To discuss the mechanism of ring-opening polymerization (ROP) of benzoxazine, a bisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-0M), o-dimethylbisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-2M), and o-dimethylbisphenol A/o-tetramethyldiaminodiphenylmethane-based polybenzoxazine precursor (PBz-6M) were prepared. Among the polybenzoxazine precursors, free ortho positions to the O of oxazine are available for PBz-0M. No free ortho or para position to the O of oxazine is available for PBz-2M, but free ortho position to the N of oxazine is available. No free ortho positions to the O or N of oxazine are available for PBz-6M. According to DSC, IR, and thermal analysis, we found that the ROP of PBz-2M can be carried out even though no free ortho or para position to the O of oxazine is available. We conclude that the ROP is carried out through the ortho position to the N of oxazine and propose a reaction mechanism to explain the polymerization.

Blends of cyanate ester and benzoxazine have been independently studied by several researchers, and different reaction mechanisms were reported. Recently, we unexpectedly observe that gelation occurred in a 50 wt % methyl ethyl ketone solution of P-oda/BACY (1/1 mol/mol) blend after 24 h at 30 °C, in which P-oda is a 4,4′-oxyaniline/ phenol-based benzoxazine and BACY is a dicyanate ester of bisphenol A. Previous studies suggest that the rapid trimerization of cyanate ester in the blend is related to the ring-opened structure of benzoxazine. However, the possibility of ring-opening polymerization for benzoxazine at 30 °C is rare. Therefore, it is highly likely that the catalytic effect results from the benzoxazine itself, not from the ring-opened structure of benzoxazine. Through IR and DSC analyses, we conclude that the tertiary amine of benzoxazine catalyzes the trimerization of cyanate ester, and we propose a three-step catalytic mechanism of benzoxazine for the trimerization of cyanate ester.

To study the co-reaction of benzoxazine and triazine, a triazine-containing benzoxazine (P-tta) was prepared through nucleophilic substitution of 4-(2H-benzo[e][1,3]oxazin-3(4H)-yl)phenol (P-ap) with 2,4,6-trichloro-1,3,5-triazine.

A polybenzoxazine precursor was prepared via an A–A and B–B condensation, with a much higher molecular weight than those prepared by Mannich condensation. After curing, the thermoset shows robustness in thermal, mechanical, and dielectric properties.

The high performance polyimide, SBC-DDM, exhibits a large free volume, leading to outstanding organo-solubility and a low dielectric constant.