Limiting viscosity number—molecular weight relationships for phenol‐formaldehyde resin in solution

The effect of molecular structure of phenol‐formaldehyde resin on the Mark‐Houwink‐Sakurada equation for solutions in acetone is systematically studied. Random and high‐orthophenol‐formaldehyde resins are prepared by conventional, acid‐catalyzed and Zn++‐catalyzed condensations, respectively. The relative contents of 2,2′‐, 2,4′‐ and 4,4′‐methylene linkages are determined by 13C NMR spectroscopy. From these the detailed distribution of structural isomers is calculated. Several fractions having number‐average molecular weights (by vapor pressure osmometry) M̄n≥104 are isolated by a successive solutional fractionation run from whole random polymers. For solutions of random polymer in acetone at 30°C, [η]=0,631 · M̄ (where [η] is limiting viscosity number) and for high‐ortho polymer [η]=0,0813 · M̄ are established. The former equation can be interpreted in terms of the Zimm‐Stockmayer theory of branched polymer solutions.