The catalytic mechanism of benzoxazine to the polymerization of cyanate ester

• Two model compounds, PA and s-PA, were successfully synthesized and purificated.
• There is no phenolic hydroxyl in the final ring-opened structures of s-PA.
• Compared with PA, s-PA also can catalyze the polymerization of BADCy.
• The main catalytic process is caused by the oxygen anion.
• The catalytic effect from the phenolic hydroxyl is a secondary factor.

Two model compounds, 3-Phenyl-3,4-dihydro-2H-1,3-benzoxazine (PA) and 6,8-dimethyl-3-(2,4,6-trimethyl-phenyl)-3,4-dihydro-2H-1,3-benzoxazine (s-PA), were successfully synthesized and purificated. Compared with PA, s-PA also catalyzed the polymerization of BADCy even though there was no phenolic hydroxyl in its final ring-opened structures. It was confirmed that the real mechanism of benzoxazine catalyzing the polymerization of cyanate ester is the nucleophilic addition reaction of the oxygen anion on ring-opened benzoxazine to the positively charged carbon atom on cyano group. The catalytic effect also contains the contribution from the phenolic hydroxyl, but it is a secondary factor.