Bifunctional benzoxazines: Synthesis and polymerization of resorcinol based single isomers

Aside from their outstanding properties such as thermal and chemical stability and excellent mechanical performance, benzoxazines suffer from high polymerization temperatures. Isomeric mixtures of bifunctional benzoxazines based on resorcinol proved already to be highly reactive monomers enabling polymerizations at lower temperatures. This contribution describes the polymerization behavior of single benzoxazine isomers and furthermore the influence of different substituents at the aniline moiety on the curing temperature. Single isomers of bifunctional benzoxazines are now accessible in a straightforward one-pot synthesis starting from resorcinol and the appropriate N-phenyl functionalized aniline component. The asymmetric benzoxazine monomers bearing no (R-a: Tpeak = 179 °C) or electron-donating substituents in meta position to N (R-3,5dma: Tpeak = 183 °C) succeed in lowering the polymerization temperature. Additionally, the impact of several initiating systems was studied resulting in a decrease of the polymerization temperature for all studied resorcinol derived benzoxazine isomers (down to 144 °C).