Phenolic Resins (II) – Influence of the Chemical Structure of High Molecular Weight Molecules on the Mechanisms of Cross-linking and on the Final Structure of the Resins

The physicochemical characterization of the structures of the oligomers (n < 4) in resols has been carried out by fragmenting monomers in LC/UV/MS and LC/UV/MS/MS. Fragmentation mechanisms are related to the numbers and positions of substituents on the aromatic ring and to the types of oligomer junctions. It was more difficult to determine the structures of phenol hemiacetals and dimer hemiacetals because of the large number of position isomers. The resols were prepared with differing molar ratios R = Formaldehyde/Phenol and catalysts. They were cross-linked using two industrially recommended heat cycles. The progression of resin cross-linking was determined by solid state ¹³C NMR (CP/MAS). The residual percentage of monomers and oligomers at n < 4 was determined in leachates (water and methanol) and characterized by LC/UV/MS. The results for cross-linking advancement were correlated with the various synthesis parameters (ratio R, type of catalyst and heat cycle).