The “solid-state” ring-opening cationic polymerization of 1,3,5-trioxane: frozen polymerization for suppression of oligomer formation and synthesis of ultrahigh molecular weight polymers

Abstract

The production of polyoxymethylene (POM) with higher molecular weights and lower oligomer ratios than those obtained by molten-state polymerization of 1,3,5-trioxane (TOX) was demonstrated by lowering the temperature during the polymerization or by conducting solid-state polymerization at a temperature lower than the melting point of TOX. Side reactions, such as oligomer formation, occur during the polymerization of TOX in a molten state due to the free movement of active chain ends. To suppress the side reactions, we managed the chain end mobility by conducting propagation reactions in the solid state. During “frozen polymerization”, the reaction mixture was cooled to 4, −20, or −78 °C soon after the polymerization started in a molten state. Polymers with a molecular weight M_w of over 1 million were obtained at a final temperature of 4, −20, and −78 °C. During solid-state polymerization, the reaction was started by spraying a catalyst solution onto a solid monomer, which resulted in a polymer containing negligible amounts of oligomers. In both methods, cyclic oligomer formation was suppressed, probably because the active chain end was surrounded by solid-state monomer molecules. In addition, the polymers had an extraordinarily high crystallinity and a fibrous form oriented in one direction.