Poly(ethylene oxide) (PEO) of molecular weight from 200,000 to 2,000,000 was crosslinked by exposure to ultraviolet radiation with a high-pressure 150 W mercury lamp. Photochemical crosslinking of PEO proceeds in the presence of photoinitiators such as benzophenone and acetophenone which act as a hydrogen-abstracting agent. Gel fraction yield exceeds 90%, and the number-average molecular weight between crosslinks determined by equilibrium swelling in chloroform varies from 3,000 to 100,000. The degree of crosslinking can be controlled by changing the irradiation temperature.

Summary: Hydrogels of high‐molecular‐weight poly(ethylene oxide) (PEO) have been obtained in situ by applying a very simple procedure that involves UV cross‐linking of PEO in aqueous solution. The efficiency of the photoactivated cross‐linking of thin layers of PEO in aqueous solution in the presence of (4‐benzoylbenzyl) trimethylammonium chloride as a photoinitiator has been determined at room temperature and in a frozen state (−25 °C). It was found that the efficiency varies with the concentration of PEO solution, the molecular weight of PEO, and especially with the temperature. When the UV cross‐linking was performed in the frozen state, porous hydrogels with very high yield of gel fraction (above 90%) and high cross‐linking density were obtained. After drying the hydrogels, films of 50–150 μm thickness were prepared. The films swell extremely fast in water and act as asymmetric membranes.

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