Alternating Block Copolymers Consisting of Oligo(phenylene) and Oligo(ethylene glycol) Units of Defined Length: Synthesis, Thermal Characterization, and Light-Emitting Properties

Abstract

Polymers containing conjugated oligo(phenylene) segments of defined length alternating with solubilizing regions of di- to hexa(ethylene glycol) have been synthesized using a Suzuki coupling protocol. Soluble and characterizable materials with up to four benzene rings linked together have been formed without the inclusion of conjugation-disrupting solubilizing side chains. The polymers were generated with weight-averaged molecular weights as high as 158 000 g/mol as determined by GPC-LS. The thermal and luminescence properties of these materials were studied in order to determine how these properties varied with the lengths of the two types of blocks. While the terphenyl polymers were amorphous, the quaterphenyl polymers exhibited multiple transitions in their DSC thermatograms. Polarized light microscopy and X-ray diffractometry were used to investigate this behavior. All of the polymers fluoresced strongly in the blue region of the visible spectrum with a 40 nm red shift in emission between solution and solid-state spectra. UV-visible and fluorescence studies were performed at different concentrations and in solvent/nonsolvent mixtures in order to study possible causes for this spectral shift, which appears to be due to the presence of ground state aggregates.