Developing biobased benzoxazine resins with excellent processability, thermal stability, flame retardancy and dielectric properties

It is a major challenge to develop biobased thermosetting resins with excellent comprehensive performance. Rational molecular structure design is the key to solve the problem. Two biobased benzoxazine monomers, ST-ac and ST-an, were synthesized from salicylaldehyde, tyramine, paraformaldehyde, 3-ethynylaniline or 2-aminobenzonitrile, respectively. Both monomers exhibited excellent processability. The cured resins, poly(ST-ac) and poly(ST-an), were prepared by ST-ac and ST-an respectively. Both two cured resins exhibit superior heat-resistance, thermal stability, flame retardancy, and dielectric properties. These characteristics are attributed to the synergistic interaction between the flexible ethylidene chain segment and the incorporated rigid structural group. Specifically, the glass transition temperatures of poly(ST-ac) and poly(ST-an) are 375 and 236 ℃, the initial thermal decomposition temperatures are 370 and 369 ℃, the heat release rates are 118.4 and 147.3J/g·K, the total heat release amounts are 11.0 and 14.5 kJ/g, the vertical burning test are both UL-94 V-0 rating, and the dielectric constants at 10 GHz are 2.54 and 2.95, respectively. Among them, the overall performance of poly(ST-ac) surpasses that of poly(ST-an), primarily due to differences in the alkynyl and nitrile group curing reactions. The resin developed in this study demonstrates potential for application in high-frequency and high-speed electronic information materials.