Structural Aspects of the Solid-State Polycondensation Reaction in Alkali 4-Halogenomethylbenzoates

Sodium and potassium salts of 4-halogenomethylbenzoic acids undergo a polymerization reaction in the solid state upon heating. The reaction products are the corresponding alkali halide (NaCl, KCl, NaBr, KBr) and poly(4-hydroxymethylbenzoic acid). Solid-state 13C NMR spectroscopy was used to characterize parent compounds and reaction products. Lithium 4chloromethylbenzoate and lithium 4-bromomethylbenzoate do not undergo this reaction, and the underlying structural reasons can be understood on the basis of the crystal structures of these materials, which have been determined directly from synchrotron X-ray powder diffraction data. The sodium and potassium compounds could be obtained only as a microcrystalline mixture of polymorphs, a fact that rendered structure determination impossible.