High-performance highly cross-linked networks based on ortho-imide functional mono-benzoxazines containing benzocyclobutene group

Novel 1,3-benzoxazine monomers with ortho -imide and benzocyclobutene functionalities, o HPNI-abcb and o PP-abcb, have been successfully synthesized via Mannich condensation using ortho -imide phenols, 4-aminobenzocyclobutene and paraformaldehyde as starting materials. The chemical structures of synthesized monomers have been confirmed by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and elemental analysis . The structural characterization indicates the presence of isomerism in o HPNI-abcb while no such mechanism can be observed in o PP-abcb. The polymerization behaviors of o HPNI-abcb and o PP-abcb have also been systematically studied using differential scanning calorimetry analysis (DSC) and in situ FT-IR. DSC thermograms show three and two separated exothermic peaks for o HPNI-abcb and o PP-abcb, respectively. The difference in exotherms clearly indicates different polymerization mechanisms are involved in the polymerization process of each benzoxazine . Combined with the variations of characteristic bands during curing process in FT-IR spectra, differentiated multiple polymerization mechanisms rather than a single polymerization mechanism as traditional 1,3-benzoxazine resins have been proposed for both benzocyclobutene-containing benzoxazines. Moreover, thermal gravimetric analyzer (TGA) and the microscale combustion calorimetry (MCC) are used to evaluate the thermal stability and flammability of their corresponding thermosets . Notably, the resulting thermoset derived from o HPNI-abcb shows excellent thermal stability with T d5 of 405 °C and T d10 of 448 °C, while the thermoset based on o PP-abcb exhibits YC 800 value greater than 60%. Furthermore, both thermosets also possess outstanding flame retardancy in the absence of any antiflammable additives with heat release rate values of 23.5 and 22.1 J/(gK) for poly( o PP-abcb) and poly( o HPNI-abcb), respectively, evidencing their great potential application in high-performance fields.