependent on the amount of CaCO3 particles dispersed directly in PP matrix. From the observation of fractured surface, it was found that the impact strength is strongly affected by the morphology and dispersibility of CaCO3 particles.

Existence of microdomain orientation in thermoplastic elastomer through a case study of SEBS electrospun fibers

Although the microdomains of polymeric systems including the thermoplastic elastomers in the as-spun electrospun fiber were reported, the orientation of microdomains has not yet been well clarified. The present work shows an existence of microdomain orientation through a case study of a well-aligned electrospun fibers of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene triblock copolymer (SEBS) obtained from an electrospinning unit equipped with a rotational disk fiber-collector. Two-dimensional small-angle X-ray scattering (2D-SAXS) patterns of the as-spun electrospining SEBS fibers show elliptical and four-point patterns suggesting an orientation of distorted and fragmented lamellar microdomains. The electrospun fibers obtained from a low rotational disk collector speed (31.5 m/min) exhibits a significant microdomain distortion whereas the fibers obtained from high take-up velocities (310 m/min, 620 m/min, and 1240 m/min) show higher fragmented-microdomain stretching. By annealing the electrospun fibers, the fibers develop an isotropic SAXS pattern with traces of the remained anisotropic orientation. Based on the above mentioned evidences in SEBS, the present work, for the first time, clarifies that the as-spun thermoplastic elastomers fibers show not just a simple microdomain as used to be observed by transmission electron microscope (TEM) but rather with orientation which can be confirmed by SAXS.