Polypivalolactone grafts on EPDM

Random copolymers of ethylene, propylene, and 1,4‐hexadiene (EPDM) were carboxylated by reaction with thioglycolic acid or with maleic anhydride. Treatment of these polymers in tetrahydrofuran solution with tetrabutylammonium hydroxide generated carboxylate anions, which initiated the graft polymerization of pivalolactone. Conversion and grafting efficiencies approached 100%. Polypivalolactone chains had an estimated DPn of 3 to 20 and the average distance between graft sites varied from 3000 to 7700 molecular weight units. On cooling from the melt, highly crystalline domains of polypivalolactone formed, which melted at 120–200°C depending on DPn. Electron microscopy and x‐ray analysis verified the presence of these domains, which serve as reinforcing tiepoints for thermally reversible network formation. The resultant thermoplastic elastomers have excellent elasticity and strength, and their compression set resistance is equivalent to that of conventionally cured and reinforced EPDM. This paper details the synthesis, morphology, and structure–property relationships of these elastomers.