An investigation of the structure of furfuryl alcohol polycondensates with infrared spectroscopy

Furan resins were prepared by the polymerization of furfuryl alcohol with either acid or thermal catalysis. The effect of catalysts, solvents, polymerization time, and atmosphere were studied for their effects upon the chemical structure of the polymer produced. It has been found that, regardless of the technique employed, the resins contained appreciable amounts of ketonic species. Examination of the infrared spectrum of these resins indicated that the relative amount of ketonic material to furan ring–containing species was the same, regardless of the resin viscosity. It is proposed that the ketonic species arise during the polymerization by ring–opening of the furan unit, forming γ‐diketone functional systems as part of the polymer unit. The resins were separated into crude fractions by vacuum distillation, base extraction, and fractional precipitation. From heat‐catalyzed resins a lactonic component identified as 5‐hydroxy‐3‐pentenoic γ‐lactone was isolated. The curing of furan resins in nitrogen was shown to proceed through further condensation of furan methylol groups with furan rings having an available α‐hydrogen. β‐Hydrogen crosslinking reactions were not supported by infrared examination of the curing process.