Molecular Weight Characterization of Resole Phenol—Formaldehyde Resins

Number-average molecular weights and intrinsic viscosities in dimethylformamide (DMF) and 1N sodium hydroxide have been determined for alkali-catalyzed phenol-formaldehyde resins prepared under different reaction conditions. Polyelectrolyte effects found in DMF viscosity measurements were corrected for and found to be a result of sodium ions trapped in the resin during many types of separations of the polymer from its caustic reaction solution. Corrections to vapor pressure osmometry data were made by analytically determining the Na+ present by atomic absorption and specific ion electrode techniques. Number-average molecular weights were found in the range of 1300 to 10,000 for fractionated samples. Comparing the data with the Mark-Houwink curves established for linear acid-catalyzed phenol—formaldehyde (novolak) resins gives some insight into the configurational nature of resole resins in solution. The resole data fall close to but a little above the novolak data, which would indicate that he resole resins are flexible and possibly coiled in the pre-cured reaction stage.