2-位取代基对聚苯并噁嗪树脂氢键及其性能的影响

Influences of 2-Substituent on Hydrogen Bonds and Properties of Polybenzoxazine Resins

在典型的3-取代苯并噁嗪基础上,在2位分别引入甲基、异丙基和苯基,采用分子动力学模拟研究了2-位取代基对聚苯并噁嗪树脂氢键及其性能的影响。建立了四种聚苯并噁嗪的交联结构,计算了自由体积分数、氢键、玻璃化转变温度T_(g)、热膨胀系数和密度等,结果表明,2-位取代基使聚苯并噁嗪自由体积增加,分子内OH…N螯合氢键比例均有一定程度下降;甲基取代和异丙基取代的聚苯并噁嗪中OH…O氢键的比例提高,而苯基取代的聚苯并噁嗪难以形成OH…O氢键,径向分布函数验证了体系中氢键的形成。空间位阻、自由体积和氢键共同影响了聚苯并噁嗪的玻璃化转变温度和热膨胀系数。2位被苯基取代的聚苯并噁嗪T_(g)最高,为242.0℃,而被异丙基取代的聚苯并噁嗪T_(g)最低,为213.5℃,低于2-位未被取代的聚苯并噁嗪体系。

Based on typical 3-substituted benzoxazines, methyl, isopropyl and phenyl groups were introduced at the 2-position, respectively. Influences of 2-substituent on hydrogen bonds and properties of polybenzoxazine resins were studied by molecular dynamics simulation. Cross-linking structures of the four polybenzoxazines were established, and the free volume fraction, hydrogen bond, glass transition temperature, thermal expansion coefficient and density were calculated. The results show that the 2-substituent increases the free volume of polybenzoxazines and decreases the proportion of OH…N intramolecular chelating hydrogen bonds to a certain extent. The proportion of OH…O hydrogen bonds in methyl-substituted and isopropyl-substituted polybenzoxazines is increased, while phenyl substituted polybenzoxazine is difficult to form OH…O hydrogen bonds. The radial distribution function verifies the formation of hydrogen bonds. Steric hindrance, free volume and hydrogen bond affect the glass transition temperature and thermal expansion coefficient of polybenzoxazines. Polybenzoxazine substituted by the phenyl group at the 2-position has the highest glass transition temperature at 242.0℃, while the glass transition temperature of polybenzoxazine substituted by the isopropyl group is the lowest at 213.5℃, which is lower than that of unsubstituted polybenzoxazine.