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, oHPNI-abcb and oPP-abcb, have been successfully synthesized via Mannich condensation using ortho-imide phenols, 4-aminobenzocy-clobutene 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 oHPNI-abcb while no such mechanism can be observed in oPP-abcb. The polymerization behaviors of oHPNI-abcb and oPP-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 oHPNI-abcb and oPP-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 poly-merization mechanism as traditional 1,3-benzoxazine resins have been proposed for both benzocyclobutene-containing benzoxazines. Moreover, thermal gravimetric analyzer (TGA) and the microscale combustion calo-rimetry (MCC) are used to evaluate the thermal stability and flammability of their corresponding thermosets. Notably, the resulting thermoset derived from oHPNI-abcb shows excellent thermal stability with Td5 of 405 C and Td10 of 448 C, while the thermoset based on oPP-abcb exhibits YC800 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(oPP-abcb) and poly(oHPNI-abcb), respectively, evidencing their great potential application in high-performance fields.

Automated summary

Novel 1,3-benzoxazine monomers with ortho-imide and benzocyclobutene functionalities were synthesized and their chemical structures and polymerization behaviors were studied. Multiple polymerization mechanisms were proposed for these monomers, and the resulting thermosets showed excellent thermal stability and flame retardancy.