Recent Advancements in Polyphenylsulfone Membrane Modification Methods for Separation Applications

Polyphenylsulfone (PPSU) membranes are of fundamental importance for many applications such as water treatment, gas separation, energy, electronics, and biomedicine, due to their low cost, controlled crystallinity, chemical, thermal, and mechanical stability. Numerous research studies have shown that modifying surface properties of PPSU membranes influences their stability and functionality. Therefore, the modification of the PPSU membrane surface is a pressing issue for both research and industrial communities. In this review, various surface modification methods and processes along with their mechanisms and performance are considered starting from 2002. There are three main approaches to the modification of PPSU membranes. The first one is bulk modifications, and it includes functional groups inclusion via sulfonation, amination, and chloromethylation. The second is blending with polymer (for instance, blending nanomaterials and biopolymers). Finally, the third one deals with physical and chemical surface modifications. Obviously, each method has its own limitations and advantages that are outlined below. Generally speaking, modified PPSU membranes demonstrate improved physical and chemical properties and enhanced performance. The advancements in PPSU modification have opened the door for the advance of membrane technology and multiple prospective applications.

Highly sulfonated co-polyimides containing hydrophobic cross-linked networks as proton exchange membranes

The cross-linked highly sulfonated co-polyimides based on novel diamine monomer containing double hydrophobic cross-linkable tetrafluorostyrol side-groups showed improved enhanced dimensional stability and superior proton conductivity.

Highly sulfonated co-polyimides containing cross-linkable hydrophobic tetrafluorostyrol side-groups for proton exchange membranes

Highly sulfonated co-polyimides containing cross-linked hydrophobic side-groups showed improved comprehensive performance.

A novel fuel cell membrane with high efficiency

A novel polymer containing an azo based ionic diol has been successfully fabricated as an electrolyte membrane to yield a good fuel cell performance in the whole range of current density.

Segmented tetrasulfonated copoly(arylene ether sulfone)s: improving proton transport properties by extending the ionic sequence

The morphologies and proton-transport efficiencies of segmented copoly(arylene ether sulfone) ionomers that contain tetrasulfonated sequences are compared with the corresponding copolymers with disulfonated sequences. Tetrasulfonated 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl (sBCPSBP) is synthesized by metalation and sulfination. This new monomer is then used in K(2)CO(3)-mediated polycondensations of mixtures with 4,4'-dichlorodiphenyl sulfone (DCDPS) and 4,4'-dihydroxybiphenyl in dimethyl sulfoxide at 110 °C to prepare segmented copolymers with tetrasulfonated units. The corresponding disulfonated copolymers are prepared by using disulfonated DCDPS instead of sBCPSBP. Small-angle X-ray scattering measurements of the fully aromatic copolymer membranes show ionomer peaks that indicate significantly larger characteristic separation lengths of the tetrasulfonated copolymers compared to those of the corresponding disulfonated copolymers with similar ionic contents. This implies a much more efficient phase separation of the ionic groups in the segmented tetrasulfonated copolymer membranes, especially at low-to-medium ionic contents. The enhanced phase separation has a pronounced positive effect on water uptake characteristics and proton transport properties. Under a reduced relative humidity (RH), the tetrasulfonated copolymer membranes show a significantly higher conductivity than the disulfonated ones, particularly at low-to-medium ionic contents. At an ion-exchange capacity of 1 meq g(-1), the conductivity of the tetrasulfonated copolymer membrane at 30 % RH is higher than that of the disulfonated membrane at 90 % RH. Because of their relative ease of synthesis, segmented copolymers based on well-designed multisulfonated monomers may provide a viable alternative to the more complex sulfonated block and graft copolymers for use as fuel-cell membranes.

Hybrid polymers based on sulfonated polynorbornene with enhanced proton conductivity for direct methanol fuel cells

Sulfonated polynorbornene (SPNB) and 3-aminopropyltriethoxysilane (KH550) hybrid cross-linked proton exchange membranes doped with different weight ratio of phosphotungstic acid (PWA) were prepared by a simple sol-gel process. The cross-linked structures led to low methanol permeability and good stability of the nanocomposites. Incorporation of PWA has significantly improved the proton conductivity of the hybrid membrane due to an extra provided conductive proton-conduction pathway to facilitate proton transportation. In particular, the conductivity of SPNB/KH550/PWA25 reached the maximum of 0.02 S.cm−1 at 80°C under the 100% relative humidity condition, and this value is on the same order of magnitude as that of Nafion117. Furthermore, SPNB /KH550/PWA20 owns the lowest proton transport activation energy (8.39 kJ.mol−1).

Sulfonated poly(ether sulfone ether ketone ketone)/sulfonated poly(ether sulfone) blend membranes with reduced methanol permeability

Proton exchange membranes were prepared by blending sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) with sulfonated poly(ether sulfone) (SPES). The morphology, tensile strength, proton conductivity and methanol permeability of the blend membranes were investigated. The scanning electron microscope and transmission electron microscope observation indicates the good dispersion of the SPES in SPESEKK polymer matrix. The addition of SPES also enhances the tensile strength of the SPESEKK membrane. The blend membrane shows lower methanol diffusivity and higher proton conductivity with comparison to the pure SPESEKK membrane, ascribing to the inhabitation of the player SPES to methanol permeation and facilitation of the increment of sulfonic acid groups to the proton transport. The SPESEKK/SPES 5 : 5 membrane exhibits an appreciable tensile strength of 52.3 MPa and a reduced methanol permeability of 6.6 × 10−7 cm2 s−1. This SPESEKK/SPES composite membrane shows a potential feasibility as a promising electrolyte for direct methanol fuel cells.