The development of a rod-coil redox polymer composed of biphenyl esters and poly (4-vinylpyridine)

Abstract

A rod-coil polymer was successfully synthesized to provide a backbone structure from which a redox polymer was produced. The rod was composed of biphenyl esters and the coil was composed of poly (4-vinylpyridine). The coil was produced by anionic polymerization at 0⁰C in a 90/10 (v/v) pyridine/tetrahydrofuran solvent mixture. The initiator used was s-butyllithium. The polymerization was quenched with carbon dioxide to provide carboxylic acid end groups. The coil was made with different degrees of polymerization, from 8 to 30. Each polymerization was verified by analyzing ¹H NMR, ¹³C NMR, size exclusion chromatography (SEC), and FTIR results. SEC determined the molecular weights of the coils by using poly (2-vinyl pyridine) standards. The end groups of the polymers were determined by FTIR analysis. One end group was determined to be a s-butyl group, from the initiator, and the other was determined to be either a hydroxyl group or a carboxylic acid. The hydroxyl group is from termination with water in the solvents. The rod was attached to the coil by room temperature esterification. This reaction involved the carboxylic end group of the coil and the hydroxyl end of 4-hydroxy-4-biphenyl carboxylic acid. To prevent the hydroxyl of the carboxylic end from participating in the reaction, the 4-hydroxy-4-biphenyl carboxylic acid was protected by adding a silyl protecting group to the hydroxyl. Analysis of the FTIR spectrum showed that the rod was successfully attached to the coil. A redox polymer was synthesized by covalently bonding a polypyridyl complex of osmium (II) to the pyridine ring of the coil. Five redox polymers were synthesized in all, utilizing coils with different degrees of polymerization (dp = 8, 10, 15, 25, and 30). Each was characterized by cyclic voltammetry, and was found to exhibit reversible electrochemistry.