Polyphosphazene Membranes. I. Solid-State Photocrosslinking of Poly(4-Ethylphenoxy) (Phenoxy)Phosphazene.

摘要

Dense films of poly((4-ethylphenoxy) (phenoxy)phosphazene), PEPP, a potentially attractive ion-exchange membrane material, were crosslinked to varying degrees using UV light and a photoinitiator. This polymer contained two kinds of substituents: phenoxy groups to be used for possible functionalization (e.g. , sulfonation) and ethylphenoxy sidechains for photocrosslinking, where hydrogens at the benzylic carbons could be abstracted by a photoinitiator leaving macroradicals that after recombination formed covalent bonds. The polyphosphazene polymer was synthesized, mixed with a photoinitiator, shaped into a thin film by solvent casting, and irradiated with UV light for a specified period of time. Benzophenone, BP, was selected as the photoinitiator because it was miscible with polyphosphazene, had the highest rate of hydrogen abstraction and absorbed UV light of 365 nm wavelength. The half-life of benzophenone in 50 micrometers thick irradiated films was determined to be 20 min. When the BP-PEPP molar ratio was increased from 0 to 0.5 the glass transition temperature increased after irradiation from -8.8 to 53.5 deg C. At the same time the equilibrium swelling in dimethylacetamide, at 25 deg C, decreased from infinity to 0.31. Tensile strength tests of the crosslinked films revealed a nonlinear dependence on BP-PEPP molar ratio. jg p2.