Synthesis of phosphaphenanthrene-functional monobenzoxazine for enhancing thermal properties of polybenzoxazine thermosets

A facile approach to incorporate an intramolecular 6-membered ring hydrogen bond into a benzoxazine monomer containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) moiety has been developed, leading to a novel monobenzoxazine, ODOPB-pa. This monobenzoxazine was successfully synthesized via a Mannich condensation from 2-(6-oxido-6H-dibenz-[c,e][1,2]oxaphosphorin-1,4-dihydroxy phenylene (ODOPB), propargylamine and paraformaldehyde. The newly obtained ODOPB-pa possesses a relatively lower polymerization temperature than most commercialized benzoxazine resins. In addition, the intramolecular 6membered ring hydrogen bond is identified as an essential feature in its polymerization behavior. The cured product, poly(ODOPB-pa), exhibits high thermal stability with a 5% weight loss temperature of 327 degrees C, and good flame retardant properties with a heat release capacity value of 119 Jg- 1 K-1 and a total heat release value of 41 kJg- 1. Moreover, ODOPB-pa was also applied to mix in different amounts (5, 10, 15 and 20 wt%) with a tri-functional benzoxazine bearing propargyl group, TH-pa. Notably, it has been demonstrated that the TH-pa/ ODOPB-pa blend derived thermoset with 10 wt% ODOPB-pa exhibits the best thermal and flame retardant properties in consideration of the high glass transition temperature (312 degrees C) and very low heat release capacity value (56.5 Jg- 1 K-1). These combined advantages highlight the potential of intramolecular 6-membered ring hydrogen bond-containing ODOPB-based benzoxazine in the producing of high-performance thermosetting systems.

Automated summary

A novel monobenzoxazine, ODOPB-pa, was synthesized by incorporating an intramolecular 6-membered ring hydrogen bond into a benzoxazine monomer. ODOPB-pa exhibited a relatively lower polymerization temperature and the intramolecular hydrogen bond played a significant role in its polymerization behavior. The cured product, poly(ODOPB-pa), demonstrated high thermal stability and good flame retardant properties. The blend of TH-pa and ODOPB-pa showed the best thermal and flame retardant properties when containing 10 wt% ODOPB-pa.