Wikipedia
Polyhexahydrotriazine
Polyhexahydrotriazines (PHTs) are polymers of hexahydro-1,3,5-triazines, a class of heterocyclic compounds with the formula (CHNR). They are among the strongest known thermosetting plastics and are stable to solvents at pH > 3, but decompose to the monomers in acidic solutions.