Polysulfone Backbone Research Articles

Synthesis and Characterization of Zwitter ion Functionalized Polysulfone Membrane

AbstractThe main target of the present research work is synthesis of structurally modified polysulfone (PSF) membrane with good anti‐fouling property. Fouling is a big problem in polymeric membrane field. This can be reduced by introducing the zwitter ionic structure on the polymeric backbone. In this research work, anti‐fouling of PSF membrane was taken as s challenge and successfully done via Friedel‐Crafts (FC) alkylation reaction. For the sake of comparison, the FC alkylation reaction of chloroethylamine (CEA) and chloroaceticacid (CAA) onto PSF backbone was done in a single step and two step reactions in the presence of AlCl3 as a catalyst. The structurally modified PSF was characterized by FT‐IR spectrum, 1H‐NMR spectrum, XPS, EDX, SEM, DSC, TGA, WCA and POM. The porosity and antimicrobial properties of simultaneously acid and amine functionalized PSF membrane was tested. The single step reaction exhibited a peak in the FT‐IR spectrum at 1669 cm−1 corresponding to the zwitter ionic structure. The same peak was absent in the two step reaction. The PSF4 system showed the lowest WCA of 32.4° and confirmed the increase in hydrophilicity of the membrane material. The thermal stability of the PSF before and after the structural modification reaction was internally analyzed and compared with the literature values.

Micro-phase separation promoted by electrostatic field in electrospinning of alkaline polymer electrolytes: DFT and MD simulations

Solution electrospinning effectively constructs long-range ionic channels in alkaline polymer electrolytes, however, the function of electrostatic field on micro-phase separation is hardly well interpreted merely through experiments. Herein, via density functional theory (DFT) and molecular dynamics (MD) simulation, it is found that non-covalent interactions among solvent-cation-backbone play important roles on ionic aggregation, and are greatly influenced by electrostatic field. During electrospinning process, the electrostatic field breaks the intramolecular π-π stacking between imidazolium cation (Im+) and benzene ring on polysulfone (PSF) backbone, contributing to Im+ aggregation. N, N-Dimethylformamide (DMF) solvent forms multiple H-bonds and π-π stacking with PSF backbone, making the PSF fold back toward the opposite direction of Im+ and promoting hydrophobic aggregation. Moreover, Im+-DMF interactions are enhanced by electrostatic fields, which weakens the interchain interactions originated from Im+-Cl− electrostatic interactions, and induces Im+ groups toward the outer layer of the nanofiber during radial evaporation of DMF, constructing continuous long-range ionic channels.

Amphiphilic cone-shaped cationic calix[4]arene composite anion exchange membranes with continuous ionic channels

A novel amphiphilic cone-shaped inducer, tetra-quaternized tetraoctyloxycalix[4]arene (TQCX), is proposed to create continuous ionic channels in an anion exchange membrane (AEM). Via molecular dynamics simulation, it was found that four upper-rim cationic groups induce ionic aggregation via electrostatic interactions, while four lower-rim hydrophobic octyl side chains promote the clustering of hydrophobic domains via van der Waals interactions with the polymer backbone. The core cavity in TQCX introduces additional free volume to connect hydrophilic domains. At the optimal TQCX content of 3 wt%, the ionic clusters with a diameter of ∼12 nm are induced, and even linearly arranged to construct continuous ionic channels with a length up to ∼300 nm. Besides, TQCX also aggregates to form the ion-rich nanoparticles with the size of ∼500 nm, which also assist in the construction of interconnected hydroxide-conducting pathways. Consequently, hydroxide conductivity of the composite membrane yields a 70% improvement at 3 wt% TQCX over that of the pristine membrane, achieving the top level among the reported main-chain-type AEMs based on the polysulfone backbone.

Methoxy groups increase water and decrease salt permeability properties of sulfonated polysulfone desalination membranes

A promising desalination membrane material, sulfonated polysulfone, was structurally modified to increase its water/salt transport selectivity. The structural modification was achieved by adding methoxy groups to the polymer backbone. This modification simultaneously increased water permeability and decreased salt permeability. These changes in properties are both favorable for desalination applications, and they may result from changes in polymer density and the free volume element size distribution. Relative permittivity and salt sorption data for these charged polysulfones suggest that Donnan exclusion may influence salt sorption properties to a greater extent than electrostatic or dielectric exclusion forces, which is reasonable for charged polymers. The Donnan-Manning model did not quantitatively describe the salt sorption properties of the sulfonated polysulfone materials perhaps due to a combination of low water content and a heterogeneous distribution of fixed charge groups throughout the polymer. Interestingly, addition of methoxy groups to the charged polysulfone backbone more strongly influenced the diffusion properties than the sorption properties, and this observation may be important to guide the engineering of highly selective polymeric materials for desalination applications.

A rod-coil grafts strategy for N-spirocyclic functionalized anion exchange membranes with high fuel cell power density

N-spirocyclic cations possess double-cyclic non-planar structure that exhibit the highest alkali stability among quaternary ammonium cations, however, the extremely rigidity usually causes fragile membranes and poor conductivity. In this work, a rod-coil grafts design is proposed for N-spirocyclic anion exchange membranes (AEMs), in which microphase separation of the hydrophilic N-spirocyclic rod grafts is significantly improved by the hydrophobic aggregation of the flexible alkyl coil grafts with polysulfone backbone. Molecular dynamic simulations indicate that the coil grafts contribute to microphase separation but fill in free volume to reduce water reservoir, therefore the rod-coil grafts design provides a way to evaluate the effects of microphase separation and free volume on conductivity. The increasing conductivity with the length of coil grafts suggests a greater contribution of good microphase separation to OH− conduction. With optimized n-octylamine hydrophobic coil graft length, the N-spirocyclic AEM exhibits toughness (elongation at break of about 28.7%) and high OH− conductivity (136.2 mS cm−1 at 80 °C), resulting in high power density (850.1 mW cm−2), which is far greater than that assemble with other N-spirocyclic AEMs, and also bring N-spirocyclic AEMs into the top level of the cycloaliphatic AEMs reported in literatures.

Hydration, Ion Distribution, and Ionic Network Formation in Sulfonated Poly(arylene ether sulfones)

We use molecular dynamics simulations to probe hydration, ion spacing, and cation-anion interaction in two sulfonated polysulfones with different ion distributions along the polymer backbone. At room temperature, these polymers remain in a glassy state even with water contents more than 10%. At the equilibrium water uptake, the ions exhibit a similar level of hydration as they would in their saturated aqueous solution. The framework of Manning's limiting law for counterion condensation is used to examine ionic interactions in the simulated polysulfones. The dielectric constant that the ions experience can be well approximated by a volume-weighted average of the dielectric constants of the polymer backbone and water. Our results show that a reasonable estimate of the average inter-ion distance, b, is obtained by using the distance where the sulfonate-sulfonate coordination number reaches 1. The spacing of the sulfonate ions along the polysulfone backbone plays a role in determining their spatial distribution inside the hydrated polymer. As a result, the value of b is slightly larger for polymers where the sulfonate ions are more evenly spaced along the backbone, which is consistent with experimental evidence. The simulations reveal that the sulfonate ions and sodium counterions form fibrillar aggregates at water contents below the equilibrium water uptake. Such extensive ionic aggregates are expected to facilitate ion transport in sulfonated polysulfone membranes, without the need for long-range chain motion as in the case of traditional rubbery ionic polymers. Our estimates for the dielectric constant and b are used in conjunction with Manning's theory to estimate the fraction of counterions condensed to the fixed ions. The prediction of Manning's theory agrees well with the simulation result.

Preparation of self-crosslinking anion exchange membrane with acid block performance from side-chain type polysulfone

In this work, a novel strategy is designed with the goal of further improving comprehensive performance of anion exchange membrane (AEM). That is, some double-functional monomers with both anion exchange groups and unsaturated double bond pendants, such as N, N-Dimethylallylamine (DMAA), N-Allylmethylamine (AMA), are introduced into Polysulfone backbone in terms of side chains firstly, and then heat-initiated crosslinking occurs during the membrane formation along with the evaporation of solvent and aggregation of polymer chains. For comparison, the conventional AEM is also prepared by heterogeneous amination. Series of characterizations, including chemical composition analyses and micro-structure observations, confirm that desired AEMs are fabricated successfully with a simultaneous occurrence of micro-phase segregation and self-crosslinking. Furthermore, the water uptake, membrane resistance, membrane homogeneity, membrane permselectivity, and thermal, mechanical and chemical stability are investigated to understand the effects of the formed membrane structure. Especially, as-prepared AEMs display outstanding acid block performances. For example, strong base DMAA-4 increase the current efficiency of ED-based acid enrichment to 98.63%, far ahead of that of conventional TMA-4. This work not only indicates acid block performance can be imparted to the strong base AEM but also make it possible to perform the ED-based reclamation of waste acid economically and efficiently.

High Temperature Polymer Electrolyte Membrane Achieved By Grafting Poly(1-vinylimidazole) on Polysulfone for Fuel Cell Applications

High temperature polymer electrolyte membranes with phosphoric acid doping are crucial materials of high temperature fuel cells. However, the evolution of the type membrane is suffering from the trade-off between proton conductivity and mechanical strength, because high proton conductivity requires high phosphoric acid doping level, which will reduce the mechanical properties due to the plasticization of phosphoric acid on polymer backbone. Here, a new strategy is employed to respond to the unresolved challenges by grafting poly(1-vinylimidazole) as phosphoric acid doping sites on polysulfone backbone via atom transfer radical polymerization. Then poly(1-vinylimidazole) grafted polysulfone membrane with different length of side chains is obtained and soaked in phosphoric acid to work as high temperature polymer electrolyte membrane. The tapping-mode AFM images and 1-D SAXS result of PA doped membrane suggest the formation of micro-phase separated structures, and the ionomer peaks shift from 1.34 nm-1 to 1.19 nm-1 with increasing the length of side chain, corresponding to d-spacing of 4.67 nm and 5.28 nm, respectively. Therefore, the prepared phosphoric acid doped membranes possess excellent proton conductivity of 127 mS cm-1 under 160 °C due to the structure, while mechanical properties are retained due to the reduction of plasticizing effect caused by the separation of phosphoric acid adsorption sites and polymer backbone, presenting an outstanding tensile strength of 7.94 MPa. Meanwhile, the impressive fuel cell performance with the membranes is gained, reaching a maximum peak power density of 559 mW cm-2 under 160 oC. More importantly, the work provides a new sight to solve the trade-off between proton conductivity and mechanical strength for phosphoric acid doped high temperature polymer electrolyte membranes. Figure 1

High temperature polymer electrolyte membrane achieved by grafting poly(1-vinylimidazole) on polysulfone for fuel cells application

Phosphoric acid (PA)-doped high temperature polymer electrolyte membranes (HT-PEMs) are crucial materials for HT-PEM fuel cells (HT-PEMFCs). However, the development of HT-PEMs suffers from the trade-off between proton conductivity and mechanical strength. High proton conductivity requires a high doping level of PA, and PA acts as a plasticizer that reduces the mechanical properties. Here, a new strategy is employed to address the unresolved challenges; the strategy is to graft poly(1-vinylimidazole) as PA doping sites on the polysulfone backbone. This is achieved via atom transfer radical polymerization. High proton conductivity is achieved because of the formation of micro-phase separated structures, and the mechanical properties are retained because of the reduced plasticizing effect, which is caused by the separation of PA adsorption sites and the polymer backbone. The prepared PA-doped membranes have excellent proton conductivity of 127 mS cm−1 at 160 °C and outstanding tensile strength of 7.94 MPa. Meanwhile, single H2-O2 cell performance with the optimized membrane is impressive, reaching a peak power density of 559 mW cm−2 at 160 °C. More importantly, this work provides new insight into solving the trade-off between proton transport and mechanical strength for PA-doped HT-PEMs.

Constructing an internally cross-linked structure for polysulfone to improve dimensional stability and alkaline stability of high performance anion exchange membranes

The preparation of quaternary ammonium polysulfone anion exchange membranes (AEMs) with good dimensional stability and alkaline stability is an urgent problem to solve. In response, a series of cross-linked based on polysulfone and 4, 4′-trimethylenedipiperidine (TMDP) as crosslinkers with different degrees AEMs were developed in this work through a simple process. Among the fabricated AEMs, CAPSF-5 exhibits superb alkaline stability in a 1 M KOH aqueous solution at 60 °C for 15 days, whereas the non-crosslinked APSF membrane became tremendously brittle within 24 h and could not be further studied under the same conditions. In addition, even at 60 °C, CAPSF-5 demonstrates a superior dimensional stability compared to the non-crosslinked APSF membrane due to the formation of a dense internal network structure. These observations demonstrate that crosslinked CAPSF membranes can be a viable strategy to improve the deficiency of the polysulfone backbone, especially in terms of alkaline stability.

Polysulfone‐Based Shape Memory Thermoplastics with Body Temperature Triggering

AbstractVarious polysulfone (PSf)‐based shape memory polymers (SMPs) with tunable transition temperature (T trans) are prepared via atom transfer radical polymerization. Hard segments of SMPs are formed by PSf backbone which are then combined with nonlinear derivatives of poly(ethylene glycol) (PEG), that is, poly(ethylene glycol)methyl ether methacrylate as the soft segment. The melting temperature (T m) of soft segments is shown to be an effective stimulus to achieve shape memory behavior. T m values of graft copolymers are found in the range of body temperature from 32.7 to 39.1 °C, and SMPs are obtained with a maximum strain around 464%, tensile strength up to 6.8 MPa, and shape recovery ratio up to 99%. It is shown that the characteristic of SMPs can be tuned by altering the topology and the ratio of soft/hard segments. PSf‐based SMPs can be suitable for various applications since the material’s properties can be tailored for specific applications.

Synthesis and Characterization of Polysulfone-based Graft Copolymer Possessing Quaternary Ammonium Salts via Photoiniferter Polymerization

A well-defined polysulfone-based graft copolymers containing quaternary ammonioum salts are successfully prepared by photoiniferter method under mild conditions. The corresponding macroiniferter agent is sequentially synthesized by chloromethylation and nucleophilic substitution reaction between obtained chloromethylated polysulfone and sodium diethyl dithiocarbamate. Upon UV irradiation, this macroiniferter enables the successful grafting of 2-(dimethylamino)ethyl methacrylate onto the polysulfone backbone in a controlled manner. After the successful synthesis of graft copolymers, the tertiary amine groups in the side-chains are readily quaternized using methyl iodide to get desired quaternary ammonioum salts containing graft copolymers.

Two-dimensional NMR spectroscopy reveals cation-triggered backbone degradation in polysulfone-based anion exchange membranes

Anion exchange membranes (AEMs) find widespread applications as an electrolyte and/or electrode binder in fuel cells, electrodialysis stacks, flow and metal-air batteries, and electrolyzers. AEMs exhibit poor stability in alkaline media; their degradation is induced by the hydroxide ion, a potent nucleophile. We have used 2D NMR techniques to investigate polymer backbone stability (as opposed to cation stability) of the AEM in alkaline media. We report the mechanism behind a peculiar, often-observed phenomenon, wherein a demonstrably stable polysulfone backbone degrades rapidly in alkaline solutions upon derivatization with alkaline stable fixed cation groups. Using COSY and heteronuclear multiple quantum correlation spectroscopy (2D NMR), we unequivocally demonstrate that the added cation group triggers degradation of the polymer backbone in alkaline via quaternary carbon hydrolysis and ether hydrolysis, leading to rapid failure. This finding challenges the existing perception that having a stable cation moiety is sufficient to yield a stable AEM and emphasizes the importance of the often ignored issue of backbone stability.

Polysulfone Functionalized With Phosphonated Poly(pentafluorostyrene) Grafts for Potential Fuel Cell Applications

A multi-step synthetic strategy to polysulfone (PSU) grafted with phosphonated poly(pentafluorostyrene) (PFS) is developed. It involves controlled radical polymerization resulting in alkyne-end functional PFS. The next step is the modification of PSU with a number of azide side groups. The grafting of PFS onto PSU backbone is performed via the "click"-chemistry approach. In a final step, the PFS-grafts are subjected to the post phosphonation. The copolymers are evaluated as membranes for potential fuel cell applications through thermal analyses, water uptake, and conductivity measurements. The proposed synthetic route opens the possibility to tune copolymers' hydrophilic-hydrophobic balance to obtain membranes with an optimal balance between proton conductivity and mechanical properties.

Preparation of a novel phthalimidomethylated polysulfone/unmodified polysulfone blend affinity membrane and applications for removal of p‐nitrophenol

AbstractA novel phthalimidomethyl polysulfone (PIPSf)/polysulfone(PSf) blend affinity membrane was prepared and applied for the removal of p‐nitrophenol from aqueous solutions. In this work, the chloromethylated polysulfone (CMPSf) was used to introduce phthalimido groups onto the polysulfone backbone by Gabriel reaction. The polymers can be easy to phthalimidomethylate to different degrees by control of the reaction temperature and time. Structures of the resulting polymers were confirmed by FT‐IR. The obtained polymers showed good solubility in dimethylformamide, dimethylacetamide and formed the affinity membrane blending with polysulfone at different blend compositions by the phase‐inversion method. Thus the properties of films were characterized with respect to water flux, pore size, and porosity. The surface and cross‐sectional views of the blend membranes were analyzed by scanning electron microscopy (SEM). The research on treatment of removal p‐nitrophenol was carried out by affinity membrane process. The adsorption capacity increased with increasing the initial concentration of p‐nitrophenol in aqueous solution, and the adsorption isotherm fitted the Freundlichmodel well. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Chain scission resists for extreme ultraviolet lithography based on high performance polysulfone-containing polymers

A series of polymers with a comb architecture were prepared where the poly(olefin sulfone) backbone was designed to be highly sensitive to extreme ultraviolet (EUV) radiation, while the well-defined poly(methyl methacrylate) (PMMA) arms were incorporated with the aim of increasing structural stability. It is hypothesized that upon EUV radiation rapid degradation of the polysulfone backbone will occur leaving behind the well-defined PMMA arms. The synthesized polymers were characterised and have had their performance as chain-scission EUV photoresists evaluated. It was found that all materials possess high sensitivity towards degradation by EUV radiation (E0 in the range 4–6 mJ cm−2). Selective degradation of the poly(1-pentene sulfone) backbone relative to the PMMA arms was demonstrated by mass spectrometry headspace analysis during EUV irradiation and by grazing-angle ATR-FTIR. EUV interference patterning has shown that materials are capable of resolving 30 nm 1 : 1 line : space features. The incorporation of PMMA was found to increase the structural integrity of the patterned features. Thus, it has been shown that terpolymer materials possessing a highly sensitive poly(olefin sulfone) backbone and PMMA arms are able to provide a tuneable materials platform for chain scission EUV resists. These materials have the potential to benefit applications that require nanopattering, such as computer chip manufacture and nano-MEMS.

New highly phosphonated polysulfone membranes for PEM fuel cells

This paper reports the development and characterization of phosphonated poly(arylene ether sulfone) polymer electrolytes for direct methanol fuel cells. The synthesis of phosphonated polysulfone was performed by a post-phosphonation method via chloromethylation of the polysulfone backbone followed by phosphonation utilizing the Michaels–Arbuzov reaction. High degree of phosphonation up to 150% was achieved without crosslinking side reactions. The obtained membranes/polymers in the ester form were hydrolyzed to the corresponding phosphonic acid by refluxing in aqueous hydrochloric acid. The modified polymers were characterized by nuclear magnetic resonance, infrared spectroscopy, ion exchange capacity, differential scanning calorimetry and thermal gravity analysis. The high level of phosphonic acid content 150% led to high water uptake level 52 wt% which is necessary to reach high proton conductivity values. The synthesized membranes with the highest phosphonic acid content 150% reached 12 mS/cm at 100 °C under fully hydrated conditions and showed low methanol crossover (9.12 × 10 −8 cm 2/s) compared to Nafion 117 membranes. Also, membranes with 150% phosphonic acid content exhibit high thermal stability up to 252 °C under air which entitle them as future candidates for proton exchange membrane fuel cells PEMFCs.

Polysulfone-based Ionomers for Fuel Cell Applications

This paper is a review that is focused on ionomers based on aromatic polysulfone backbone and intended to be used in proton exchange membrane fuel cells or in direct methanol fuel cells. Emphasis is placed on the different chemical routes to prepare the ionomers. Special attention is given to the impact of the ionomer structure on the conductivity performance and on the dimensional stability of the membranes at high temperatures.

Preparation and characterization of proton conducting polysulfone grafted poly(styrene sulfonic acid) polyelectrolyte membranes

The syntheses of series of proton conducting comb copolymer membrane involving polysulfone back bone as main chain and poly(styrene sulfonic acid) (PSSA) being side chain, i.e. polysulfone grafted poly(styrene sulfonic acid) (PSU-g-PSSA) are presented. Chloromethylation of the polysulfone backbone was done by Fridel Craft alkylation reaction. Atom transfer radical polymerization was used for control grafting from the chloromethylated positions. The successful substitution of the chloromethyl group and its grafting with PSSA was characterized by elemental analysis and proton nuclear magnetic resonance. Water uptake, electrochemical properties like ion exchange capacity (IEC) and proton conductivities increase with increase in PSSA contents. Thermal gravimetric analysis (TGA) showed the thermal stability of membranes up to 250 °C. Proton conductivity for maximum amount of grafting is 0.02 S/cm.

Transport Properties of Hydroxide and Proton Conducting Membranes

Hydroxide anion conducting solid polymer membranes, also termed anion exchange membranes, are becoming important materials for electrochemical technology, and activity in this field, spurred by renewed interest in alkaline fuel cells, is experiencing a resurgence. Solid polymer anion exchange membranes enable alkaline electrochemistry in devices such as fuel cells and electrolyzers and serve as a counterpoint to proton exchange membranes, of which there is a large body of literature. For their seeming importance, the details of transport in alkaline exchange membranes has not been explored thoroughly. In this work, a chloromethylated polymer with a polysulfone backbone was synthesized. 1H NMR spectroscopy was performed to determine the chloromethyl content and its position on the polymer structure. The chloromethylated polymer was solution cast to form clear, creasable films, and subsequent soaking of these films in aqueous trimethylamine gave benzyltrimethylammonium groups. The resulting anion exchange m...