Phenolic resins .3. Study of the reactivity of the initial monomers towards formaldehyde at constant pH, temperature and catalyst type

We have studied the addition of formaldehyde to the various phenolic monomers present in a phenol-formaldehyde system under conditions of constant temperature, pH and catalyst type. The techniques used, carbon-13 nuclear magnetic resonance and high-performance liquid chromatography, enabled us to show the effect of aromatic ring substitution on the reactivity of sites that can potentially react. We have shown from a mechanistic standpoint that the aromatic carbon in the para position is more reactive towards formaldehyde or a hydroxymethyl group than the aromatic carbon in the oi tho position. Condensation reactions involving the para hydroxymethyl group preferentially lead to the formation of compounds with a para-para methylene bridge. From a kinetic standpoint, we have demonstrated that changes in each monomer as a function of time enable the order of reactivity of these compounds towards formaldehyde to be determined under the conditions of temperature, pH and concentration employed.