Catalytic Polymerization of Mono‐Benzoxazine Functionalized Phthalonitrile Resin by Lewis Acids: Mechanism and Properties

ABSTRACT Phthalonitrile resin is known for its excellent thermal, mechanical, and dielectric properties, but the curing inertness restricts its wide application. In this work, a mono‐benzoxazine functionalized phthalonitrile resin (PN‐BZ) was chosen as the object of study; four different Lewis acids (PCl 5 , ZnCl 2 , FeCl 3 and ZrCl 4 ) and HCl were used as catalysts to probe the effects on the curing mechanism and properties. It was found that PCl 5 and HCl showed high curing activity towards PN‐BZ; PCl 5 and HCl could efficiently promote the ring‐opening polymerization of benzoxazine groups and release abundant phenolic hydroxyls and carbocations. The carbocations were conducive to the formation of an arylamine Mannich‐type crosslinking structure, but too many carbocations would remain in the polymer in the form of iminiums. Due to the fact that iminiums are polar and vulnerable, polymers catalyzed by PCl 5 and HCl showed worse thermal stability and higher dielectric constant. By contrast, the metal cations could better stabilize the polymers by complexation with the phthalocyanine structure.