Co‐condensates of resorcinols and methylol compounds for adhesive resins

Abstract

A proton magnetic nuclear resonance study was performed on co‐condensation reactions of resorcinol, 5‐methylresorcinol and 2,5‐dimethylresorcinol with methylol compounds, including ortho‐ and para‐methylolphenol, N‐methylol‐caprolactam, methylol‐N,N‐diethylurea, methylolurea and N,N′‐dimethylolurea. Spectral assignments, reaction kinetics and composition of products are discussed. The reaction in melt (120°C) with methylolphenols occurs as co‐condensation in the presence of all catalysts studied. In resorcinols C4C6 substitution is favored. The rate constants of methylol disappearance clearly indicate the preferable influence of acid and alkaline catalyst (not zinc acetate) on para‐methylol. The reaction with N‐containing methylol compound does not give any co‐condensate in the presence of alkaline catalyst. The optimum conditions for co‐condensation mainly depend on reactivity of co‐reagents with formaldehyde and stability of methylol compound. The quantitative amount of co‐condensate with methylolcaprolactam can be obtained in melt‐condensation (70°C) in the presence of acid catalyst. Because of the higher reactivity of urea, the reaction in melt (100°C) in the presence of acid catalyst does not lead to quantitative co‐condensation. The condensation of methylol compound or resorcinols with formaldehyde can be avoided substantially by performing the reaction in aqueous solution at lower temperature.

Structure of polycondensates from hydroxymethylphenols

“…These resins with predominant content of dihydroxydiphenylmethanes are soluble in pyridine‐d 5 . This was the best solvent for 1 H NMR study of condensation rate of o ‐HMP and p ‐HMP 10. The difference in 1 H chemical shifts for ortho and para HM groups in pyridine‐d 5 is greatest among the various solvents (5.16 and 4.81 ppm, respectively).…”

“…The difference in 1 H chemical shifts for ortho and para HM groups in pyridine‐d 5 is greatest among the various solvents (5.16 and 4.81 ppm, respectively). Because of good resolution of different signals, the study of cocondensation of o ‐HMP/ p ‐HMP was also successful 11. At the same time, 1 H NMR was not applicable for the final assignment of clearly resolved signals at 5.31 and 4.92 ppm in o ‐HMP and p ‐HMP condensation, respectively.…”

Melamine‐bridged alkyl resorcinol modified urea–formaldehyde resin for bonding hardwood plywood

“…2 With their comparatively low price and high reactivity with formaldehyde, AR compounds have been extensively investigated as replacements for costlier resorcinols in the development of cold-setting structural wood adhesives. 3,4 Although the high reactivity is considered a desired property in resin applications, it has also created problems with controlling the reaction of formaldehyde addition in resin synthesis and also with pot life and the storage of the resins. 5,6 To control the excessive reactivity of AR in resin preparation, acetone or other carbonyl compounds have often been added to form hydrogen-bonded complexes with phenolic hydroxyls to reduce the reaction rate of hydroxymethylation.…”

“…3,4 Although the high reactivity is considered a desired property in resin applications, it has also created problems with controlling the reaction of formaldehyde addition in resin synthesis and also with pot life and the storage of the resins. 5,6 To control the excessive reactivity of AR in resin preparation, acetone or other carbonyl compounds have often been added to form hydrogen-bonded complexes with phenolic hydroxyls to reduce the reaction rate of hydroxymethylation. 7,8 Nevertheless, even with complexing agents to reduce reactivity by a factor of 10, the hydroxlymethylation of AR is still eight times faster than the rate of resorcinol.…”

“…5,6 To control the excessive reactivity of AR in resin preparation, acetone or other carbonyl compounds have often been added to form hydrogen-bonded complexes with phenolic hydroxyls to reduce the reaction rate of hydroxymethylation. 7,8 Nevertheless, even with complexing agents to reduce reactivity by a factor of 10, the hydroxlymethylation of AR is still eight times faster than the rate of resorcinol. 9 One study 10 showed that the acetone addition of up to 20 wt % of AR compounds was needed in the resin formulation to achieve the optimum reaction and performance of an AR resin.…”