Synthesis and characterization of phenolic hydroxyl terminated phenylquinoxaline oligomers

The synthesis of phenylquinoxaline oligomers of predictable molecular weight and with phenolic hydroxyl functional end groups is reported. The synthetic procedure utilizes 4-hydroxybenzil as a substituted monofunctional monomer in a conventional PPQ synthesis to both control molecular weight and introduce the functional end groups. The molecular weights of the oligomers were determined by derivatization of the hydroxyl end groups with 3-(trimethylsilyl)propionyl chloride, followed by ¹H-NMR analysis. Comparison of the integration of the trimethylsilyl resonance to the aromatic resonances allowed calculation of the number average molecular weight. A plot of log(η) vs. log(M_n) correlated well with that reported for high molecular weight PPQ. The end groups influenced the solubility behavior of the oligomers in chlorinated solvents, possibly due to hydrogen bonding. The oligomers were chain-extendable to high molecular weight, confirming their suitability for utilization in copolymerizations to prepare phenylquinoxaline-based block copolymers.