13C Nuclear Magnetic Resonance Studies of Phenol‐Formaldehyde Resins and Related Model Compounds 2 ‐ Analysis of Sequence Structure in Resins

The paper reports 13C nuclear magnetic resonance spectra of novolac resins and the variation of the composition of the reaction mixture during the in situ preparation of resin. It is observed that in the initial stages of the reaction ortho substitution occurs; however the hemiacetal rather than the methylol derivative is observed. These methylol substituted intermediates are highly unstable and a better appreciation of the relative rates of structure formation can be obtained from an analysis of the methylene bridge region, para‐para Bridges are the first to appear, the next are the ortho‐para and finally the ortho‐ortho linkages are observed. Analysis of the relative intensities of ortho and para bridge carbon atoms allows identification of the isomeric composition of the final resin. The proportion of each isomer depends on the catalyst used in synthesis of the resin.