摘要
Self-cross-linkable main-chain polybenzoxazines (PBz) could be directly obtained with polymerization of a diamine, a bisphenol compound, and formaldehyde. Two major concerns of preparation of main-chain PBz are gelation in the polymerization system and low molecular weight of the PBz products. In this work, an effective approach to address the issues has been demonstrated with employing a Meldrum's acid-containing diamine (MADA) as a functional monomer. MADA could retard the trimerization of methylol groups and formation of cyclic triazines in the polymerization system through the interaction between MA and methylol groups, so as to prevent gelation occurring in the polymerization system. With the self-protection of the diamine monomers, adjustments of the used solvents have been done to prevent PBz precipitation from the polymerization solution in the duration of reaction and consequently to result in an increase in the molecular weights of the prepared PBz (MW: 12500 Da; inherent viscosity: 0.39 dL g-1). Moreover, the MA groups provide additional cross-linking sites to the PBz chains, so as to increase the cross-linking density and enhance the thermal and mechanical properties of the corresponding cross-linked PBz. The MADA-based cross-linked PBz shows good film formability, film flexibility with a near-180° bending, a high glass transition temperature (350 °C), and a Young's modulus of 2.26 GPa. The values are superior over the data (Tg: 267 °C; Young's modulus: 1.74 GPa) found with the conventional 4,4′-oxydianiline-based cross-linked PBz. Significant advances on both PBz synthesis and cross-linked PBz properties have been demonstrated.