Synthesis and characterization of random and block copolymers with pendant rhenium diimine complexes by controlled radical polymerization

Abstract

We report the polymerization of rhenium-containing methacrylates by atom transfer radical polymerization. The structure of the monomer was confirmed by X-ray crystallography, which showed the bulkiness of the metal-complex moiety. The rhenium complexes were polymerized in the presence of copper(I) bromide, 1,1,4,7,7-pentamethyl-diethylenetriamine, and methyl 2-bromopropionate. They were copolymerized with methyl methacrylate in different monomer ratios. An ABA triblock copolymer was also synthesized with poly(methyl methacrylate) as the macroinitiator. When 2,2'-bipyridine was used as the ligand for the copper catalyst in the polymerizations, it underwent a ligand exchange process with the iminopyridine ligand in the monomer. The neutral rhenium complex in the homopolymers and copolymers could be converted into ionic forms by the replacement of the chloride with an imidazole ligand, and the solubility of the resulting ionic polymers was greatly enhanced. The photosensitizing properties of the doped and undoped polymer films were investigated by the measurement of the photocurrent response under an externally applied electric field. The photoconductivities of the polymers were approximately 10 -12-10 13 Ω 1 cm -1. The experimental quantum efficiencies were simulated with On-sager's theory, and they showed that the initial quantum yield and thermalization distance were 10 -3 and 1.7 nm, respectively. Transmission electron microscopy showed that the rhenium complexes aggregated to form domains with dimensions of approximately 20-30 nm. © 2005 Wiley Periodicals, Inc.