Poly(arylene ether sulfone) multi-block copolymers bearing perfluoroalkylsulfonic acid groups

Perfluorosulfonic acid (PFSA) polymers are the most promising state-of-the-art materials as proton exchange membranes (PEM) for fuel cells, however, there are some drawbacks such as high production cost and hydrothermal stability. Aromatic membranes based on hydrocarbon polymers have been studied as alternatives. Among them, multi-block copolymers seem to be promising to compete with PFSA resulting high proton conductivity even under low RH conditions.[1, 2] In this report, novel sulfonated poly(arylene ether sulfone)s multi-block copolymer membranes containing highly sulfonated hydrophilic blocks were synthesized.[3] Different local concentration of sulfonic acid in their hydrophilic blocks affected chemical and physical properties of the SPAES. To investigate the effects of chemical composition on their membrane properties, different hydrophilic oligomers sharing same hydrophobic blocks gave us exact comparison of effect of hydrophilic blocks. The higher concentration of sulfonic acid groups resulted in higher proton conductivity under certain relative humidity conditions than that of the state-of-the-art perfluorinated sulfonic acid membrane and showed that the well-developed phase separation of SPAES. Moreover, physical properties of theses SPAES including water behavior, humidity dependence of proton conductivity were investigated along with morphology characterizations by transmission electron microscopy (TEM) for PEMFC application. Two types of oligomers, F-terminated and OH-terminated telechelic oligomers, were synthesized by controlling the feed ratio of dihydroxyl- and difluoro-monomers. Their number of repeating unit (X and Y) was analyzed by GPC and 1H NMR. Copolymerization with F-terminated and OH-terminated telechelic oligomers via nucleophilic aromatic substitution, gave high-molecular-weight multi-block PESs. Each block length was controlled to have different values with X5Y10, X10Y10, X20Y10 and X20Y20. The SPAES X10Y10 membrane showed highest proton conductivity than that of our previous random and block copolymers at wide range of humidity. The best balanced membrane was SPAES X10Y5 membrane with high proton conductivity and lower water uptake. Consequently, the SPAES X10Y5 membrane showed high cell performance under various conditions (510 mA/cm2, 290 mA/cm2 @ 0.6V under 80% and 50 % RH conditions at 80℃, respectively). Systematic approaches for developing alternative block SPES membrane for low RH condition will be discussed.

Present research has been conducted for a new series of multiblock copolymers based on hydrophobic oligomer poly (arylene ether sulfone) containing 6F-bisphenol A and hydrophilic oligomer sulfonated poly (arylene ether ketone) containing pendant carboxylic acid group with varying hydrophobic block length. The ionic liquid is embedded into the synthesized multiblock copolymers to fabricate the hybrid multiblock membranes via solution casting method. The copolymers are characterized by 1H NMR, FT-IR and gel permeation chromatography (GPC) techniques. The thermal stability of the membranes has been investigated through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) thermograms. The ionic synergism between the I.L and the acidic groups present in the multiblock copolymer provides a free pathway for the protons to travel and the resulting hybrid membranes exhibit proton conductivity in the range of (0.03 - 0.16) S/cm at 80 °C. Compared with pristine membranes, the hybrid membranes exhibit improved oxidative and mechanical stability. Moreover, the scanning electron microscopy (SEM) investigation depicts better phase separation in hybrid membranes than pristine membranes by forming ionic clusters. The membranes have been tested in H2/O2 fuel cell and their performance is compared with the state-of-art Nafion 117 membrane. For hybrid membranes, with the addition of I.L, the voltage and power densities values increased up to 0.59 V and 0.23 Wcm-2, respectively. These investigations suggest that the synthesized multiblock membranes are promising candidate for proton exchange membrane fuel cells.

A new series of poly(arylene ether sulfone) multiblock copolymers were synthesized by polycondensation of linear and rigid hydrophobic and densely sulfonated hydrophilic oligomers. Thin membranes were prepared therefrom by solution casting and their properties were compared with those of Nafion and other poly(arylene ether sulfone) multiblock copolymers containing perfluorinated biphenylene moieties. The membranes showed good water affinity, high proton conductivity, low hydrogen and oxygen permeability, high mechanical strength, and reasonable oxidative stability. These properties are attractive as an electrolyte for polymer electrolyte membrane fuel cells. It was found that the perfluorinated biphenylene moieties as connecting groups for hydrophilic and hydrophobic blocks affected only slightly the properties of poly(arylene ether sulfone) multiblock copolymer membranes.

Long-chain-branched poly(aryl ether sulfone)-poly(tetrahydrofuran) multiblock copolymers (PES-BPTHF) composed of hard linear and soft branching segments were synthesized from bromo-terminated poly(tetrahydrofuran) and hydroxy-terminated poly(aryl ether sulfone). A study on the effect of concentration on polymerization behavior revealed that soluble powder was obtained at the optimized reaction concentration of 7 wt%. Gelation and intramolecular cyclization were observed at high and low concentrations, respectively. The microphase-separated morphology of PES-BPTHF was confirmed by atomic force microscopy, small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA) measurements. Fewer entangled poly(tetrahydrofuran) segments were detected in PES-BPTHF than in PES-PTHF by SAXS, DMA and tensile measurements. Rheological measurements suggested high chain entanglement of PES-BPTHF in its melt phase. It is interesting to note that the polymer chains in the soft domains become less entangled and more reminiscent of hyperbranched architectures, whereas the overall chain entanglements are increased due to the long-chain-branched structure. Long-chain-branched poly(aryl ether sulfone)-poly(tetrahydrofuran) multiblock copolymers composed of hard linear and soft branching segments were synthesized from bromo-terminated poly(tetrahydrofuran) and hydroxy-terminated poly(aryl ether sulfone). Optimization of the polymerization conditions afforded soluble powder at a reaction concentration of 7 wt%. Microphase-separated morphology was observed for the branched multiblock copolymers. Compared with the corresponding linear multiblock copolymer, the branched polymer chains in the soft domains become less entangled and more reminiscent of hyperbranched architectures, whereas the overall chain entanglements are increased due to the long-chain-branched structure.

Hybrid membranes formed by co-assembly of AxByAx (hydrophilic-hydrophobic-hydrophilic) triblock copolymers into lipid bilayers are investigated by dissipative particle dynamics. Homogeneous hybrid membranes are developed as lipids and polymers are fully compatible. The polymer conformations can be simply classified into bridge- and loop-structures in the membranes. It is interesting to find that the long-time fraction of loop-conformation () of copolymers in the membrane depends significantly on the hydrophilic block length (x). As x is small, an equilibrium always results irrespective of the initial conformation distribution and its value depends on the hydrophobic block length (y). For large x, tends to be time-invariant because polymers are kinetically trapped in their initial structures. Our findings reveal that only symmetric hybrid membranes are formed for small x, while membranes with stable asymmetric leaflets can be constructed with large x. The effects of block lengths on the polymer conformations, such as transverse and lateral spans ( and ) of bridge- and loop-conformations, are discussed as well.

Multiblock copoly(arylene ether sulfone)s with different block lengths and ionic contents are tailored for durable and proton‐conducting electrolyte membranes. Two series of fully aromatic copolymers are prepared by coupling reactions between non‐sulfonated hydrophobic precursor blocks and highly sulfonated hydrophilic precursor blocks containing either fully disulfonated diarylsulfone or fully tetrasulfonated tetraaryldisulfone segments. The sulfonic acid groups are exclusively introduced in ortho positions to the sulfone bridges to impede desulfonation reactions and give the blocks ion exchange capacities (IECs) of 4.1 and 4.6 meq. g−1, respectively. Solvent cast block copolymer membranes show well‐connected hydrophilic nanophase domains for proton transport and high decomposition temperatures above 310 °C under air. Despite higher IEC values, membranes containing tetrasulfonated tetraaryldisulfone segments display a markedly lower water uptake than the corresponding ones with disulfonated diarylsulfone segments when immersed in water at 100 °C, presumably because of the much higher chain stiffness and glass transition temperature of the former segments. The former membranes have proton conductivities in level of a perfluorosulfonic acid membrane (NRE212) under fully humidified conditions. A membrane with an IEC of 1.83 meq. g−1 reaches above 6 mS cm−1 under 30% relative humidity at 80 °C, to be compared with 10 mS cm−1 for NRE212 under the same conditions.

The commercialization of proton exchange membrane (PEM) fuel cells depends largely upon the development of PEMs whose properties are enhanced over current perfluorinated sulfonic acid PEMs. Understanding how a PEM's molecular weight and morphology affect its relevant performance properties is essential to this effort. Changes in molecular weight were found to have little effect on the phase separated morphologies, water uptake, and proton conductivities of random copolymers. Changes in block length, however, have a pronounced effect on multiblock copolymers, affecting surface and bulk morphologies, water uptake, proton conductivity, and hydrolytic stability, suggesting that multiblock copolymer PEM properties may be optimized by changes in morphology.

Conventional amphiphilic block copolymers are macromolecules consisting of at least a hydrophilic segment covalently attached to a hydrophobic segment. They are unique and versatile building blocks in supramolecular polymer chemistry, both for the generation of highly organized, self-assembled structures and for the structural control of material interfaces. In the absence of solvents, the phase-behavior of block-copolymers is sparingly described. In aqueous solutions block copolymers self-assemble into nanoscopic objects. These structures are gaining more and more attention for technical formulations. Self-assembly is simply induced by dissolving dry powder of amphiphilic copolymers in water. This self-assembly process, however, cannot be described solely based on bulk phase behavior and very few experimental phase diagrams of block copolymer/water mixtures have been reported. In order to control, predict and eventually achieve a comprehensive understanding of this process and in particular the formation of vesicles, worm/rod-like micelles and spherical micelles it is important to systematically investigate the phase behavior of block copolymers across the whole water concentration range. We therefore undertook investigations of the self-assembly of two block copolymers. Preliminary encapsulation studies reveal their potential for applications relevant for drug delivery. 
\nThe concentration profile of the identified amphiphilic block-copolymers diluted in aqueous solution was examined across the whole concentration range with four poly(ethylene oxide)-block-poly(γ-methyl-ε-caprolactone) (PEO-b-PMCL) block copolymers keeping the hydrophilic block length constant but varying the hydrophobic lengths. Bulk polymers did not display any ordered morphology. With increasing water concentrations the polymers underwent transitions from lamellar phases to packed vesicles and eventually all polymers self-assembled into vesicles in dilute aqueous solutions. At high concentration the largest polymer organized further into an inverse hexagonal phase prior to self-assembly into a lamellar phase. The smallest block-copolymer also self-aggregated into rod-like micelles and exhibited a hexagonal phase between the packing of the rod-like micelles/vesicles and the lamellar phase.
\nThe concentration profile of phases assembled by amphiphilic block-copolymers diluted in aqueous solution was examined as well across the whole concentration range with three poly(isobutylene)-block-poly(ethylene oxide) block copolymers having the same hydrophobic block length but varying in their hydrophilic lengths. In contrast to PEO-b-PMCL these polymers self-aggregated depending on the hydrophilic length into micelles, worm-like micelles and for the shortest polymer into vesicles. Thus, increasing the polymer concentration lead to a different phase behavior. The largest polymer which solely formed micelles, underwent transitions from packed micelles with a few packed worm-like micelles to a hexagonal phase and finally into a lamellar phase, in contrary to the middle length polymer, which self-aggregated into worm-like micelles. The best to our knowledge, it is the first time that an experimental phase diagram is built such that it displays the formation of worm/rod-like micelles. With the composition studied in here, the worms, with increasing polymer concentration, pack and undergo afterwards into a hexagonal and finally a lamellar phase has been observed. For the shortest polymer the phase behavior was similar to that of vesicles self-assembled by PEO-b-PMCL. In contrast, the pure polymer formed an inverse hexagonal phase.
\nIt was eventually shown that PEO23-PMCl32 can be used to encapsulate both small and large molecules. By adjusting the pH towards acidic conditions the responsiveness of the vesicles could be triggered to release the encapsulated material.

Disulfonated poly(arylene ether sulfone) random copolymers have shown promise as potential candidates for proton exchange membranes. The chemical structure of these copolymers has served as a basis for the molecular design of new random and multiblock copolymers. In random copolymers the sulfonic acid is distributed statistically, while in the multiblock copolymers the chemical structure is designed to have co continuous hydrophilic and hydrophobic domains. The effect of these variables on the transport properties of the membranes was investigated. For the random copolymers, high proton conductivity was observed at higher IEC along with high methanol permeability. But for the multiblock copolymers, it was possible to combine high proton conductivity with low methanol permeability. Improved proton conductivity was observed under partially hydrated conditions for samples with higher block lengths. Self diffusion coefficient of water was also measured by NMR which provided better understanding of the transport process.

New micelle-like polymer aggregates made from PEI–PLGA diblock copolymers: micellar characteristics and cellular uptake

The effects of polymers on the one-dimensional assembly of silica nanospheres (SNSs) in the liquid phase are systematically investigated using nonionic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (abbreviated as PEO-PPO-PEO) triblock copolymers with varying hydrophilic-lipophilic balance (HLB) values. Scanning electron microscopy is employed for morphological observations of the polymer-mediated assemblies of SNSs on the basis of which the optimal pH for 1D assembly (pH(1D)) is determined. To clarify the polymers' effects on the 1D assembly of SNSs, the relationships between pH(1D) and polymers' HLB values, the numbers of hydrophilic EO and hydrophobic PO units, and the relative ratio of N(PO)/N(EO) are examined. Zeta potential measurements are conducted to investigate the electrostatic repulsion among the SNSs in the presence of block copolymers. It is found that the relative hydrophilicity of the block copolymers greatly affects the balance of interactions in the 1D assembly of SNSs. Block copolymers with large HLB values promote the 1D assembly of SNSs under near-neutral pH conditions, whereas the block copolymers with small HLB values promote 1D assembly under basic pH conditions. Therefore, the 1D assembly of SNSs is achieved over an extensive pH range (7.5-9.5) through the employment of block copolymers of different hydrophilic and hydrophobic block lengths.

We report herein the unexpected temperature triggered self-assembly of proteins fused to thermally responsive elastin-like polypeptides (ELPs) into spherical micelles. A set of six ELP block copolymers (ELP(BC)) differing in hydrophilic and hydrophobic block lengths were genetically fused to two single domain proteins, thioredoxin (Trx) and a fibronectin type III domain (Fn3) that binds the α(v)β(3) integrin. The self-assembly of these protein-ELP(BC) fusions as a function of temperature was investigated by UV spectroscopy, light scattering, and cryo-TEM. Self-assembly of the ELP(BC) was unexpectedly retained upon fusion to the two proteins, resulting in the formation of spherical micelles with a hydrodynamic radius that ranged from 24 to 37 nm, depending on the protein and ELP(BC). Cryo-TEM images confirmed the formation of spherical particles with a size that was consistent with that measured by light scattering. The bioactivity of Fn3 was retained when presented by the ELP(BC) micelles, as indicated by the enhanced uptake of the Fn3-decorated ELP(BC) micelles in comparison to the unimer by cells that overexpress the α(v)β(3) integrin. The fusion of single domain proteins to ELP(BC)s may provide a ubiquitous platform for the multivalent presentation of proteins.

Aqueous solutions of both poly(ethylene glycol)/poly(dl-lactic acid) (PEG/PDLLA) and poly(ethylene glycol)/poly(l-lactic acid) (PEG/PLLA) multiblock copolymers underwent "clear sol-to-turbid gel-to-syneresis" transitions as the temperature increased. To investigate the stereoisomeric effect on the phase behavior, PEG/PDLLA and PEG/PLLA multiblock copolymers with a similar block length and total molecular weight were carefully synthesized. Compared with the PEG/PDLLA multiblock copolymer, the PEG/PLLA multiblock copolymer showed a lower critical gel concentration, a lower sol-to-gel transition temperature, and a wider gel window. In addition, the maximal gel modulus of the PEG/PLLA multiblock copolymer (11.0 wt % in water) was 2 times larger than that of the PEG/PDLLA multiblock copolymer. X-ray diffraction spectra, transmission electron microscopic images, and polarizing optical microscopic images suggested the amorphous state for both PEG/PDLLA and PEG/PLLA multiblock copolymer thermogels. 13C NMR spectroscopy, critical micelle concentrations, hydrophobic dye partition, and circular dichroism spectra suggested that the differences in the thermogel properties come from lower dynamic molecular motion and the higher aggregation tendency of the PLLA due to the isotactic localization of the hydrophobic methyl groups rather than crystallization of PLLA.

Novel amphiphilic ABA‐type poly(D‐gluconamidoethyl methacrylate)‐b‐polyurethane‐b‐poly(D‐gluconamidoethyl methacrylate) (PGAMA‐b‐PU‐b‐PGAMA) tri‐block copolymers were successfully synthesized via the combination of the step‐growth and copper‐catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO‐PU‐OH) was synthesized by the step‐growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA‐b‐PU‐b‐PGAMA block copolymers were synthesized via copper‐catalyzed ATRP of GAMA in N, N‐dimethyl formamide at 20°C in the presence of 2, 2′‐bipyridyl using Br‐PU‐Br as macroinitiator and characterized by 1H‐NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by 1H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo‐gravimetric analysis, and differential scanning calorimetric study. Spherical Ag‐nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri‐block copolymer. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The influence of chemical compositions on the properties of sulfonated poly(arylene ether sulfone)‐based proton‐exchange membranes was studied. First, we synthesized three different series of random SPAES copolymers using three kinds of hydrophobic monomers, including 4,4′‐dihydroxyldiphenylether, 2,6‐dihydroxynaphthalene (DHN), and 4,4′‐hexafluoroisopropylidenediphenol (6F‐BPA) to investigate effects of hydrophobic components on the properties of SPAES membranes as proton‐exchange membranes. Random SPAES copolymers with 6F‐BPA showed the highest proton conductivity while random SPAES copolymers with DHN displayed the lowest methanol permeability among the three random copolymers. Subsequently, we synthesized multiblock SPAES using the DHN as a hydrophobic monomer and studied the effect of the length of hydrophilic segments in the multiblock SPAES copolymers on membrane performance. The results indicated that longer hydrophilic segments in the copolymers led to higher water uptake, proton conductivity, and proton/methanol selectivity of membranes even at low humidity. In addition, the morphology studies (AFM and SAXS measurements) of membranes suggested that multiblock copolymers with long hydrophilic segments resulted in developed phase separation in membranes, and ionic clusters formed more easily, thus improving the membrane performance. Therefore, both the kinds of hydrophobic monomers and the length of hydrophilic segments in SPAES copolymers would influence the membranes performance as proton‐exchange membranes. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010