Polystyrene Triblock Copolymer Research Articles

Exploiting the lower disorder-to-order temperature in polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers to increase their flow resistance at high temperature

This work focuses on the temperature-dependent structural and rheological characterization of polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers (PS-b-PnBA-b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the PnBA block as a major component, were synthesized. Small-angle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a PnBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and PnBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures.

Selective Plasticization of Poly (ethylene oxide) (PEO) Block in Nanostructured Polystyrene− PEO− Polystyrene Triblock Copolymer Electrolytes

The plasticization of a polymer electrolyte usually promotes its ionic conductivity but decreases its storage modulus due to the increased polymer chain flexibility. Herein, we show that such a tradeoff between the ionic conductivity and the mechanical robustness of the polymer electrolyte can be alleviated by selective plasticization of the ion-conductive block, such as poly(ethylene oxide) (PEO) in a polystyrene (PS)− PEO−PS block copolymer (SEO) electrolyte using an ether type plasticizer, tetraethylene glycol dimethyl ether (TEGDME). At maximum plasticizer loading, the room temperature ionic conductivity increases by up to 3 orders, whereas the storage modulus, G′ reduces to half, is still on the order of 102 MPa. At above the melting temperature of the PEO block, the dynamic storage modulus, G′ of the plasticized membrane surpasses its dry PS-PEO-PS counterpart. Such a phenomenon results from that, a) TEGDME co-crystallizes with PEO to promote its crystallinity and hence the storage modulus, b) TEGDME swells the amorphous PEO phase to enhance the polymer chain segmental mobility and hence ionic conductivity, and c) the PS phase remains intact from TEGDME to keep the SEO elastic.

Polymer Nanosheet Interfaced Bioelectrode for Skin‐Inert sEMG Measurement

AbstractThe interface between skin and electrodes plays a major role in the accuracy and efficiency of biopotential measurements. For reliable biosignal recording, stable and low‐impedance contact is required between electrodes and the target tissue. Conventional wet electrodes (Ag/AgCl) are composed of metal electrodes with skin‐adhesive hydrogel. However, for long‐term measurement, direct contact between the pre‐gel electrode and skin causes discomfort and skin irritation, especially for infants and people with sensitive skin because of the adhesiveness of the hydrogel. In this study, a low‐adhesive electrode is reported by exploiting a free‐standing polymeric ultra‐thin film (referred to as a “nanosheet”) as an intermediate layer at the backside of the electrode, which reduces the adhesiveness of the pre‐gel electrode while allowing for surface electromyogram (sEMG) measurement. Intermediate layer of the nanosheet made from polystyrene–polybutadiene–polystyrene triblock copolymer (SBS), polystyrene (PS) or polydimethylsiloxane (PDMS) is prepared using the roll‐to‐roll gravure coating method. The thickness of each nanosheet is varied from hundreds to thousands of nanometers, and the effect on the electrode performance is evaluated. The nanosheet‐modified electrodes with low adhesiveness are applied to human skin, which shows a good performance to detect sEMG signals of the forearm in a skin‐friendly manner.

Thermosensitive self-assembled behavior of poly (acrylamide-co-acrylonitrile)/polystyrene triblock copolymer and application in drug loading

Type poly(acrylamide-co-acrylonitrile) (P(AAm/AN)) is a typical thermosensitive polymer. It has a low solubility for some containing phenyl medicines. Introduction of segments with high affinity to medicines containing phenyl is helpful to improve the solubility for drugs. With the introduction of hydrophobic monomer units styrene, ABA type triblock polymer P(AAm/AN)-b-PS-b-P(AAm/AN) showed thermosensitive self-assembly behavior in aqueous solution. With the increasing of temperature, the triblock polymer experiences a process from to insoluble to from self-assembled structure and finally soluble. Accordingly, drug can be encapsulated, partly released, and completely released. This triblock polymer has the potential application in load drug release.

The Impact of Selectively Plasticized Poly (ethylene oxide) (PEO) Block in Nanostructured Polystyrene−PEO−Polystyrene Triblock Copolymer Electrolytes

All polymer electrolytes, including block polymer (BP) electrolytes exhibit low ionic conductivity compared to liquid electrolytes. For homopolymer electrolytes, the ionic conductivity can be increased by incorporating plasticizer into the polymer network. However, the subsequent weakened mechanical structure of the network precludes its use in many practical applications. In this work, we selectively plasticize the PEO block in a polystyrene PS-PEO-PS triblock copolymer electrolyte using a PEO-like plasticizer: tetraethylene glycol dimethyl ether (TEGDME). Unlike its homopolymer (PEO) electrolyte counterpart, the mechanical properties of the PS-PEO-PS triblock copolymer electrolyte are not drastically degraded by this plasticizer because it is immiscible in the nonpolar PS block domains. Polymer electrolyte membranes were cast from lithium trifluoromethanesulfonate (LiTFS) solutions with the corresponding polymers. The molar ratio of ethylene oxide to Li+ is 16 for all electrolytes (nEO:nLi = 16:1). The ionic conductivity of the PS-PEO-PS electrolyte at 80 °C is about one order of magnitude lower than that of the homopolymer (PEO) counterpart at the same temperature. However, the shear modulus (G’) of the PS-PEO-PS electrolyte is about three orders of magnitude higher than the homopolymer, indicating the mechanical properties of the copolymer electrolyte is primarily dominated by the PS phase. The addition of TEGDME plasticizer to the PEO homopolymer electrolyte resulted in a ~10% increase in conductivity. The addition of same amount of TEGDME to the PS-PEO-PS electrolyte resulted in ~100% increase in conductivity. Compared to the dry electrolyte counterpart, the low isothermal frequency (ω = 0.1 rad/s) elastic modulus, G’ of the TEGDME plastized PS-PEO-PS was reduced to half at 80 °C (on the order of 106 Pa). Surprisingly, G’ of the plastized membrane surpassed its dry PS-PEO-PS counterpart at higher frequency values (17 < ω < 100 rad/s). This counter intuitive result is further explored using: 1) Fourier-transform infrared spectroscopy (FTIR) to elucidate the salt solvation and coordination to ether oxygens, and 2) small angle X-ray scattering (SAXS) to decipher the domain spacing of the adjacent copolymer blocks. Acknowledgment This work is supported by Dr. Imre Gyuk, Manager, Energy Storage Program, Office of Electricity Delivery and Reliability, Department of Energy. CC acknowldge partial financial support by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

Synthesis and interface stability of polystyrene-poly(ethylene glycol)-polystyrene triblock copolymer as solid-state electrolyte for lithium-metal batteries

The development of safe and long-term stable solid polymer electrolytes is a major challenge for all solid-state batteries because good interfacial stability toward electrodes is the main concern. In this paper, a triblock copolymer polystyrene-poly(ethylene glycol)-polystyrene (PS-PEG-PS) is synthesized and investigated as solid polymer electrolyte. This polymer electrolyte exhibits a high ionic conductivity of 1.1 × 10−3 S cm −1 at 70 °C, transference number of 0.17, high degree flexibility, good mechanical strength and thermal stability. The interface stability of the solid-polymer electrolyte is investigated in Li metal cell and the comprehensive electrochemical properties are studied in cells with either LiFePO4 or LiNi0.5Co0.3Mn0.2O2 cathode materials. Good rate capability and excellent cyclability of the solid polymer electrolyte is demonstrated, with an electrochemical stability window extending above 4.5 V vs. Li+/Li. Furthermore, constant voltage impedance measurements give evidence of the better interface stability and rate capability of LiNi0.5Co0.3Mn0.2O2//Li battery. Meanwhile, molecular orbital energy levels calculated by density functional theory are consistent with experiments.

Synthesis of Block Copolymers of Polyester and Polystyrene by Means of Cross-Metathesis of Cyclic Unsaturated Polyester and Atom Transfer Radical Polymerization

Synthesis of B–A–B type triblock copolymers of aliphatic polyester (PEs) and polystyrene (PSt) was investigated by using cyclic unsaturated PEs prepared by conventional polycondensation of 4-octene-1,8-diol and sebacoyl chloride. The obtained cyclic PEs underwent cross-metathesis with PSt containing a carbon–carbon double bond (C═C) at the central position, which was obtained by atom transfer radical polymerization (ATRP) of styrene with a bifunctional initiator containing a C═C bond. PSt with a longer methylene spacer between the C═C bond and PSt successfully afforded the PSt-b-PEs-b-PSt triblock copolymer. As another approach to obtain the triblock copolymer, cross-metathesis of cyclic PEs with 2-butene-1,4-diol or 4-octene-1,8-diol bis(2-bromoisobutyrylate)s was conducted to afford linear PEs having ATRP initiation sites at both ends, followed by ATRP of styrene. The unsaturated PEs segment in the triblock copolymer obtained by the second approach was converted into a saturated PEs segment by treatment...

In Situ Cross-Linked Gel Polymer Electrolyte Membranes with Excellent Thermal Stability for Lithium Ion Batteries.

Novel gel polymer electrolyte membranes with excellent thermal stability are fabricated via a combination of physical blending and chemical cross-linking procedures. Precursor porous membranes made of poly(vinylidene fluoride) (PVDF) and polystyrene–poly(ethylene oxide)–polystyrene (PS–PEO–PS) triblock copolymer composites are prepared by a phase-inversion technique, and the gel polymer electrolyte membranes are finished by in situ hypercrosslinking of the PS segments in precursor membranes. The latter cross-linking procedure could consolidate pore configuration and thus greatly enhance the thermal stability of the obtained cross-linked composite membranes. The membranes with optimal PS/PEO ratios can retain reasonable porosity with little dimensional shrinkage at high temperatures up to 260 °C. Gel polymer electrolytes with these cross-linked membranes as matrices exhibit much higher ionic conductivities (up to 1.38 × 10–3 S cm–1 at room temperature) than those based on pure PVDF membranes. Li/LiFePO4 half cells assembled with these gel polymer electrolytes exhibit good cycling performance and rate capability. These results indicate that the Friedel–Crafts reaction based hypercrosslinking is an efficient method to construct highly heat-resistant polymer electrolytes for lithium ion batteries, particularly advantageous in applications that require high-temperature usage.

Evolution of Microstructure in Block Copolymer Thin Films during Zone Annealing

The effect of zone annealing on a microstructure from horizontal and vertical cylinders in the microphase-separated films of polystyrene–polybutadiene–polystyrene triblock copolymer and polystyrene–poly(4-vinylpyridine) diblock copolymer is studied. It is shown that processing of the films of different thicknesses at various maximum thermal front temperatures which do not exceed the temperature of orderdisorder transition does not lead to a noticeable increase in their degree of ordering. On the contrary, once the transition temperature is approached, the interfacial area between domains formed by different types of blocks is increased and the order in their arrangement disappears, with the thermal stability of the structure falling with an increase in film thickness. Thus, the substantial microstructure ordering during the cold zone annealing of the polystyrene–poly(methyl methacrylate) diblock copolymer described in the literature has not yet been reproduced for other systems. The maximum rate of gradient zone motion at which this effect is to be expected is estimated.

MEMS optical interferometry-based pressure sensor using elastomer nanosheet developed by dry transfer technique

We developed an elastomer-based Fabry–Perot interferometer with a submicron gap between a freestanding thin film and a substrate by a dry transfer technique. A newly developed elastomeric nanosheet using a polystyrene–polybutadiene–polystyrene triblock copolymer (SBS) provides a low Young’s modulus of 40 MPa, a large elastic strain of 38%, and high adhesiveness. A freestanding SBS nanosheet can be formed by a dry transfer technique without vacuum and high-temperature processes owing to the high adhesiveness of SBS nanosheets. With the pressure change, the freestanding nanosheet was found to deform with good adhesion between the dry transferred SBS and the substrate.

Polystyrene Chain Growth from Di-End-Functional Polyolefins for Polystyrene-Polyolefin-Polystyrene Block Copolymers.

Triblock copolymers of polystyrene (PS) and a polyolefin (PO), e.g., PS-block-poly(ethylene-co-1-butene)-block-PS (SEBS), are attractive materials for use as thermoplastic elastomers and are produced commercially by a two-step process that involves the costly hydrogenation of PS-block-polybutadiene-block-PS. We herein report a one-pot strategy for attaching PS chains to both ends of PO chains to construct PS-block-PO-block-PS directly from olefin and styrene monomers. Dialkylzinc compound containing styrene moieties ((CH2=CHC6H4CH2CH2)2Zn) was prepared, from which poly(ethylene-co-propylene) chains were grown via “coordinative chain transfer polymerization” using the pyridylaminohafnium catalyst to afford di-end functional PO chains functionalized with styrene and Zn moieties. Subsequently, PS chains were attached at both ends of the PO chains by introduction of styrene monomers in addition to the anionic initiator Me3SiCH2Li·(pmdeta) (pmdeta = pentamethyldiethylenetriamine). We found that the fraction of the extracted PS homopolymer was low (~20%) and that molecular weights were evidently increased after the styrene polymerization (ΔMn = 27–54 kDa). Transmission electron microscopy showed spherical and wormlike PS domains measuring several tens of nm segregated within the PO matrix. Optimal tensile properties were observed for the sample containing a propylene mole fraction of 0.25 and a styrene content of 33%. Finally, in the cyclic tensile test, the prepared copolymers exhibited thermoplastic elastomeric properties with no breakage up over 10 cycles, which is comparable to the behavior of commercial-grade SEBS.

Molecular design and synthesis of acrylic resin film-forming materials with wide applicable temperature range via RAFT emulsion polymerization

Abstract The symmetric polystyrene- block -poly( n -butyl acrylate)- block -polystyrene (SAS) triblock copolymers with wide applicable temperature range have been designed and synthesized via reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. The high poly( n -butyl acrylate) (PBA) block content introduced will endow the SAS with the ability of working as film-forming materials. The microphase separation and mechanism of wide applicable temperature range were investigated by differential scanning calorimetry and dynamic mechanical analysis (DMA). The static and dynamic mechanical properties, visible light transmittance, water resistance and thermal stability of SAS were also characterized by tensile test, DMA, spectrophotometer, water absorption and thermogravimetric analysis. The tensile strength decreases and elongation at break increases with the PBA block content of SAS increasing from 50 wt.% to 70 wt.%. The maximum elongation at break reaches 707%. The broad thermoplastic elastic region from −40 °C to 80 °C works well in the surrounding of a big temperature difference due to the PBA block in rubbery state and the PSt block in glassy state. The SAS has high transmittance, low water absorption and favorable thermal stability. This research will provide a reference for film-forming materials with wide applicable temperature range.

Self‐Assembly‐Driven Electrospinning: The Transition from Fibers to Intact Beaded Morphologies

Polymer beads have attracted considerable interest for use in catalysis, drug delivery, and photonics due to their particular shape and surface morphology. Electrospinning, typically used for producing nanofibers, can also be used to fabricate polymer beads if the solution has a sufficiently low concentration. In this work, a novel approach for producing more uniform, intact beads is presented by electrospinning self-assembled block copolymer (BCP) solutions. This approach allows a relatively high polymer concentration to be used, yet with a low degree of entanglement between polymer chains due to microphase separation of the BCP in a selective solvent system. Herein, to demonstrate the technology, a well-studied polystyrene-poly(ethylene butylene)-polystyrene triblock copolymer is dissolved in a co-solvent system. The effect of solvent composition on the characteristics of the fibers and beads is intensively studied, and the mechanism of this fiber-to-bead is found to be dependent on microphase separation of the BCP.

Sub-10 nm Scale Nanostructures in Self-Organized Linear Di- and Triblock Copolymers and Miktoarm Star Copolymers Consisting of Maltoheptaose and Polystyrene

The present paper describes the sub-10 nm scale self-assembly of AB-type diblock, ABA-type triblock, and A2B-type miktoarm star copolymers consisting of maltoheptaose (MH: A block) and polystyrene (PS: B block). These block copolymers (BCPs) were synthesized through coupling of end-functionalized MH and PS moieties. Small-angle X-ray scattering and atomic force microscope investigations indicated self-organized cylindrical and lamellar structures in the BCP bulks and thin films with domain spacing (d) ranging from 7.65 to 10.6 nm depending on the volume fraction of MH block (ϕMH), Flory–Huggins interaction parameter (χ), and degree of polymerization (N). The BCP architecture also governed the morphology of the BCPs, e.g. the AB-type diblock copolymer (ϕMH = 0.42), the ABA-type triblock copolymer (ϕMH = 0.40), and the A2B-type miktoarm star copolymer (ϕMH = 0.45) self-organized into cylinder (d = 7.65 nm), lamellar (d = 8.41 nm), and lamellar (d = 9.21 nm) structures, respectively.

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.

Linear viscoelasticity of unentangled corona blocks and star arms

ABA-type triblock copolymers form micellar structures consisting of B-rich cores and A-rich coronas in A-selective solvents. The relaxation of A corona is known to be qualitatively similar to but quantitatively different from that of a star-shaped A chain due to the geometric (spatial) constraint by the core and the thermodynamic (osmotic) constraint. The effect of the geometric constraint on the block dynamics can be modeled by a chain with one end grafted onto an impenetrable wall. We show that the impenetrable wall slightly accelerates the end-to-end vector relaxation in a direction normal to the wall while it slightly decelerates the viscoelastic terminal relaxation. To test this prediction, we performed linear viscoelastic measurements for model systems: For polystyrene–polyisoprene–polystyrene (SIS) triblock copolymers in S-selective solvent (diethyl phthalate) forming micelles, the viscoelastic relaxation of unentangled S blocks (corona blocks) was indeed slower compared with that of star-branched S chains having the same molecular weight. Nevertheless, the deceleration was stronger than that expected from our theory, and possible reasons were discussed.

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.

Separation of Parent Homopolymers from Polystyrene-b-poly(ethylene oxide)-b-polystyrene Triblock Copolymers by Means of Liquid Chromatography: 1. Comparison of Different Methods

Separation of parent homopolymers, polystyrene and poly(ethylene oxide), from the triblock copolymer polystyrene-b-poly(ethylene oxide)-b-polystyrene was investigated by means of liquid chromatography techniques. Overall suitability was evaluated and compared for size exclusion chromatography, (SEC), liquid chromatography under critical conditions of enthalpic interactions (LC CC), and liquid chromatography under limiting conditions of desorption (LC LCD). Among these techniques, LC LCD was the only one able to fully separate block copolymers from both their parent homopolymers in one single run. The efficiency of the separation was proven by (1)H NMR analysis of previously collected fractions.

Influence of the epoxidation degree of a polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer on the compatibilization with an organomodified nanoclay

In this work, the addition of organophilic-modified montmorillonite into polystyrene–polybutadiene–polystyrene (SBS) triblock copolymers was investigated with and without the use of epoxidized SBS as a compatibilization agent. The nanocomposites were prepared by melting mixture at 60 rpm and 130 °C. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), tensile tests, and dynamic-mechanical analysis (DMA). XRD and TEM showed the formation of an intercalated dispersion of clay platelets oriented on the SBS surface. The AFM showed the typical lamellar microstructure of the styrene and butadiene phases of SBS. The estimation of the average distance between the styrene lamellae by AFM analysis showed that the platelets are anchored between the phases, and this structural feature caused an increase in elastic modulus. DMA analysis showed that the T g of butadiene decreased in the nanocomposites. The decrease of the T g and the increase in the elastic modulus are correlated to mechanisms at the micro- and the macro-scales, respectively. The decrease in the T g indicates flexibilization at the interface, whereas the intercalation of the platelets restricted the interphase macroscale deformation.

Separation and composition distribution determination of triblock copolymers by thermal field-flow fractionation

Thermal field-flow fractionation (ThFFF) is used to separate a linear triblock copolymer of polystyrene, poly(tert-butyl acrylate), and poly(methyl methacrylate) by composition. Fractions were collected and subjected to off-line NMR analysis. The resultant mole fraction versus retention time plots for each of the three polymer components confirmed the success of the separation and yielded the composition distribution of the copolymer. The composition distribution was also obtained using a second approach that involved solving a series of equations comprised of polymer thermal diffusion coefficients and quasi-elastic light scattering, differential refractometry, and UV detector responses. Both sets of data showed similar trends of composition variations in each polymer component as a function of retention time. However, discrepancies were observed in the mole fraction values. The ability to compositionally separate and to determine composition distribution of copolymers is important as demonstrated by the presence of diblock impurities in the ThFFF with off-line NMR results.