For applications in ultrafiltration membranes, cancer cell uptake, bioimaging, and diagnostics, a reverse dissolution approach, where swollen poly(vinyl alcohol) (PVA) particles are added to a butyraldehyde solution in ethanol, is employed to synthesize poly(vinyl butyral) (PVB) with high contents of butyral groups. The final butyral group content (up to 84%) of PVB is found to be dependent strongly on the initial condensed state of PVA, the degree of polymerization of PVA, the purity and volume of ethanol, and the pH value. A maximum of butyral group content may be obtained under conditions: swollen PVA particles, (95 vol %) ethanol of 125–150 mL, and pH 1. This reverse dissolution approach has advantages such as a mild reaction condition (70 °C), no predissolution of PVA at high temperatures, no vacuum removal of water during reaction, and low water consumption in post-treatment of the product.

A single-sheet bipolar membrane was synthesized via photografting polymerization of an acrylic acid cation exchange layer onto the surface of a commercial homogeneous anion exchange membrane with benzophenone (BP) as the main initiator, diphenyl (2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) and 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173) as coinitiators and divinylbenzene (DVB) or neopentylene glycol diacrylate (NPGDA) as crosslinking agent. It was found that when benzophenone was used as single initiator and the crosslink agent is absent, the grafting degree (Dg) increases with the prolongation of irradiation time. The grafting degree reaches a maximum at 60 seconds reaction time when the crosslinking agent is added, and the grafting degree is higher when using NPGDA instead of DVB as crosslinking agent. The grafting degree increases as the composite initiator system is used. When polymerization was initiated by BP and TPO, and the dosage of NPGDA was 2.5% mol concentration of monomer, the grafting degree reaches 30.1%.

A pH-switching membrane with novel pore-covering structure was designed and synthesized by photografting 4-vinylpyridine (4VP) onto the poly(ethylene terephthalate) (PET) track membranes. The membrane has a thin grafting layer, which was confined to the membrane surface rather than inside pores. The ATR-FTIR and atomic force microscopy (AFM) were used to characterize the photografting polymerization and the configuration of membrane pores in different conditions. The membrane pores are regulated by the grafted poly(4-vinylpyridine) chains, which give a pore-covering effect by stretching over or into the pores. The water fluxes of the grafted membranes have great leap near the pH range of 2–4 even with a very low grafting degree (0.3 wt%). Moreover, the fluxes approximate to that of blank membrane in neutral solution (open state), and close to zero in acidic solution (close state). Different from poly(acrylic acid) grafted membranes, the poor water solubility of poly(4-vinylpyridine) makes the grafting chains float on the surface of water inside pores and no obvious open and close configuration of the membrane pores were observed under AFM. The filtration test indicated that grafted membranes have no retention to both riboflavin and bovine serum albumin (BSA) under pressure driving, whereas diffusion tests showed that both in open and close states, the BSA could be trapped completely at high grafting degree (more than 2.54%) while riboflavin can freely diffuse through the membranes.