novolac

Novolac is a family of phenol-formaldehyde resins produced by acid-catalyzed condensation of phenol with formaldehyde. These resins have relatively low molecular weights and a high phenolic content, forming linear or lightly branched polymers with ether and methylene bridges between aromatic rings. Unlike resole resins, novolacs do not contain sufficient methylol groups and do not undergo self-curing upon heating.

Production and structure: Synthesis uses phenol-to-formaldehyde ratios near 1:1 and acid catalysts such as sulfuric or phosphoric acid, often with water removal to limit crosslinking. The result is a resin that is thermosetting only after a crosslinking step; novolacs are typically described as ready-to-cure resins that require a hardener to cure.

Curing chemistries: To achieve cure, novolac resins require a curing agent. Typical hardeners include polyfunctional amines, ammonium compounds such as hexamethylenetetramine, or other methylene-bridging systems. In many industrial coatings and laminates, novolac resins are used in combination with glycidyl ether groups to form epoxy novolac resins, which cure under standard epoxy curing conditions.

Applications: Novolac resins are used in high-temperature coatings, electrical laminates, and wood adhesives; they are valued for chemical resistance, weathering stability, and thermal performance. They are also used as binders in molded composites and as components in epoxy formulations for demanding environments.

See also: phenol-formaldehyde resin, resol, epoxy resin, epoxy novolac.