How Does the Hydrogen Bonding Interaction Influence the Properties of Polybenzoxazine? An Experimental Study Combined with Computer Simulation

The formation of intra- or intermolecular hydrogen bonding and their influences on polybenzoxazine’s properties were investigated after the model benzoxazine monomers (<i>o</i>-AB-fbz, <i>o</i>-AF-fbz, <i>o</i>-AP-fbz, <i>p</i>-AB-fbz, <i>p</i>-AF-fbz, <i>p</i>-AP-fbz) were synthesized. Because of the different electron-donating abilities of bridging units (benzene, furan and pyridine) in isophthalic acid (IPA), 2,5-furandicarboxylic acid (2,5-FDCA) and 2,6-pyridinedicarboxylic acid (2,6-PDCA), the strength of intramolecular H-bonding involved with the oxygen atom in oxazine ring in <i>o</i>-AB-fbz, <i>o</i>-AF-fbz and <i>o</i>-AP-fbz followed the order of <i>o</i>-AB-fbz > <i>o</i>-AF-fbz > <i>o</i>-AP-fbz, and the strength of the overall H-bonding was arranged as follows: <i>o</i>-AB-fbz < <i>o</i>-AF-fbz < <i>o</i>-AP-fbz. While more intermolecular H-bonding was formed in <i>p</i>-AB-fbz and <i>p</i>-AF-fbz as well as <i>p</i>-AP-fbz. DSC and FT-IR results discovered the relationship between the H-bonding involved with the oxygen atom in oxazine ring and the curing activities of benzoxazines. After curing reaction, the cured systems showed varied glass transition temperature (<i>T</i>_g), and the influence of H-bonding on <i>T</i>_g was revealed by in situ FT-IR analysis. Molecular dynamics (MD) simulation was also applied to investigate the properties of synthesized polybenzoxazines and similar results were obtained. Not only the formation of H-bonding but also their effects on both the curing behaviors of benzoxazine monomers and the thermal properties of cured resins were systematically investigated, which would help us understand polybenzoxazines more deeply and might be a guideline for improving their comprehensive properties only by manipulating the H-bonding