Fourier transform infrared and high-resolution solid-state carbon-13 NMR spectroscopic characterization of cured polystyrylpyridine resins

Abstract

Interesting crosslinked materials possessing good mechanical and thermal properties are obtained by condensation of 2,4,6-trimethylpyridine (collidine) with terephthalic aldehyde in the presence of an acidic catalyst. Fourier transform infrared spectroscopy has been used to follow the kinetics of the chemical reactions involved in the formation of the tridimensional network using aldehyde and ethylene absorption bands. The first steps of the reaction consist in the addition of aldehyde groups on the methyl groups of collidine followed by a dehydration reaction which leads to the formation of ethylenic functions. Crosslinking is obtained by an addition reaction of the methyl groups of collidine on the double bonds created in the first processes. These reactions are strongly dependent on the reaction temperature. Cured resins prepared with different acidic catalysts have been studied by carbon-13 NMR. p-Toluene sulfonic acid leads to residual aldehyde groups in the cured resins whereas no residual aldehyde groups are observed after a relatively short curing time when sulfuric acid is used as the catalyst. The networks created in the two cases are not equivalent and present different mechanical properties.