长链聚酰胺酸的热环化动力学

利用GPC、原位FTIR测定了长链聚酰胺酸PAA(由双酚A二酐与 4 ,4′ 二 (4 胺基苯氧基 )二苯酚制备 )的热环化过程 .结果表明 ,在升温热环化的初始阶段 ,聚合物环化的同时其分子链断裂成酐、胺端基分子链 ,相对数均分子量降低 ,薄膜渐脆 ;随着温度进一步的升高 ,酐、胺端基链又重新链合 ,相对数均分子量回升 ,薄膜重具韧性 ;恒温热环化存在两个明显的阶段 ,初期的快速阶段和后期的慢速阶段 ,表现出动力学中断的现象 .采用两步、一级动力学模型研究热环化并得出相关的动力学参数 (速率常数、活化能、指前因子等 ) .针对恒温热环化 ,建立动力学中断时亚胺化程度与温度的关联式 ,从构象转化与自由体积两个方面对动力学中断现象提出解释 ,并由实验数据得到了该关联式的相关参数

KINETICS OF THERMAL IMIDIZATION FOR LONG-CHAIN POLYAMIC ACID

Thermal imidization of the polyamic acid derived from BPADA and BAPS was investigated mainly by GPC and FTIR equipped with an in-situ hot cell.The non-isothermal imidization was carried out in the temperature range from 100℃ to 300℃ with a multi-step heating program.Resalts indicated an initial dissociation of the amide bonds,producing anhydride and amine end groups,and the reduction in molecular weight and the embrittlement of the film.As the temperature was increased further,the above terminal functional groups recombined to increase the chain length and molecular weight,resulting in the toughness recovery of the film.The isothermal imidization included two steps of different reaction rates,a fast step followed by a slow one.That is to say a kinetic interrupt took place.A two-step first-order kinetics model was applied to the isothermal imidization, and the relevant parameters,such as k,E a and A,were obtained.In addition, as the isothermal imidization was concerned,a new empirical formula was proposed to correlate the degree of imidization at the kinetic interrupt point with the curing temperature,which showed a good agreement with the experimental date. Moreover, the kinetic interrupt was explained based on both the conformation change and the effect of free volume.