Photocatalysis and promoted photocatalysis during photocrosslinking of multifunctional acrylates in composite membranes immobilizing titanium dioxide

The photocatalytic activities of semiconductor titanium dioxide (added to a standard titanium dioxide pigment) and five organometallic coordination compounds (containing cobalt(III) and vanadium(V) as central atoms) have been investigated during the photopolymerization and photocrosslinking of acrylic monomers, employed for the preparation of composite membranes by photografting onto a non-woven polyester support. By partly or wholly substituting the 30 wt.% titanium dioxide pigment with a semiconductor grade dioxide, the rate of decrease of unsaturation increases (by more than two orders of magnitude when substitution is complete). A strong photocatalytic activity is also shown by vanadium complexes. The rate of decrease of unsaturation call be fitted to a relaxation spectrum, the width of which depends on the chemical nature of the polymer network. The mean lifetime is a very sensitive measure of the photocatalytic effect. Multifunctional acrylic monomers (butanediol diacrylate, 1,6-hexanediol diacrylate and pentaerythritol triacrylate) are photoinitiated by 1,2-diphenyl-2,2-dimethoxyethanone in the presence of semiconductor and pigment grade titanium dioxide blends by the addition of organometallic coordination compounds as photocatalytic promoters. The results obtained in this investigation are in line with the relaxation model described above (also used successfully in previous studies), which interprets the photochemical reactivity during photocrosslinking in the presence and absence of photocatalytic promoters acting as efficient chain transfer agents. The photoinitiator 1,2-diphenyl-2,2-dimethoxyethanone alone is unable to carry out satisfactory polymerization in the presence of massive amounts of pigment grade titanium dioxide in the absence of semiconductor grade dioxide. The latter enhances strongly the rate of crosslinking, which is further increased by photocatalytic promoters. (C) 1997 Elsevier Science S.A.