Synthesis and properties of a novel autocatalytic phthalonitrile monomer and its copolymerization with multi‐functional fluorene‐based benzoxazine monomers

A novel autocatalytic phthalonitrile monomer [4,4′‐(((oxy‐bis [4,1‐phenylene]) bis (azanediyl)) bis (methylene)) bis (2‐methoxy‐4,1‐phenylene)) bis (oxy)) diphthalonitrile, OPD] is obtained by nucleophilic substitution of 4‐nitro‐phthalonitrile and bisphenol compound [4,4′‐(((oxy bis [4,1‐phenylene]) bis (azanylylidene)) bis (methanylylidene)) bis (2‐methoxyphenol)]. Bisphenol compound is a reductant with secondary amine groups of Schiff base derived from the reaction of vanillin and 4,4′‐diaminodiphenylether. The OPD monomer has a self‐catalytic polymerizing reaction. OPD monomer has good processability, and the processing window was 130°C. Moreover, OPD polymer [poly(OPD)] shows higher glass‐transition temperature (345°C). The 5% and 10% thermal decomposition temperatures of poly(OPD) and char yield at 800°C are 407, 451°C, and 69%, respectively. To further improve the properties of poly(OPD), the OPD monomer was modified by multi‐functional fluorene‐based benzoxazine monomers (MFFB) due to their excellent reaction activities. The results showed that OPD/MFFB systems had high reaction activities. The similar thermal stabilities between OPD and MFFB can give stable and excellent thermal stability to the poly(OPD/MFFB). Compared with poly(OPD), the Tg values of poly(OPD/MFFB) were significantly increased, and their stiffness values were reduced. The tensile, flexural, and impact properties for poly(OPD/MFFB) were improved significantly. In the paper, we synthesized a novel auto‐catalytic phthalonitrile monomer containing aryl ether moiety and secondary amino group. The polymerization process of the phthalonitrile monomer is an autocatalytic reaction. The phthalonitrile monomer has good processability. The new polymer shows better thermal properties than traditional polyphthalonitrile. The OPD/diethyleneglycolamine‐based benzoxazine copolymer exhibited the best thermal and thermo‐mechanical properties.