The chemical shifts of methylene carbons in phenol novolac resins by carbon-13 nuclear magnetic resonance

The chemical shifts of methylene carbons in phenol novolac resins by carbon-13 nuclear magnetic resonance (C-13 NMR) and the semi-quantitative analysis of 2, 2'-, 2, 4'- and 4, 4'-methylene linkages were discussed. As standards 2, 2'-, 2, 4'- and 4, 4'-dihydroxydiphenylmethanes(DPM) and homologues of p-cresol novolac resins were used. The experimental parameters were as follows: instrument; JOEL Model MH-100 for proton NMR, Model PS-100 and PFT-100 for C-13 FT-NMR, computer; JEC Model-7E, lock system; internal, reference; tetramethylsilane, pulse repetition; 2 sec, numbers of scan; 20004000, data points; 8192, tube; 8 mm in diameter, solvent; d-pyridine, pulse width; 11 μ sec (45°), temperature; room temperature, sample concentration; about 100 mg/ml.The C-13 NMR chemical shifts of 2, 2'-, 2, 4'- and 4, 4'-DPM were 30.9, 35.6 and 40.6 ppm, respectively. It seemed that the dependence of C-13 NMR chemical shifts on the molecular weight were small, because the C-13 NMR chemical shifts of methylene carbons of the dimer, trimer and tetramer of p-cresol novolac resins were 30.9, 30.7 and 30.6 and 30.9 ppm, respectively. The C-13 NMR signals of methylene carbons of phenol novolac resins were broad and chemical shifts of 2, 2'-, 2, 4'-, and 4, 4'-methylene carbons were 30.531.9, 34.936.3 and 40.141.4 ppm.The relative content of 2, 2'-, 2, 4'-, 4, 4'-methylene linkages in phenol novolac both random and high-ortho resins from the relative ratio of each integrated peak area of methylene carbons can be determined semi-quantitatively.