A ¹³C NMR study of the methylol derivatives of 2,4′‐ and 4,4′‐dihydroxydiphenylmethanes found in resol phenol–formaldehyde resins

Abstract

A total of 13 of the 16 possible methylol derivatives of 2,4 -and 4,4 -dihydroxydiphenylmethane have been synthesized, isolated, and identified. These compounds are found as intermediates in the cure process of resol phenol-formaldehyde (PF) resins. Analysis of the 13 C NMR spectra (in acetone-d 6 ) of these compounds provided a way to evaluate the seven methylolphenol ring types (methylol derivatives of 2-hydroxyphenyl and 4-hydroxyphenyl rings) found in typical resol PF resins using the ipso carbon region from 150 to 160 ppm. A simple diagnostic test was developed using the chemical shift values of the methylol methylene carbon atoms to identify the presence of intermediates containing either a 2-hydroxyphenyl or a 4-hydroxyphenyl ring. Using these data it is now possible to analyze the major components in extracted prepreg PF resins.

Online monitoring of synthesis and curing of phenol–formaldehyde resol resins by Raman spectroscopy

“…The resin sample (w1 ml) was dissolved in DMSO-d 6 (3 ml) and taken into a 5-mm NMR tube (VWR, 5 mm  178 mm, >400 MHz). The 13 C NMR shifts of the solid and liquid state resins were assigned according to the literature [11,17,18,23,25,26].…”

Novel two‐stage phenol–formaldehyde resol resin synthesis

“…The 13 C-NMR signals and the signal areas of resol resins were identified with the help of the literature. 14,[16][17][18][19][20][21] The alkalinity of the samples affected the ppm range of the phenoxy carbon region. Higher alkalinity shifted the phenoxy area to a lower field.…”

A new prepolymer of resol phenol–formaldehyde resin

“…s3) along with HSQC data (Fig. s4) revealed the presence of: aromatic protons at δ6.96, which are correlated to 13 C NMR resonance of δ126.46 in the HSQC spectrum; oxygenated methylene protons at δ4.50, which are attributed to the methylol (CH 2 OH) group in the phenol ring, such protons have correlation with 13 C NMR resonance of δ59.78 in the HSQC spectrum; methylene protons at δ3.71, which are correlated to 13 C NMR resonance of δ40.98 in the HSQC spectrum, should be attributed to para/para methylene bridges according to literature broad resonances of δ8.34 and δ5.22, are proved be exchangeable protons, by using experiment of the addition of H 2 O into deuterated solvents. …”