Copolymerization of phthalonitrile-based resin containing benzoxazine and cyanate ester: Curing behaviors, fiber-reinforced composite laminates and improved properties

Curing behaviors and copolymerization mechanisms between phthalonitrile-based resin containing benzoxazine (A-ph) and cyanate ester (CE) were characterized and discussed. Results indicated that copolymerization between A-ph and CE were comprised of ring-opening polymerization of oxazine rings and ring-forming polymerization of cyanate and nitrite groups. From them, ring-opening of oxazine occurred preferentially, followed by ring-forming of cyanate and nitrile groups, which were promoted by active hydrogen and amine structures generated from ring-opening of oxazine. Moreover, with increasing the content of CE (>= 40 wt%), self-polymerization of cyanate would dominate the components of the resulting composites and reduces the thermal stability of fiber-reinforced composite laminates. Additionally, mechanical properties of composite laminates were also affected by the content of CE. Composite laminates with 10 wt% CE showed the highest flexural strength (622 MPa). The improved mechanical properties were also verified with investigation of dynamic thermomechanical analysis and morphology of fracture surfaces. These findings are helpful to improve the thermosetting resins in terns of their chemical structure, material properties, and processability.