Photoactive polymers containing vanadium: 1. Preparation, characterization and photoreactions

Abstract

Photoactive polymers have been prepared by reaction of VOQ 2OH (Q = 8-quinolyloxo) with polymers of types A and B carrying pendant hydroxyl groups. Type A was represented by copolymers of methyl methacrylate and 2-hydroxyethyl methacrylate and type B by a copolymer of styrene and p-vinylbenzyl alcohol. The final copolymers are designated VA, VB, respectively. The copolymers were characterized by near u.v.—visible spectra. On irradiation ( λ = 365 nm) the vanadium (IV) chelate VOQ 2 is formed; this is indicated by the u.v.—visible spectral changes, and also by e.s.r. spectroscopy. The infra-red spectra of the copolymers VA, VB show important differences, notably the presence of a strong band near 960 cm −1 (attributable to V=O stretching vibrations) in the former and its absence from the latter. From this and other evidence it is concluded that the vanadium residues have different structures in the two types of copolymer, viz. O=VQ 2OR and (HO) 2VQ 2OR in VA and VB respectively, where R is the remainder of the copolymer molecule. Irradiation ( λ = 365 nm) is considered to bring about scission of VOR bonds in copolymer VA with formation of a macroalkyloxy radical OR. This is consistent with spin-trapping experiments with benzylidene nitrone. On the other hand, photolysis of copolymer VB appears to give radicals identical with those from VOQ 2OH which are most probably OH. The formation of different types of radical on irradiation of copolymers VA, VB is also indicated by spin-trapping observations with nitrosodurene in benzene solution and also the occurrence of photografting when VA (but not VB) is irradiated in a monomer. The photolysis of VOQ 2OH to which we have referred above may provide a convenient source of hydroxyl radicals in non-aqueous solution.