A facile way to prepare crystalline platelets of block copolymers by crystallization-driven self-assembly

Poly(ε-caprolactone)-block-poly[2-(dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) block copolymers were applied to fabricate elongated polymer platelets with axial length of 5–20 μm and thickness of ca. 10 nm by crystallization-driven self-assembly (CDSA). The block copolymer platelets composed of a crystallized PCL layer sandwiched between two PDMAEMA layers were obtained spontaneously by adding methanol, a selective solvent of PDMAEMA, into the block copolymer solution of THF at 25 °C. Therefore, this is a facile approach to generate lamellar nanoobjects of block copolymers. Effects of the block copolymer compositions on the morphologies of platelets were investigated. The presence of PDMAEMA segments along the lamellar surfaces was further confirmed by loading gold nanoparticles. Moreover, PEO-b-PCL-b-PDMAEMA triblock terpolymer could form spindle platelets by this approach. The crystalline platelets were characterized by the transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD).     

Tailoring the morphology of self-assembled block copolymer hollow fiber membranes

Isoporous asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hollow fiber membranes were successfully made by a dry-jet wet spinning process. Well-defined nanometer-scale pores around 20–40 nm in diameter were tailored on the top surface of the fiber above a non-ordered macroporous layer by combining block copolymer self-assembly and non-solvent induced phase separation (SNIPS). Uniformity of the surface-assembled pores and fiber cross-section morphology was improved by adjusting the solution concentration, solvent composition as well as some important spinning parameters such as bore fluid flow rate, polymer solution flow rate and air gap distance between the spinneret and the precipitation bath. The formation of the well-organized self-assembled pores is a result of the interplay of fast relaxation of the shear-induced oriented block copolymer chains, the rapid evaporation of the solvent mixture on the outer surface and solvent extraction into the bore liquid on the lumen side, and gravity force during spinning. Structural features of the block copolymer solutions were investigated by small-angle X-ray scattering (SAXS) and rheological properties of the solutions were examined as well. The scattering patterns of the optimal solutions for membrane formation indicate a disordered phase which is very close to the disorder-order transition. The nanostructured surface and cross-section morphology of the membranes were characterized by scanning electron microscopy (SEM). The water flux of the membranes was measured and gas permeation was examined to test the pressure stability of the hollow fibers.     

A rheometry method to assess the evaporation-induced mechanical strength development of polymer solutions used for membrane applications

Rotational and oscillatory shear rheometry were used to quantify the flow behavior under minimal and significant solvent evaporation conditions for polymer solutions used to fabricate isoporous asymmetric membranes by the self-assembly and non-solvent induced phase separation (SNIPS) method. Three different A-B-C triblock terpolymer chemistries of similar molar mass were evaluated: polyisoprene-b-polystyrene-b-poly(4-vinylpyridine) (ISV); polyisoprene-b-polystyrene-b-poly(N,N-dimethylacrylamide) (ISD); and polyisoprene-b-polystyrene-b-poly(tert-butyl methacrylate) (ISB). Solvent evaporation resulted in the formation of a viscoelastic film typical of asymmetric membranes. Solution viscosity and film viscoelasticity were strongly dependent on the chemical structure of the triblock terpolymer molecules. A hierarchical magnitude (ISV > ISB > ISD) was observed for both properties, with ISV solutions displaying the greatest solution viscosity, fastest film strength development, and greatest strength magnitude. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47038.     

Critical flux in cross-flow ultrafiltration of protein solutions

The effect of solute size relative to membrane pore size on the critical flux during the ultrafiltration of protein solutions was investigated using the constant pressure method. Hydrophilic regenerated cellulose membranes with a cut-off of 10, 30 and 100 kg mol⁻¹, model proteins and skimmed milk solutions were used. The critical flux mainly increased with the pore size of the ultrafiltration membrane. The lowest critical fluxes, 40-50 L m⁻²h⁻¹, were obtained with the retentive 10 kg mol⁻¹ cut-off membrane. This membrane had a very low permeability and, thus, the critical fluxes were achieved at high transmembrane pressures (TMP): 1.7-2.3 bar. With the 100 kg mol⁻¹ cut-off membrane critical fluxes were obtained at 0.2 bar TMP, which were around 100 L m⁻² h⁻¹, slightly declining with increasing protein molar mass. In skimmed milk experiments the permeate flux decreased when the protein molecules were enzymatically split to peptides. A critical flux for skimmed milk solution could not be found unless the protein concentration was diluted to 0.3-w% or lower. The results with model proteins were then compared to those obtained with skimmed milk resulting in β-lactoglobulin being the worst foulant.     

Partially sulfonated poly(arylene ether sulfone)-b-polybutadiene for proton exchange membrane

A novel block copolymer based on poly(arylene ether sulfone)-b-polybutadiene (SPAES-b-PB) was synthesized and its flexible segment was sulfonated by electrophilic addition reaction with acetyl sulfate. This could be a new approach to prepare suitable alternative proton exchange membranes to Nafion^®. Only a single glass transition temperature (T_g) of copolymer measured by differential scanning calorimeter (DSC) indicated good compatibility between PAES block and PB block. A tough and transparent membrane based on SPAES-b-PB exhibited higher proton conductivity (0.0302 S/cm at 25 °C and 100% relative humidity) even with relatively low ion exchange capacity (IEC) of 0.624 mmol/g compared to other sulfonated block copolymer membranes such as sulfonated polystyrene-b-poly(ethylene-ran-butylene)-b-polystyrene (SSEBS), sulfonated poly(styrene-isobutylene-styrene) (S-SIBS), sulfonated hydrogenated poly-butadiene-styrene copolymer (HPBS-SH) as a result of selected sulfonation of the flexible segments facilitating sulfonated groups to aggregate to form ion-rich channels.     

Thermo-Responsive Ultrafiltration Block Copolymer Membranes Based on Polystyrene-block-poly(diethyl acrylamide)

Within the present work, a thermo-responsive ultrafiltration membrane is manufactured based on a polystyrene-block-poly(diethyl acrylamide) block copolymer (BCP). The poly(diethyl acrylamide) block segment features a lower critical solution temperature (LCST) in water, similar to the well-known poly(N-isopropylacrylamide), but having increased biocompatibility and without exhibiting a hysteresis of the thermally induced switching behavior. The BCP is synthesized via sequential “living” anionic polymerization protocols and analyzed by ¹H-NMR spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The resulting morphology in the bulk state is investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) revealing the intended hexagonal cylindrical morphology. The BCPs form micelles in a binary mixture of tetrahydrofuran and dimethylformamide, where BCP composition and solvent affinities are discussed in light of the expected structure of these micelles and the resulting BCP membrane formation. The membranes are manufactured using the non-solvent induced phase separation (NIPS) process and are characterized via scanning electron microscopy (SEM) and water permeation measurements. The latter are carried out at room temperature and at 50 °C revealing up to a 23-fold increase of the permeance, when crossing the LCST of the poly(diethyl acrylamide) block segment in water.     

Investigation of nanostructures and properties of sulfonated poly(arylenethioethersulfone) copolymer as proton conducting materials by small angle neutron scattering

Sulfonated poly(arylenethioethersulfone) copolymer (SPTES-50), a promising candidate material for proton exchange membrane fuel cell (PEMFC), exhibited excellent thermal stability, high proton conductivity (135 mS/cm at 85 °C, 85% relative humidity), and electrochemical property. Small angle neutron scattering (SANS) of fully hydrated SPTES-50 membranes revealed the presence of embedded spherical nanodomains containing ionic group and water within the polymer membranes. The polydispersity of the nanoscale structure limited scattering contrast between the polymer backbone and sulfonated groups, and precluded analysis of intermediate and large scattering vectors in terms of the polymer-water interface structure. Inter-cluster correlations associated with the large extent of water absorption in the fully hydrated SPTES-50 membranes were accounted by Percus-Yevick liquid-like ordering of polydispersed hard sphere model with Schulz polydispersity approximation. Approximation of their low q upturn with an exponential decay results in a decay of −3 at 25 °C accounted for inter-cluster correlations which changed to a decay of −1.1 at 55 °C and 77 °C. This indicated a change in morphology upon increase of temperature such as to fractal morphology or an interconnected cylindrical network. The scattering patterns don't exhibit any further changes within examined range of q when the temperature increased from 55 °C to 77 °C. The number density of ionic clusters remained approximately constant (∼1.1818 × 10¹⁷ cm³), which indicated that additional water adsorbed by the polymer at the elevated temperature did not result in substantial coalescence of the clusters. Transmission electron microscopy (TEM) observation of the silver exchanged SPTES-50 membranes exhibited aggregates of Ag⁺ embedded within the dry membranes which can be approximated by isolated spheres.     

Photophysical properties and self-assembly of triblock copolymer with complexes of positively charged PDMAEMA and oppositely charged chromophores

The self-assembly and photophysical properties of a triblock copolymer with complex mid-block in THF and aqueous solution were investigated in this research. Poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(2-(dimethylamino ethyl methacrylate)-block- poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA–b–PDMAEMA–b–PPEGMA) triblock copolymer was synthesized by subsequent atom transfer radical polymerizations (ATRP) of DMAEMA and PEGMA. The PDMAEMA blocks were quaternized by a reaction with iodomethane. The complex of the positively charged PDMAEMA chain unit and sodium salt of 1-pyrenebutyric acid was prepared by mixing equimolar amount of the two components in THF/water mixture. Transmission electron microscopy and fluorescence technique results show that the triblock copolymer chains self-assemble into micelles in THF at high concentration. The critical aggregation concentration (CAC) of the triblock copolymer in THF determined by fluorescence technique is 6.8 × 10^?5 M. The triblock copolymer was also able to self-assemble into micelles in water. The value of CAC of the triblock copolymer in water is 2.0 × 10^?5 M. The photophysical properties and self-assembly structures of the triblock copolymer in aqueous solutions were influenced by added sodium chloride. After salt addition, a transition of the assembled structures from micelles to hollow structures was observed.     

Polymerized ionic liquid diblock copolymers with long alkyl side-chain length

A polymerized ionic liquid (PIL) diblock copolymer with a long alkyl side-chain, poly(MMA-b-MUBIm-Br), was synthesized at various compositions from an ionic liquid monomer, (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bromide) (MUBIm-Br), and a non-ionic monomer, methyl methacrylate (MMA). The PIL diblock copolymer was synthesized via post-functionalization from its non-ionic precursor PIL diblock copolymer, poly(MMA-b-BrUMA) (BrUMA = 11-bromoundecyl methacrylate), which was synthesized via the reverse addition fragmentation chain transfer (RAFT) polymerization technique. Differential scanning calorimetry reveals two distinct constant glass transition temperatures (T_gs) with a low PIL segment T_g. These PIL block copolymers result in easily processable, flexible, transparent films with high mechanical strength. A high bromide ion conductivity of 64.85 mS cm⁻¹ at 80 °C and 90% RH was measured for the PIL diblock copolymer with an ion exchange capacity (IEC) of 1.44 meq/g (23.3 mol% MUBIm-Br). Interestingly, this result was three times higher than its analogous PIL homopolymer (2.75 meq/g; 100 mol% MUBIm-Br) and an order of magnitude higher than a PIL block copolymer from a previous study with similar chemistry, similar IEC, higher water content, but shorter alkyl side-chain length. Ion conductivity did not scale as expected with water content, which is unusual for water-assisted ion transport (e.g., protons, hydroxide, chloride) in ion-containing polymers, and therefore suggests other mechanisms that impact ion transport in PIL block copolymers.     

Original route to polylactide–polystyrene diblock copolymers containing a sulfonyl group at the junction between both blocks as precursors to functional nanoporous materials

Novel functionalized nanoporous polymeric materials could be derived from poly(D,L-lactide)-block-polystyrene (PLA-b-PS) diblock copolymers with a sulfonyl group at the junction between both blocks were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) using a synthetic difunctional initiator through a three-step sequential methodology. Different ω-bromo PLA polymers with various molar masses ranging from 3640 to 11,440 g mol⁻¹ were first produced by coupling ω-hydroxy PLA precursors to a chlorosulfonyl-functionalized ATRP initiator previously prepared, thus leading to the formation of suitable macroinitiators for the subsequent ATRP polymerization of styrene. Consequently, PLA-b-PS diblock copolymers were obtained with a finely tuned PLA volume fraction (f_PLA) in order to develop a microphased-separation morphology. The resulting copolymers as well as the intermediate compounds were carefully analyzed by size exclusion chromatography and ¹H NMR. Upon shear flow induced by a channel die processing, oriented copolymers were generally afforded as characterized by small-angle-X-ray scattering (SAXS). Such copolymers were finally submitted to mild alkaline conditions so as to hydrolyze the sacrificial PLA block, and the presence of the sulfonic acid functionality on the pore walls of the resulting nanoporous materials was evidenced by means of a post-modification reaction consisting in the corresponding sulfonamide formation.     

Synthesis of novel poly(ethylene-ter-1-hexene-ter-dicyclopentadiene)s using bis(β-enaminoketonato)titanium catalysts and their applications in preparing polyolefin-graft-poly(?-polycaprolactone)

Novel terpolymers containing ethylene, 1-hexene and dicyclopentadiene (DCPD) were synthesized using bis(β-enaminoketonato)titanium catalysts [PhNC(R₂)CHC(R₁)O]₂TiCl₂ (1a: R₁ = Ph, R₂ = CF₃; 1b: R₁ = CF₃, R₂ = CH₃). In the presence of modified methylaluminoxane, these catalysts afforded terpolymers with a broad range of monomer compositions and unimodal molecular weight distributions. ¹³C NMR spectra reveal the exclusive insertion manner of DCPD maintained under various reaction conditions. DSC results show the melting temperature and the glass transition temperature are very sensitive to the terpolymer composition and the morphology can be easily tuned from semicrystalline state to amorphous state. With ethylene/1-hexene/DCPD molar ratio about 67/28/5, the terpolymer exhibits low glass transition temperature (T_g = −50 °C) and has a great potential to serve as polyolefin elastomer. Additionally, the terpolymer containing 4.3 mol% 1-hexene and 1.6 mol% DCPD was served as the “reactive intermediate polyolefin” for PCL graft reaction. The composition of graft copolymer was well controllable and high graft efficiency was observed. The microscopy studies in conjunction with the tensile tests revealed that PCL graft copolymer is the effective compatibilizer for polyethylene/polar polymer blends by improving the interfacial adhesion between separated phases.     

Synthesis and characterization of well-defined hydrophilic block copolymer brushes by aqueous ATRP

Homopolymer brushes of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA) and poly(N-isopropylacrylamide)(PNIPAM) grown on atom transfer radical polymerization (ATRP) initiator functionalized latex particles were used as macroinitiators for the synthesis of PDMA-b-PNIPAM/PMEA, PMEA-b-PDMA/PNIPAM and PNIPAM-b-PDMA block copolymer brushes by surface initiated aqueous ATRP. The grafted homopolymer and block copolymer brushes were analyzed for molecular weight, molecular weight distribution, chain grafting density, composition and hydrodynamic thickness (HT) using gel permeation chromatography-multi-angle laser light scattering, ¹H NMR, particle size analysis and atomic force microscopy (AFM) techniques. The measured graft molecular weight increased following the second ATRP reaction in all cases, indicating the second block had been added. Chain growth depended on the nature of the monomer used for block copolymerization and its concentration. Unimodal distribution of polymer chains in GPC with non-overlap of molar mass-elution volume curves implied an efficient block copolymerization. This was supported by the increase in HT measured by particle size analysis, equilibrium thickness observed by AFM and the composition of the block copolymer layer by ¹H NMR analysis, both in situ and on cleaved chains in solution. ¹H NMR analysis of the grafted latex and cleaved polymers from the surface demonstrated that accurate determination of the copolymer composition by this method is possible without detaching polymer chains from surface. Block copolymer brushes obey the same power law dependence of HT on molecular weight as homopolymer brushes in good solvent conditions. The NIPAM-containing block copolymer brushes were sensitive to changes in the environment as shown by a decrease in HT with increase in the temperature of the medium.     

Poly(vinylidene fluoride) ultrafiltration membranes containing hybrid silica nanoparticles: Preparation,characterization and performance

Poly(vinylidene fluoride) (PVDF) ultrafiltration membranes were prepared by immersion precipitation method using poly(hydroxyethyl methacrylate)-block-poly(methyl methacrylate) grafted silica (PHEMA-b-PMMA@SiO₂) nanoparticles as additives. The hybrid nanoparticles were synthesized by the surface initiated atom transfer radical polymerization (SI-ATRP), and they were characterized in detail by FT-IR, TEM, DLS and GPC. Results confirm that core–shell structure is formed after grafting PHEMA-b-PMMA brushes on the silica nanoparticles. Their average hydrodynamic diameter also increases with the prolongation of grafting time. After blending PVDF with the hybrid silica nanoparticles, the composite PVDF membranes exhibit high porosity and improved water permeation. Especially, when the molecular weight is 1.73 × 10⁵ g/mol for PHEMA-b-PMMA on the hybrid nanoparticles, the water flux of the PVDF composite membrane is 2.5 times than that of the control PVDF membrane, while the rejection to bovine serum albumin (BSA) remains at a high level (>90%). In addition, all the composite PVDF membranes show lower BSA adsorption and larger water flux recovery ratio than the control PVDF membrane. The improvement of membrane performance is attributed to the good hydrophilicity of PHEMA-b-PMMA@SiO₂ nanoparticles. Our results suggest that PHEMA-b-PMMA@SiO₂ nanoparticles with moderate molecular weight of PHEMA-b-PMMA are suitable for the property optimization of PVDF-based composite membranes.     

Functionalized organic nanoparticles from core-crosslinked poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer micelles

Surface-functionalized polymeric nanoparticles were prepared by: a) self-assembly of poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer (PVBCB-b-PB) to form spherical micelles (diameter: 15-48 nm) in decane, a selective solvent for PB, b) crosslinking of the PVBCB core through thermal dimerization at 200-240 °C, and c) cleavage of the PB corona via ozonolysis and addition of dimethyl sulfide to afford aldehyde-functionalized nanoparticles (diameter: ∼16-20 nm), along with agglomerated nanoparticles ranging from ∼30 to ∼100 nm in diameter. The characterization of the diblock copolymer precursors, the intermediate micelles and the final surface-functionalized crosslinked nanoparticles was carried out by a combination of size exclusion chromatography, static and dynamic light scattering, viscometry, thermogravimetric analysis, ¹H NMR and FTIR spectroscopy and transmission electron microscopy.     

Migration of additives in polymer coatings: fluorinated additives and poly(vinylidene chloride)-based matrix

In order to combine the properties of polymers based on vinylidene chloride (VC₂) (barrier properties towards many gases) and fluorinated polymers (low surface energy, improvement of the chemical resistance), a diblock terpolymer poly(VC₂-co-MA)-b-(PFDA) was synthesized by RAFT process. The first block is a statistical copolymer of vinylidene chloride (VC₂) and methyl acrylate (MA) (M_n=6800 g mol⁻¹ and PDI=1.4), the second block is a homopolymer of 1H,1H,2H,2H-perfluorodecyl acrylate (FDA). The diblock terpolymer, when used in a coating formulation based on a poly(VC₂-co-MA) matrix, migrates towards the surface of the coating and fluorinated moieties are located at the surface. The migration of the additive was clearly shown by scanning electron microscopy EDX and by measurements of surface energy, and the influence of the nature of the solvents used to prepare the coating was clearly established. These results indicate that the driving force for the migration is the surface energy of the additive.     

Influence of compatibility between sol and intermediate layer on the performance of yttria-stabilized zirconia nanofiltration membrane

This paper reports the synergistic effect of the sol and intermediate layer on the performance of yttria-stabilized zirconia (YSZ) nanofiltration (NF) membranes. We have focused on the characterization of the microstructure, pure water permeance, and molecular weight cut-off (MWCO) of the NF membranes derived from zirconia sols of different precursor concentrations on two types of supported ZrO₂ ultrafiltration (UF) membranes. We found that the performance of YSZ membranes strongly depends on the sol concentration and the pore size of the intermediate layer. In addition, YSZ gel membrane formation was found to follow the filtration process. Therefore, it is essential to maintain the compatibility between the sol and intermediate layer to fabricate high-performance NF membranes. A crack-free thin YSZ layer with an MWCO of 816 Da (pore size: 1.4 nm) and a water permeance of 25 L m^-2 h^-1 bar^-1 was fabricated using a precursor concentration of 0.03 mol/L, on ZrO₂ UF membrane with a pore size of 5.5 nm. The YSZ NF membrane exhibited a relatively high retention rate towards MgCl₂ (71%), whereas a lower retention rate was observed for NaCl (35%).     

Complex micelles with a responsive shell for controlling of enzymatic degradation

Complex polymeric micelles with a PLA core and a mixed PEG/PNIPAM shell were prepared by self-assembly of two block copolymers: poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) and poly(N-isopropylacrylamide)-b-poly(lactic acid) (PNIPAM-b-PLA). Using ¹H NMR spectroscopy and dynamic light scattering, the micellization and the enzymatic degradation status were characterized. At 25 °C, the PNIPAM block is hydrophilic and the PLA core is prone to the enzymatic degradation, resulting in the disassembly of the micelles. While increasing the temperature to 45 °C, the PNIPAM collapsed onto the PLA core, protecting the PLA core from the attack by the enzyme, and the micelles exhibit a resistance to the enzymatic degradation. Furthermore, the enzymatic degradation rate of the micelles can also be tuned by changing the ratio of PEG to PNIPAM. With increasing content of PNIPAM, the conformation of the collapsed PNIPAM changes from patchy domains to a continuous and dense layer, and the enzyme accessibility to the PLA core is changed.     

Synthesis and self-assembly of a novel Y-shaped copolymer with a helical polypeptide arm

A novel biodegradable Y-shaped copolymer, poly(l-lactide)₂-b-poly(γ-benzyl-l-glutamic acid) (PLLA₂-b-PBLG), was synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG-NCA) with centrally amino-functionalized poly(l-lactide), PLLA₂-NH₂, as a macroinitiator in a convenient way. The Y-shaped copolymer and its precursors were characterized by ¹H NMR, FT-IR, GPC, WAXD and DSC measurements. The self-assembly of the PLLA₂-b-PBLG copolymer in toluene and benzyl alcohol was examined. It was found that the self-assembly of the copolymer was dependent on solvent and on relative length of the PBLG block. For a copolymer with PLLA blocks of 26 in total degree of polymerization (DP), if the PBLG block was long enough (e.g., DP = 54 or more), the copolymer/toluene solution became a transparent gel at room temperature. In benzyl alcohol solution, only PLLA₂-b-PBLG containing ca. 190 BLG residues could form a gel; those with shorter PBLG blocks (e.g., DP = 54) became nano-scale fibrous aggregates and these aggregates were dispersed in benzyl alcohol homogeneously. Copolymers with short PBLG blocks behaved like a pure PLLA both in toluene and in benzyl alcohol. These experimental results were discussed and explained by virtue of the helical conformation of PBLG and the interactions between the solvents and the PLLA and/or PBLG segments.     

Poly(sulfonated phenylene)-block-poly(arylene ether sulfone) copolymer for polymer electrolyte fuel cell application

Novel poly(2-(3-sulfo)benzoyl-1,4-phenylene)-block-poly(arylene ether sulfone) copolymers (PSP-b-PAESs) were successfully synthesized by Ni(0)-catalyzed copolymerization of 2,5-dichloro-3′-sulfo-benzophenone (DCSB) and chlorobenzophenone-endcapped oligo(arylene ether sulfone). Their physical property, morphology and polymer electrolyte fuel cell (PEFC) performance were investigated compared to those of the DCSB-based random copolymers and Nafion112. PSP-b-PAES with a measured ion exchange capacity (IEC) of 1.82 meq g^?1, of which the hydrophilic/hydrophobic block lengths were evaluated as 17/8.4, showed the relatively small number of water molecules sorbed per sulfonic acid group (λ = 15) in water and the anisotropic membrane swelling with 2.4 times larger through-plane swelling than in-plane one, whereas it showed the almost isotropic proton conductivity. The PSP-b-PAES exhibited a microphase-separated structure composed of hydrophobic and hydrophilic domains, whereas the random copolymers exhibited a homogenous morphology. The PSP-b-PAES had the larger proton conductivity than the random copolymer with an IEC of 2.01 meq g^?1, especially under the low relative humidities. Even at a low humidification of 17% RH at 90 °C and 0.2 MPa, the PSP-b-PAES exhibited the high PEFC performance; namely, cell voltage of 0.69 V at load current density of 0.5 A cm^?2 and maximum output of 0.73 W cm^?2, which were much higher than those at 30% RH for the random copolymer (0.65 V and 0.51 W cm^?2) and Nafion112 (0.70 V and 0.61 W cm^?2). The PSP-b-PAES showed the fairly high durability of 750 h under PEFC operation at 90 °C in spite of the relatively low molecular weight. PSP-b-PAESs have the high potential as polymer electrolyte membrane for PEFC applications.     

Morphology of sulfonated polyarylenethioethersulfone random copolymer series as proton exchange fuel cells membranes by small angle neutron scattering

Sulfonated polyarylenethioethersulfone (SPTES) copolymers with high proton conductivity (100-215 mS/cm at 65 °C, 85% relative humidity) are promising potential proton exchange membrane (PEM) for fuel cells. Small angle neutron scattering (SANS) of the hydrated SPTES copolymer membranes at 25 °C exhibit a nanostructure which can be approximated by correlated polydisperse spherical aggregates containing water molecules with liquid-like ordering (Percus Yevick approximation) and large scale water pockets. The ionic domain radius and the volume packing density of the aggregates present in the hydrated SPTES copolymer membranes at 25 °C increased with increasing degree of sulfonation. SPTES-80 with highest degree of sulfonation (71.6%) showed a Guinier plateau at the very low q range (q < 1 × 10⁻⁴ 1/Å) indicating presence of isolated large scale morphology (R_g = 1.3 ± 0.18 micron). The radius of spherical ionic aggregates present in the hydrated SPTES-50 and SPTES-60 copolymer membranes increased with increasing temperature to 55 °C, but the large scale morphology changed to a fractal network. Further increase of the sulfonation degree to 63.3% and 71.6% (SPTES-70 and SPTES-80) resulted in a substantial morphology change of the spherical aggregates to an irregular bicontinuous hydrophobic/hydrophilic morphology for the hydrated SPTES-70 and SPTES-80 copolymer membranes at 55 °C. Presence of ionic maxima followed by a power law decay of −4 for SPTES-70 and SPTES-80 copolymer membranes was attributed to the bicontinuous phase morphology at high degree of sulfonation and elevated temperature (55 °C). The disruption of the larger scale fractal morphology was characterized by significant decrease in the intermediate scattering intensity. Hydrophobic and hydrophilic domains were separated distinctly by sulfonic groups at the interface showing as power law decay of −4 for all hydrated SPTES copolymers.