Yun Jin, Chen Lixin, Zhang Xiaofei, Feng Junjun, Liu Linlin
Department of Applied Chemistry, School of Science, Northwestern Polytechnical University, Xi'an 710072, China.
Science and Technology on Combustion, Internal Flow and Thermal-Structure Laboratory, School of Astronautics, Northwestern Polytechnical University, Xi'an 710072, China.
Polymers (Basel). 2016 Feb 24;8(3):35. doi: 10.3390/polym8030035.
In this contribution, high ortho novolac resins modified with phenylboronic acid were synthesized. The thermal stability of novolac resins cured with hexamethylenetetramine (HMTA) and chemical states of B and N via a pyrolysis process were studied. For the cured -novolac modified with phenylboronic acid, the temperature with maximum decomposition rate increased by 43.5 °C, and the char yield increased by 5.3% at 800 °C compared with cured -novolac. Density functional theory (DFT) calculations show the existence of hydrogen bonding between N of HMTA and H of phenol in modified resin. Thus, N could still be found at high temperature and C=N structure could be formed via a pyrolysis process. B₂O₃ was obtained at 400 °C by the cleavage of B⁻O⁻C and B⁻C bonds and it reduces the oxygen loss which may take part in the formation of carbon oxides in the system. The melting B₂O₃ on the surface of the resin will prevent small molecules and carbon oxides from releasing. Moreover, introducing B into the system helps to decrease the interlayer distance and improve graphite structures via a pyrolysis process.
在本研究中，合成了用苯基硼酸改性的高邻位酚醛清漆树脂。研究了用六亚甲基四胺（HMTA）固化的酚醛清漆树脂的热稳定性以及热解过程中硼和氮的化学状态。对于用苯基硼酸改性的固化酚醛清漆，与固化酚醛清漆相比，最大分解速率对应的温度提高了43.5℃，800℃时的残炭率提高了5.3%。密度泛函理论（DFT）计算表明，改性树脂中HMTA的氮与苯酚的氢之间存在氢键。因此，在高温下仍能发现氮，并且通过热解过程可以形成C=N结构。通过B⁻O⁻C键和B⁻C键的断裂在400℃时获得B₂O₃，它减少了可能参与体系中碳氧化物形成的氧损失。树脂表面熔融的B₂O₃将阻止小分子和碳氧化物释放。此外，将硼引入体系有助于通过热解过程减小层间距并改善石墨结构。
