To ameliorate the trade-off effect between ionic conductivity and water swelling of anion exchange membranes (AEMs), a crosslinked, hyperbranched membrane (C-HBM) combining the advantages of densely functionalization architecture and crosslinking structure was fabricated by the quaternization of the hyperbranched poly(4-vinylbenzyl chloride) (HB-PVBC) with a multiamine oligomer poly(N,N-Dimethylbenzylamine). The membrane displayed well-developed microphase separation morphology, as confirmed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Moreover, the corresponding high ionic conductivity, strongly depressed water swelling, high thermal stability, and acceptable alkaline stability were achieved. Of special note is the much higher ratio of hydroxide conductivity to water swelling (33.0) than that of most published side-chain type, block, and densely functionalized AEMs, implying its higher potential for application in fuel cells.

It is important to emphasize that the adjustment of an organic–inorganic interfacial chemical environment plays an important role during the separation performance of composite materials. In this paper, a series of hybrid membranes were prepared by blending polyvinyl alcohol (PVA) solution and sulfonated nano-TiO₂ (SNT) suspension. The effects of different interfacial chemical surroundings on ions transfer were explored by regulating the dosage content of SNT. The as-prepared membranes exhibited high thermal and mechanical stability, with initial decomposition temperatures of 220–253 °C, tensile strengths of 31.5–53.4 MPa, and elongations at break of 74.5–146.0%. The membranes possessed moderate water uptake (WR) values of 90.9–101.7% and acceptable alkali resistances (swelling degrees were 187.2–206.5% and weight losses were 10.0–20.8%). The as-prepared membranes were used for the alkali recovery of a NaOH/Na₂WO₄ system via the diffusion dialysis process successfully. The results showed that the dialysis coefficients of OH⁻ (U_OH) were in a range of 0.013–0.022 m/h, and separate factors (S) were in an acceptable range of 22–33. Sulfonic groups in the interfacial regions and –OH in the PVA main chains were both deemed to play corporate roles during the transport of Na⁺ and OH⁻.

Polyolefin-based anion exchange membranes have recently been increasingly studied, but obtaining polyolefins with controllable molecular weights and high chemical stability under facile and metal-free conditions remains a critical challenge. Here, we demonstrate a novel strategy of exploiting visible light-induced reversible addition–fragmentation chain transfer polymerization (Vis-RAFT) for the preparation of poly(2-chloroethyl vinyl ether) (PCEVE), which exhibits high alkaline stability. With this strategy, we can control the molecular weight of PCEVE by an “on/off” light procedure. The quaternization of PCEVE yields quaternized poly(2-chloroethyl vinyl ether) (PQEVE) membranes with a well-defined microphase-separated morphology, a high chloride conductivity of 26.1 mS cm⁻¹ at 30 °C, and a significantly reduced water swelling of 1.2% at 80 °C. We anticipate that this strategy can be a potent alternative to metal-catalysed coordination polymerization or metathesis polymerization in preparing high molecular weight polyolefins for membrane applications.

Carboxyl-type boronic acid copolymers (CBACs) were synthesized by a radical polymerization method and used for the preparation of polyvinyl alcohol (PVA)-based composite membranes via a solution mixture method. The as-prepared composite membranes exhibited a water uptake (W_R) of 122.6–150.0%, an ion exchange capacity (IEC) of 0.0147–0.0518 mmol g⁻¹, and excellent mechanical (elongation at break (E_b) of 103.8–148.4%, tensile strength (TS) of 38.7–58.6 MPa) and thermal stability. The alkali resistances of the as-prepared membranes were tested by immersing the samples into 2 mol L⁻¹ NaOH solutions at 25 °C for 60 h, and the results were encouraging: the mass loss and swelling degree of the as-prepared membranes were in the ranges of 1.9–5.9% and 222.6–241.9%, respectively. The separation performances of the as-prepared membranes were evaluated by the diffusion dialysis (DD) process with an NaOH/Na₂WO₄ mixture at room temperature. The results demonstrated that the dialysis coefficients of hydroxide (U_OH) were in the range of 0.0147–0.0347 m h⁻¹, and the separation factors (S) were in the range of 29.5–62.6. The introduced carboxyl groups from CBACs and the –OH groups from PVA were both deemed to play significant roles in the promotion of ion transport: the –COO⁻ groups formed negatively charged transport channels for Na⁺ by electrostatic attraction, and the –OH groups promoted the transport of OH⁻ via hydrogen bonding.