双官能度手性和消旋苯并噁嗪的合成及热性能研究

采用无溶剂法合成了新型双酚A和双酚AF(六氟双酚A)基手性和消旋苯并噁嗪单体,利用红外光谱(FTIR)、核磁共振氢谱(1H-NMR)、旋光仪和高效液相色谱(HPLC)对单体结构和性质进行了表征,通过差式扫描量热仪(DSC)和热重分析仪(TGA)对苯并噁嗪的固化行为及聚合物的热性能进行了研究.结果表明,无溶剂法合成苯并噁嗪单体具有反应速度快、产率高、对环境友好等特点;双官能度消旋苯并噁嗪单体由内消旋和外消旋异构体组成,且内消旋苯并噁嗪单体含量高于外消旋;手性和消旋苯并噁嗪单体具有相同的开环聚合行为;由于消旋苯并噁嗪分子的立体构型不同,使得聚苯并噁嗪的自由体积减小,分子链的堆积更加致密,因而消旋聚苯并噁嗪的玻璃化转变温度(Tg)和热稳定性均高于手性聚苯并噁嗪和传统的双酚A-苯胺型聚苯并噁嗪;此外,C—F键具有高的解离能,因而双酚AF基聚苯并噁嗪的热性能显著提高.

SYNTHESIS AND THERMAL PROPERTIES OF DIFUNCTIONAL CHIRAL AND ACHIRAL BENZOXAZINES

Novel chiral and achiral bisphenol A and bisphenol AF based benzoxazine monomers were synthesized from the reaction of bisphenol A(bisphenol AF) with paraformaldehyde and primary amines,including(R)-(+)-α-methylbenzylamine and/or(S)-(-)-α-methylbenzylamine,via solventless method.The chemical structures and properties of the benzoxazine monomers were identified by Fourier transform infrared spectroscopy(FTIR),proton nuclear magnetic resonance(1 H-NMR),polarimeter,and high performance liquid chromatography(HPLC).The curing behavior and thermal properties of benzoxazine monomers and cured polymers were characterized by differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA).The results showed that solventless method provided faster reaction rate,higher yields,and was more environmentally friendly than conventional solvent method.Achiral benzoxazine monomers with double chiral center consisted of four isomers,such as two racemic isomers and two mesomeric isomers.The content of mesomeric isomers was higher than that of racemic isomers.Chiral and achiral benzoxazine monomers underwent the same curing behavior.For achiral polybenzoxazines,the methyl and benzyl chains in racemic and mesomeric structures twined for each other in a disorderly manner to be like a wedge due to the different stereo-configuration of achiral benzoxazine molecules,which resulted in lower free volume and tighter packing of the polymer than those of chiral polybenzoxazines.Consequently,achiral polybenzoxazines showed higher glass transition temperature than that of chiral polybenzoxazines and bisphenol A-aniline based polybenzoxazines.Moreover,C—F bond with high dissociation energy contributed to improvement of thermal properties of the polymer.As a result,the bisphenol AF-based polybenzoxazines displayed higher thermal properties than bisphenol A-based polybenzoxazines.