聚苯并双噁唑酰亚胺的热分解动力学研究

采用二步法合成了以2,6-二(对-氨基苯)苯[1,2-d;5,4-d’]二噁唑和1,4-二(3,4-二苯氧基)苯四甲酸二酐(HQDPA)为单体的聚苯并双噁唑酰亚胺.该聚酰亚胺的预聚体聚酰胺酸的黏度为1.70 dL/g,经过热环化后能够生成浅黄色的聚酰亚胺薄膜.通过热重分析法研究了聚苯并双噁唑酰亚胺在N2气氛中的热降解机理.采用Flynn-Wall-Ozawa和Friedman法计算了聚苯并双噁唑酰亚胺热降解表观活化能,分别为356.36kJ/mol和370.54 kJ/mol,平均值为363.45 kJ/mol;反应级数为4.22,指前因子为6.44×1016s-1.采用Coast-Redfern法和Phadnis-Deshpande法研究了聚苯并双噁唑酰亚胺的热降解固相反应机理,认为该聚酰亚胺的热降解机理属于反曲线(A3)机理,是成核和增长模式(Avrami equation 2方程)控制的热降解反应,积分形式为g(X)=[-ln(1-X)]3.

THERMAL DEGRADATION KINETICS OF POLY(BENZOBISOXAZOLE IMIDE)

Polyimide(PI-HQDPA) derived from 2,6-bis(p-aminophenyl)-benzo[1,2-d;5,4-d′]bisoxazole and 1,4-bis(3,4-dicarbosyphenoxy) benzene dianhydride(HQDPA) was synthesized via a conventional two-stage method.The intermediate poly(amic acid) had inherent viscosities of 1.70 dL/g and could be thermally converted into light yellow polyimide film.The thermal degradation of the polyimide was studied by thermogravimetric analysis(TGA) using four different methods in order to determine the actual reaction mechanisms of the decomposition process.The apparent activation energy(E) of the solid-state process was determined using Flynn-Wall-Ozawa and Friedman methods,which do not require the knowledge of the reaction mechanism.And the apparent activation energies were resulted to be 356.36 and 370.54 kJ/mol,respectively.So the average activation energy of the polyimide was 363.45 kJ/mol.The reaction order(n) and pre-exponential factor(A) were determined by Friedman method,and the results were 4.22 and 6.44×1016 s-1,respectively.The activation energies of different mechanism models were determined by Coats-Redfern and Phadnis-Deshpande methods,the most probably results were 370.66 and 367.80 kJ/mol,respectively.Compared with the value obtained from the Ozawa method and Friedman method,the actual reaction mechanism of PI-HQDPA obeyed the nucleation and growth model,and could be described by the Avrami-Erofeev function(A3) with an integral form of g(X)=[-ln(1-X)]3.