Triblock Copolymer Membranes Research Articles

Multiscale modeling of solute diffusion in triblock copolymer membranes.

We develop a multiscale simulation model for diffusion of solutes through porous triblock copolymer membranes. The approach combines two techniques: self-consistent field theory (SCFT) to predict the structure of the self-assembled, solvated membrane and on-lattice kinetic Monte Carlo (kMC) simulations to model diffusion of solutes. Solvation is simulated in SCFT by constraining the glassy membrane matrix while relaxing the brush-like membrane pore coating against the solvent. The kMC simulations capture the resulting solute spatial distribution and concentration-dependent local diffusivity in the polymer-coated pores; we parameterize the latter using particle-based simulations. We apply our approach to simulate solute diffusion through nonequilibrium morphologies of a model triblock copolymer, and we correlate diffusivity with structural descriptors of the morphologies. We also compare the model's predictions to alternative approaches based on simple lattice random walks and find our multiscale model to be more robust and systematic to parameterize. Our multiscale modeling approach is general and can be readily extended in the future to other chemistries, morphologies, and models for the local solute diffusivity and interactions with the membrane.

Triblock SEBS/DVB crosslinked and sulfonated membranes: Fuel cell performance and conductivity

AbstractA set of styrene‐ethylene‐butylene‐styrene triblock copolymer (SEBS) membranes with 10 or 25 wt% divinyl‐benzene (DVB) as a crosslinking agent were prepared and validated. Physicochemical characterization revealed suitable hydrolytic and thermal stability of photo‐crosslinked membranes containing 25 wt% DVB and post‐sulfonated. These compositions were evaluated in H2/O2 single cells, and electrical and proton conductivities were furtherly assessed. The membranes with the milder post‐sulfonation showed greater proton conductivity than those with excessive sulfonation. In terms of electrical conductivity, a universal power law was applied, and the values obtained were low enough for being used as polyelectrolytes. At the analyzed temperatures, the charge transport process follows a long‐range pathway or vehicular model. Finally, fuel cell performance revealed the best behavior for the membrane with 25 wt% DVB, photo‐crosslinked during 30 min and mild sulfonated, with a promising power density of 526 mW·cm−2. Overall, the results obtained highlight the promising fuel cell performance of these cost‐effective triblock copolymer‐based membranes and indicate that higher sulfonation does not necessarily imply better power density.

Gas-separation and physical properties of ABA triblock copolymers synthesized from polyimide and hydrophilic adamantane derivatives

In this study, ABA triblock copolymers derived from 4,4’-(hexafluoroisopropylidene)-diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TeMPD; PI) and 3-hydroxy-1-adamantyl methacrylate (HAdMA) or 3,5-dihydroxy-1-adamantyl methacrylate (DHAdMA) have been synthesized via atom transfer radical polymerization to generate mechanically tough and thermally stable gas-separation membranes with composition-tunable transport properties. Due to the inherent thermodynamic incompatibility between the chemically dissimilar blocks, these two series of triblock copolymers appear microphase-separated. While the gas permeability coefficients of these triblock copolymer membranes are consistently lower than that of PI due to the reduced fractional free volume of HAdMA and DHAdMA, the solubility coefficients of the copolymers are higher than that of PI due presumably to specific interactions between the polar hydroxyl group(s) and penetrant gas molecules. These triblock copolymers synthesized from PI and hydrophilic adamantane derivatives constitute a new class of nanostructured polymeric materials possessing excellent thermomechanical properties in conjunction with designer gas-separation properties.

Novel self-cross-linked multi-imidazolium cations long flexible side chains triblock copolymer anion exchange membrane based on ROMP-type polybenzonorbornadiene

A novel benzonorbornadiene derivative (BenzoNBD-Bis(Im+Br−-Im+I−)) grafted by multi-imidazolium cations side-chains combined the rigid alkyl spacer and flexible alkoxy spacer is designed and synthesized. Then, the BenzoNBD-Bis(Im+Br−-Im+I−) monomer is copolymerized with the epoxy functionalized norbornene monomer (NB-MGE) and norbornene (NB) via ring-opening metathesis polymerization (ROMP) using Grubbs 3rd catalyst. All as-designed triblock copolymer membranes (TBCMs) show a thermal decomposition temperature beyond 310 °C and can well be dissolved in common organic solvents. The self-cross-linked structure of anion exchange membrane (AEM) is confirmed by gel fraction and tensile measurement. The water uptake and swelling ratio of TBCMs and AEMs are also measured. Major properties required for AEMs such as ion exchange capacity (IEC), hydroxide conductivity and alkaline stability are investigated. AEM-9.09 shows a hydroxide conductivity of 100.74 mS cm−1 at 80 °C. Besides, the micro-phase separated morphology of AEM is confirmed by TEM, AFM and SAXS analyses, AEMs formed distinct micro-phase separation. The as-prepared AEM exhibits a peak power density of 174.5 mW cm−2 at 365.1 mA cm−2 tested in a H2/O2 single-cell anion exchange membrane fuel cell (AEMFC) at 60 °C. The newly developed strategy of self-cross-linked multi-imidazolium cations long side-chains triblock benzonorbornadiene copolymer provides an effective method to develop high-performance AEMs.

Connecting Solute Diffusion to Morphology in Triblock Copolymer Membranes

Block copolymers self-assemble into a variety of morphologies that can serve as templates for preparing conductive or porous materials such as batteries and membranes. These morphologies can be eit...

Influence of pore morphology on the diffusion of water in triblock copolymer membranes.

Understanding the transport properties of water in self-assembled block copolymer morphologies is important for furthering the use of such materials as water-purifying membranes. In this study, we used coarse-grained dissipative particle dynamics simulations to clarify the influence of pore morphology on the self-diffusion of water in linear-triblock-copolymer membranes. We considered representative lamellar, cylindrical, and gyroid morphologies and present results for both the global and local diffusivities of water in the pores. Our results suggest that the diffusivity of water in the confined, polymer-coated pores differs from that in the unconfined bulk. Explicitly, in confinement, the mobility of water is reduced by the hydrodynamic friction arising from the hydrophilic blocks coating the pore walls. We demonstrate that in lamella and cylindrical morphologies, the latter effects can be rendered as a universal function of the pore size relative to the brush height of the hydrophilic blocks.

The effect of poly(alkyl (meth)acrylate) segments on the thermodynamic properties, morphology and gas permeation properties of poly(alkyl (meth)acrylate)-b-poly(dimethyl siloxane) triblock copolymer membranes

The structure-property relationship of the poly(alkyl (meth)acrylate)-b-poly(dimethyl siloxane) (PA-b-PDMS) triblock copolymers were studied for membrane application. The effect of PA segments with different main-chain flexibility and side chains such as poly(benzyl methacrylate) (PBzMA), poly(ethyl methacrylate) (PEMA) and poly(methyl acrylate) (PMA) were studied on the properties of PA-b-PDMS block copolymer membranes. The block copolymers were synthesized via atom transfer radical polymerization (ATRP). The morphology structure of the synthesized block copolymers was changed from spherical to the cylindrical type by changing the structural segments from PMA and P(EMA-b-PEMA) to PEMA, respectively. The morphological feature of the PA-b-PDMS block copolymers was discussed according to their thermodynamic properties (surface energy, the solubility parameter of the constituent segments, and binary interaction parameters). The glass transition temperature of the hard segments of PA-b-PDMS block copolymers was increased by increasing poly(alkyl methacrylate) segments. CO2 permeability of the P(EMA-co-MA)-b-PDMS-b-P(EMA-co-MA) block copolymers was increased (from 7.2 Barrer to 908 Barrer) by increasing MA repeating units which correlated to the higher main chain flexibility of MA compared to the EMA repeating units. Permeability of CO2 was increased 27% by substitution of BzMA repeating units of P(BzMA-co-MA)-b-PDMS-b-P(BzMA-co-MA) block copolymer with EMA and correlated with the lower fractional free volume of BzMA repeating units.

Effect of salt concentration in spinning solution on fiber diameter and mechanical property of electrospun styrene-butadiene-styrene tri-block copolymer membrane

Electrospun nanofiber is regarded as a promising candidate for many high-end applications due to its advantageous unique structure. Ultrafine fiber and good mechanical property are essential to ensure its performance. In this work, tunable ultrafine diameter and significantly enhanced mechanical strength of electrospun Styrene-butadiene-styrene tri-block copolymer (SBS) membrane are attained by means of the addition of LiBr into SBS solution dissolved in tetrahydrofuran/dimethylformamide (THF/DMF). Solution conductivity is found to grow in two steps with the increasing lithium bromide (LiBr) concentration and a critical point is observed at the ultralow concentration of 0.005 wt%, sharp increase below it but modest increase above it. Interestingly, the diameter of electrospun fiber shows a significant reduction with increase of LiBr concentration below this critical point but minor fluctuation above this. Welded structure is observed between adjacent fibers and the degree of welding goes deeper with increase of salt concentration. Accordingly, the mechanical strength of electrospun membrane is gradually enhanced and reaches to the highest value of 5.7 MPa at the critical concentration, with enhancement of 134% in comparison with pure electrospun SBS membrane, and then declines when further adding LiBr. TEM observation confirms more oriented and distinct self-assembly domains in the finer fibers, which contribute greatly to the property enhancement for electrospun SBS membrane obtained below critical concentration. The finding of critical concentration is important for the preparation of high performance electrospun membrane by adding salt in the spinning solution.

Mid-block quaternized polystyrene-b-polybutadiene-b-polystyrene triblock copolymers as anion exchange membranes

A novel mid-block, side-chain-type quaternized triblock copolymer was prepared from commercial polystyrene-b-polybutadiene-b-polystyrene (SBS) triblock copolymers by Markovnikov addition reaction with HBr, azidation, and Cu(I)-catalyzed click reaction for high-performance anion exchange membranes (AEM). After the optimization of reaction conditions, the bromination, azidation and subsequently Cu(I)-catalyzed click reactions have been confirmed to be quantitative according to the NMR results. The anion-conductive, mid-block triblock copolymer (SBS-c-QA) membrane was obtained from casting its DMF solution. As a control experiment, the mid-block quaternized SBS (SBS-QA) membrane was also synthesized by direct quaternization of brominated SBS with trimethylamine. The SBS-c-QA membrane with pendent quaternary ammounium groups showed much lower water uptake than that of SBS-QA membrane. However, comparable bicarbonate conductivities of 5.6 mS/cm at 20 °C and 20.5 mS/cm at 80 °C were obtained for SBS-c-QA membrane in spite of its low ion exchange capacity (IEC) (1.10 meq./g) and low water uptake (18 wt%). Thus, the SBS-c-QA membrane displayed high IEC-normalized conductivity which can be attributed to the side-chain architecture of the triblock copolymer. The alkaline stability testing indicated that SBS-c-QA membrane showed a higher alkaline stability than SBS-QA membrane. A high retention of bicarbonate conductivity (70%) was observed after degradation testing in 1 M NaOH at 80 °C for 216 h. These results suggested that incorporating the side-chain-type QA cations into the mid-block of the triblock copolymer was an effective method to fabricate AEMs with both high ionic conductivity and excellent alkaline stability.

Anion Conductive Triblock Copolymer Membranes with Flexible Multication Side Chain

To achieve highly conductive and stable anion exchange membranes (AEMs) for fuel cells, novel triblock copolymer AEMs bearing flexible side chain were synthesized. The triblock structure and flexible side chain are responsible for the developed hydrophilic/hydrophobic phase separated morphology and well-connected ion conducting channels, as confirmed by transmission electron microscopy. As a result, the triblock copolymer AEMs with flexible side chain (ABA-TQA- x) demonstrated considerably higher conductivities, up to 130.5 mS cm-1 at 80 °C, than the AEMs with monocation side chain (ABA-MQA). Furthermore, the long alkyl spacer between the backbone and quaternary ammonium groups, as well as long intercation spacer limits the water swelling of the membranes to some degree, resulting in good alkaline stability. The ABA-TQA-44 membrane retained 84.7% and 83.1% of its original conductivity and ionic exchange capacity, respectively, after immersed in a 1 M aqueous KOH solution at 80 °C for 480 h. Furthermore, the peak power density of a H2/O2 single cell using ABA-TQA-44 is 204.6 mW cm-2 at a current density of 500 mA cm-2 at 80 °C.

Dynamics of bridge-loop transformation in a membrane with mixed monolayer/bilayer structures.

Instead of forming a typical bilayer or monolayer membrane, both the bridge (I-shape) and loop (U-shape) conformations coexist in the planar membranes formed by ABA triblock copolymers in a selective solvent. The non-equilibrium and equilibrium relaxation dynamics of polymer conformations are monitored. The non-equilibrium relaxation time depends on the initial composition and increases with an increase in the immiscibility between A and B blocks. The equilibrium composition of the loop-shape polymer is independent of the initial composition and A-B immiscibility. However, the extent of equilibrium composition fluctuations subsides as the A and B blocks become highly incompatible. The influences of the A-B immiscibility on the geometrical, mechanical, and transport properties of the membrane have also been investigated. As the immiscibility increases, the overall membrane thickness and the B block layer thickness (h) increase because of the increment in the molecular packing density. As a result, both the stretching (KA) and bending (KB) moduli grow significantly with the increasing A-B immiscibility. Consistent with the case of typical membranes, the ratio KB/KAh2 = 2 × 10-3 is a constant. Although the lateral diffusivity of polymers is insensitive to immiscibility, the membrane permeability decreases substantially as the A-B immiscibility is increased.

Tailoring Membrane Surface Properties and Ultrafiltration Performances via the Self-Assembly of Polyethylene Glycol-block-Polysulfone-block-Polyethylene Glycol Block Copolymer upon Thermal and Solvent Annealing.

Recently, ultrafiltration (UF) membranes have faced great challenges including the fine control of membrane surfaces for high filtration performances and antifouling properties in treating complex solution systems. Here, a particular type of amphiphilic block copolymer polyethylene glycol-block-polysulfone-block-polyethylene glycol (PEG-b-PSf-b-PEG) was synthesized through one-pot step-growth polymerization with mPEG [monomethylpoly(ethylene glycol)] as two ends to achieve the mobility of hydrophilic polymer chains. Without any other polymers or additives involved, the PEG-b-PSf-b-PEG triblock copolymer UF membrane was fabricated through the non-solvent-induced phase separation (NIPS) method. The surface properties and filtration performances of UF membranes were tailored through the self-assembly of PEG-b-PSf-b-PEG triblock copolymers combining the thermal and solvent annealing treatments in water at 90 °C for 16 h. The annealed PEG-b-PSf-b-PEG triblock copolymer membrane significantly enhanced its water flux resulting from the increased mean pore size with the improved porosity, as well as the decreased skin layer thickness, upon annealing. More importantly, the PEG-b-PSf-b-PEG triblock copolymer membrane surface turned from hydrophobic to hydrophilic upon annealing with the PEG enrichment on the surface, and exhibited improved protein antifouling performances. Our research opens a new avenue to tailor the membrane structure and surface properties by self-assembly of amphiphilic block copolymers upon thermal and solvent annealing treatments.

Functionalizing polyplex surface through self-assembly of a rationally designed tri-block copolymer membrane around the nucleic acid core for systemic delivery

Functionalizing polyplex surface through self-assembly of a rationally designed tri-block copolymer membrane around the nucleic acid core for systemic delivery

Improving proton conduction pathways in di- and triblock copolymer membranes: Branched versus linear side chains.

Phase separation within a series of polymer membranes in the presence of water is studied by dissipative particle dynamics. Each polymer contains hydrophobic A beads and hydrophilic C beads. Three parent architectures are constructed from a backbone composed of connected hydrophobic A beads to which short ([C]), long ([A3C]), or symmetrically branched A5[AC][AC] side chains spring off. Three di-block copolymer derivatives are constructed by covalently bonding an A30 block to each parent architecture. Also three tri-blocks with A15 blocks attached to both ends of each parent architecture are modeled. Monte Carlo tracer diffusion calculations through the water containing pores for 1226 morphologies reveal that water diffusion for parent architectures is slowest and diffusion through the di-blocks is fastest. Furthermore, diffusion increases with side chain length and is highest for branched side chains. This is explained by the increase of water pore size with 〈Nbond〉, which is the average number of bonds that A beads are separated from a nearest C bead. Optimization of 〈Nbond〉 within the amphiphilic parent architecture is expected to be essential in improving proton conduction in polymer electrolyte membranes.

Preparation and Performance of Poly(D,L-lactic acid)–Polyethylene Glycol–Poly(D,L-lactic acid) Electrospun Fibrous Membranes for Drug Release.

In this study, poly(D,L-lactic acid)–polyethylene glycol–poly(D,L-lactic acid), hereafter referred to as PDLLA–PEG–PDLLA, triblock copolymer membranes were prepared by electrospinning. Scanning electron microscopy images revealed the morphology of the microfibers, which had a diameter ranging from 300 to 900 nm. Fourier transform infrared spectroscopy was employed for structural analysis of the PDLLA–PEG–PDLLA/florfenicol (FF) membranes, which exhibited three absorption peaks at 3455, 1684, and 1533 cm−1, respectively, indicating that the triblock copolymer and FF are very well blended in the composite membranes. Differential scanning calorimetry revealed that weak interaction possibly decreased the activity of the segment and elevated the T g from 43 °C to 46 °C. From the in vitro dissolution tests, PDLLA as a biodegradable and biocompatible polymer can improve the solubility of FF. The rate of drug release increased with increasing PEG proportion. Furthermore, tensile and nanoindentation tests demonstrated that nanofibers exhibit mechanical properties such as tensile stress (700–2800 KPa), strain (40–120%), and good toughness (0.28–0.98 GPa). In conclusion, PDLLA–PEG–PDLLA nanofibers as a carrier improve the solubility of FF and control drug release.

고분자전해질 막을 위한 나프탈렌 단위를 포함하는 디 및 트리 블록공중합체의 합성 및 특성분석

A fluorinated-sulfonated, hydrophobic-hydrophilic copolymer was planed subsequently synthesized using typical nucleophilic substitution polycondensation reaction. A novel AB and ABA (or BAB) block copolymers were synthesized using sBCPSBP (sulfonated 4,4'-bis[4-chlorophenyl)sulfonyl]-1,1'-biphenyl), DHN (1,5-dihydroxynaphthalene), DFBP (decafluorobiphenyl) and HFIP (4,4'-hexafluoroisopropylidenediphenol). All block copolymers were easily cast and made into clear films. The structure and synthesized copolymers and corresponding membranes were analyzed using GPC (gel permeation chromatography), <TEX>$^1H$</TEX>-NMR (<TEX>$^1H$</TEX> nuclear magnetic resonance) and FT-IR (Fourier transform infrared). TGA (Thermogravimetric analysis) and DSC (differential scanning calorimetry) analysis showed that the prepared membranes were thermally stable, so that elevated temperature fuel cell operation would be possible. Hydrophobic/hydrophilic phase separation and clear ionic aggregate block morpology was confirmed in both triblock and diblock copolymer in AFM (atomic force microscopy), which may be highly related to their proton transport ability. A sulfonated BAB triblock copolymer membrane with an ion-exchange capacity (IEC) of 0.6 meq/g has a maximum ion conductivity of 40.3 mS/cm at <TEX>$90^{\circ}C$</TEX> and 100% relative humidity.

Phototransparency and water vapor sorption properties of ABA‐type triblock copolymers derived from 6FDA‐TeMPD and poly(2‐methyl‐2‐adamantylmethacrylate)

ABSTRACTThe phototransparency and water vapor sorption properties of ABA‐type triblock copolymer membranes derived from 4,4‐(hexafluoroisopropylidene) diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (PI) and poly(2‐methyl‐2‐adamantylmethacrylate) (PMAdMA) were investigated, with focus on the effect of the adamantane component. The phototransparency of PMAdMA‐block‐PI‐block‐PMAdMA [Block(PI/PMAdMA)] was about 10–20% higher than that of poly(methyl methacrylate)‐block‐PI‐block‐Poly(methylmethacrylate) [Block(PI/PMMA)] because the high symmetric structure of adamantane inhibited photoabsorbance. The water vapor solubility of Block(PI/PMAdMA) decreased with increased PMAdMA because the PMAdMA had a hydrophobic property. Interestingly, in all relative‐pressure regions, Block(PI/PMAdMA) with the least PMAdMA content showed a higher solubility coefficient than PI because the high mobility of PMAdMA in Block(PI/PMAdMA) resulted in additional sorption sites in the PI segment. A comparison of Block(PI/PMAdMA) with Block(PI/PMMA) in terms of relative pressure at the beginning of clustering further revealed that cluster formation in Block(PI/PMAdMA) was inhibited compared with Block(PI/PMMA) because bulky structure of adamantane restricted the mobility of the polymer main chain. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43795.

Polymersome Membrane Permeability and Ionic Transport Properties in the Presence of Sub-2nm Carbon Nanotube Porins

Synthetic diblock and triblock copolymer membranes are semi-permeable barriers that are capable of self-assembly into tunable membranes, which have contrasting mechanical properties from biologically derived and synthetic lipid bilayers. These thick and “robust” polymer membranes are typically thicker and have significantly reduced water permeability compared to lipid bilayers. These properties make them valuable alternative membranes for applications requiring exposure to physical stresses such as biosensors, drug delivery, and filtration. Previous attempts to engineer the permeability of these membranes included insertion of protein channels to improve permeably, (eg. Aquaporins), changing the polymer constituent to an inherently leaky polymer (eg. polystyrene-b-polyisocyanoalanine(2-thiophene-3-yl-ethyl)amide (PS-PIAT)), and removal of lipids from a mixed lipid-polymer vesicle following cross-linking and hydrolysis. We report a new strategy for improving permeability of polymer-membranes, based on incorporation of carbon nanotube porins into the polymer matrix. These short CNT pores exhibit the excellent transport properties inherent to carbon nanotubes, but are small enough that they can be easily incorporated into the membrane essentially acting as protein channel mimics. Here, we examine the permeability of diblock co-polymer membranes with and without these CNT pores and report the enhancement of permeability and ion transport characteristics of these novel membrane constructs.

Pervaporation of organic compounds from aqueous mixtures using polydimethylsiloxane‐containing block copolymer membranes

Pervaporation of aqueous mixtures of ethanol, acetone, butanol, isobutanol, and furfural through polystyrene‐b‐polydimethylsiloxane‐b‐polystyrene (SDS) triblock copolymer membranes is reported. These mixtures are important for biofuel production from lignocellulosic feedstocks. Feedstock depolymerization results in the formation of furfural which must be removed before fermentation. Ethanol, butanol, isobutanol, and acetone are important fermentation biofuels. The membrane selectivity of SDS is about unity over a wide range of concentrations of aqueous ethanol mixtures, similar to the membrane selectivity of crosslinked polydimethylsiloxane (PDMS). The permeabilities of butanol, isobutanol, and furfural are larger than those of ethanol and acetone. The volatile organic compound permeability through SDS is similar to or higher than that through PDMS across a broad range of temperatures and feed concentrations is found. More selective and permeable membranes are needed to lower the cost of biofuel purification. The SDS membranes developed are but one step toward improved membranes. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2789–2794, 2015

Polywraplex, Functionalized Polyplexes by Post‐Polyplexing Assembly of a Rationally Designed Triblock Copolymer Membrane

A core–shell structured synthetic carrier, polywraplex, is reported to overcome the hurdles along the inter‐ and intracellular pathways of systemic delivery of siRNA, yet remain structurally simple and easy‐to‐formulate. The core is a cationic polyplex formed of siRNA with polyethylene imine (PEI) and polyspermine‐imidazole‐4,5‐imine (PSI), respectively, and the shell is a self‐assembled unilamella membrane of PEG45‐PCL20‐mototriose‐COO−, a triblock copolymer possessing multicarboxyl saccharide block to guide adsorption to each polyplex surface, a hydrophobic central block to form a protecting layer around the nucleic acid core, and a PEG block functioning as a steric stabilization out‐layer to extend in vivo circulation. The hydrophobic layer limits the anionic charges of the guiding block within a 2D surface to prevent them from penetrating into the polyplex, a common cause for prephagocytic siRNA leaking by polyelectrolytes in vivo. Cell targeting agents may be conjugated to the distal end of the PEG block and assembled on polyplex surface in optimal population. Chemical characterizations comprising consequent fluorescent imaging, dynamic laser scattering, zeta potential, as well as electrophoresis confirm polywraplex formation and its protection to siRNA against leaking and degradation in serum. Cellular and in vivo (mice) assays of biotin‐conjugated polywraplexes suggest prolonged circulation and tumor tissue targeting.