SYNTHESIS OF AND ASSIGNMENT OF C-13 NMR RESONANCES TO M-CRESOL NOVOLAK DIMERS

We have made conclusive assignments of the peaks in the C-13 NMR spectra of five of the six m-cresol novolak dimers (bis(hydroxymethylphenyl)methanes) with the information collected in 2DINADEQUATE NMR experiments. The NMR experiments were carried out on mixtures of isomeric m-cresol novolak dimers, which were prepared by the stepwise condensation of formaldehyde with chloro-m-cresols, followed by hydrogenation. These assignments made possible the measurement of the relative reactivities of the three sites of attack on the ring by formaldehyde in acid-catalyzed condensations. The relative reactivities of the 2-, 4-, and 6-sites of m-cresol are 0.34 +/- 0.06, 0.54 +/- 0.07, and 0.12 +/- 0.06, respectively. Knowledge of these reactivities allows a better understanding of structure of m-cresol novolak resins, which is important in the optimization of photoresists for high-resolution microlithography.