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.

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On irradiation in the presence of Fe(CO),, the allenecarboxylates 1 afforded binuclear carbonyliron complexes 6 (Scheme 3 ) . whereas the allenic lactone 7 under similar conditions gave a mixture of one binuclear and two mononuclear carbonyliron complexes (9,8, and 10; Scheme 4 ) . The structure of the complexes has been elucidated by X-ray crystallography. The structure of the binuclear complex 9 corresponds to that of 6, while 8 has been shown to be a 1,3-butadiene(tricarbonyl)iron complex. The unique structure of 10 represents a new type of allenic complex. A stepwise formation of the complexes via intermediate allene(tetracarbony1)iron complexes of type 11 and 13 is suggested. Treatment of the binuclear complex 6h with FeCI, led to the formation of the free ligand and a mixture of mononuclear complexes 13 and 14 (Scheme 5 ) . On heating, the 1,3-diene complex 8 yielded the free ligand 15, the product of a (1,3) H shift in the allene 7; the complex 10 on the other hand liberates 7 on treatment with ethylenetetracarbonitrile (TCNE) (Scheme 6 ) .