A novel catalyst for the cure of carboxy‐terminated polybutadienes

The catalysis of the reaction between carboxylic acids and epoxides was examined in general and with special reference to the cure of carboxy‐terminated polybutadienes. It was established that the most active catalysts were the chromium chelates of salicylic acid or substituted salicylic acids. 3,5‐Diiso‐propylsalicylato chelates were studied in detail because of their solubility advantages. Reaction mechanisms are proposed which are in agreement with the kinetic data. A variety of applications were established for the new chelate catalyst. They include: synthesis of hydroxyalkyl carboxylic acids; efficient low‐temperature cure of liquid rubbers with possible regulation of chain extension and crosslinking; and use of the catalytic system for room‐temperature‐cured, midly acid adhesives of high strength and rubber‐modified epoxy resins.