Radial polymellitimides were prepared in two steps from mellitic trianhydride and diamines. In the first step of forming a soluble polyamic acid, homogeneous solution polymerization was carried out in a high polar solvent, such as dimethylformamide or dimethyl acetamide, as well as in a nonpolar solvent of tetrahydrofuran. By the tetrahydrofuran process, it was possible to give simultaneous formation and precipitation of polyamic acid free from the usual tightly bound solvents. The insoluble, thermally stable polymellitimides were formed from the polyamic acids by imidation reaction under heat and vacuum. The comparison of thermal and oxidative stability of polymellitimides was also made by DTA and TGA in air and nitrogen atmosphere. The results of these thermal analyses revealed that polymellitic imide ring was highly stable to thermal and oxidative decomposition, while the thermal stability was greatly affected by the structure of diamine components. Polyimides derived from aromatic diamines were proved to have higher thermal decomposition temperature than that of polyimide from aliphatic diamine. Polyimides with methylene or hexamethylene group in the main chain showed decreased thermal oxidative stability in air, while fully aromatic polyimides or polyimide with ether linkage between aromatic rings showed excellent resistance to thermal and oxidative decomposition.

Mellitic trianhydride와 diamine류로부터 2단계 반응으로써 방사형 Polymellitimide류를 합성하였다. 제 1단계인 가용성 polyamic acid의 생성에서 극성용매인 dimethylformamide및 dimethylacetamide와 비극성 용매인 tetrahydrofuran을 사용한 균일용액 중합반응을 비교 검토하였다. 합성상의 용이성과 생성 polyamic acid에 용매분자의 회합 개입을 배제하는 방법으로서는 tetrahydrofuran법이 특히 유용하였다. Polyamic acid를 감압하에 가열 이미드화하여 불용 내열성인 polymellitimide를 얻었다. 생성 Polymellitimide류의 내열성을 DTA 및 TGA법에 의해 질소 기류중 및 공기중에서 측정하여 diamine 잔기 성분에 따르는 차이점을 비교 검토한 결과 polymellitimide의 imide환의 열 안정성은 매우 높았으며, 방향족 diamine으로부터 유도된 polyimide류는 지방족 diamine으로부터의 것보다 내열성이 우수하였고, 주사슬에 methylene기를 함유하거나 hexamethylene기를 지니는 Polyimide는 산화분해에서 그 열 안정성이 저하되었으며, 방향족핵만으로 연결된 것이거나 방향족핵 간을ether 결합으로 이루어진 Polyimide는 열분해 및 산화분해에 대해 안정성이 대단히 큼을 알았다.