Abstract
Kinetics of the base-catalyzed self-condensation of 4-hydroxymethylphenol (4-HMP) was investigated for the purpose of clarifying the mechanisms of the phenolic resin curing. In order to determine the order of reaction, the dependence of the initial rate of reaction on the initial concentration of the reactant was closely investigated under a wide range of reaction conditions. It was found that the order of reaction was around 1.3. An analysis revealed that unimolecular- and bimolecular reactions occur simultaneously as the rate-determining steps. This is different from the case of the self-condensation of 2-hydroxymethylphenol (2-HMP) where the order of reaction was found to be 1.0 that means only unimolecular reactions take place as the rate-determining step. The rate of reaction due to the unimolecular process could be explained quantitatively by the rate equation based on a quinone methide intermediate hypothesis. The rate of reaction due to the bimolecular process could be explained quantitatively by the rate equation that assumed the following three types of reactions: reactions occurring (1) between two undissociated 4-HMP molecules, (2) between an undissociated 4-HMP molecule and a dissociated 4-HMP molecule, and (3) between two dissociated 4-HMP molecules. As to the bimolecular reactions, the authors suggest that the SN2 type mechanism in which the negatively charged 2- or 4-position of the phenolate ion attacks the methylol carbon of the other molecule is insufficient to explain the kinetics.
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Higuchi, M., Yoshimatsu, T., Urakawa, T. et al. Kinetics and Mechanisms of the Condensation Reactions of Phenolic Resins II. Base-Catalyzed Self-Condensation of 4-Hydroxymethylphenol. Polym J 33, 799–806 (2001). https://doi.org/10.1295/polymj.33.799
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DOI: https://doi.org/10.1295/polymj.33.799
