Photosynthetic membranes. A model study of the influence of photoinitiated grafting and graft polymerization of 1,6-hexanediol diacrylate and 4-( N-ethyl, N-2-acryloxyethyl)amino-4′-nitro-azobenzene, as co-monomers, onto polypropylene ribbon, on permeation and diffusion coefficients of oxygen and nitrogen

Abstract

Photoinitiated grafting and graft polymerization of 1,6-hexanediol diacrylate ( I) and 4-(N-ethyl,N-2-acryloxyethyl)amino-4′-nitro-azobenzene ( II) as co-monomers with a fixed molar ratio I: II equal to 10, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone ( III) as photoinitiator with a ratio R of its molar concentration of 0.005-0.38 with respect to the sum of molar concentrations of I and II, were studied using a polypropylene ribbon as a model system of a macroporous substrate. By polychromatic irradiation at 45°C with energy inputs of 90 mW cm −2, ultrathin layers of co-polymer, able to function as asymmetric membranes, could thus be obtained. Mean polychromatic quantum yields of grafting and graft polymerization, as a function of R, were also measured. Membrane specimens with constant values of grafted (200±20) and graft polymerized (500±80) molecules of monomer units in co-polymer per unit apparent surface (Å 2) have been subjected to measurements of permeabilities (P) and diffusivities (D) at 25°C for oxygen and nitrogen, as a function of R. Results show that only an optimum R minimizes P and D, and a narrow range of R-values allows a normal membrane behaviour.