Aryl Fluoride Monomers in Nucleophilic Aromatic Substitution Polymerization: Evaluation of Monomer Reactivity by 19F NMR Spectroscopy

Abstract

The reactivity of a number of aryl fluoride monomers used in nucleophilic aromatic substitution polymerization was explored utilizing 19F NMR experiments. NMR is a valuable tool for evaluating the electron-withdrawing effect of substituents present on phenyl rings. When an electron-withdrawing group is present on a phenyl ring, a partial positive charge develops at the ortho and para positions through resonance interactions. While both 13C and 19F NMR were used to probe the electron density at the actual site of nucleophilic reaction, 19F NMR chemical shifts proved to be the most sensitive probe with a chemical shift range spanning 2500 Hz between the most activated monomer examined, difluorodiphenyl sulfone, and nonactivated fluorobenzene. The 19F shifts reflect the reactivity of the individual monomers examined. Taft inductive and resonance parameters were calculated for a series of monomers from 19F data and used to identify activating forces for the monomers. NMR data were compared with calculated net atomic charges. Relative reactivity studies were also performed in order to verify the utility of this fast and convenient NMR probe of monomer reactivity. © 1995, American Chemical Society. All rights reserved.