Polyimides Based on Chloral Derivatives

As can be seen from Table 3.1, polyimides based on 4,4 -diaminobenzophenone and common dianhydrides of tetracarboxylic acids (those of pyromellitic, diphenyloxide-3,3, 4,4 -tetracarboxyhc and benzophenone-3,3, 4,4 -tetracarboxylic acids) possess good thermal properties. However, when in their cyclised forms they are practically insoluble in organic solvents, which restricts the possibility of their investigation, processing and use. 

The synthesis of the poly-(o-chlorophenyl)-imides was accomplished in two steps involving low-temperature reaction between the diamines and bis(phthalic anhydrides) in NMP followed by catalytic imidisation of the PCA directly in the reaction solutions using the catalytic complex pyridine acetic anhydride. The synthesis of polyimides from l,l-dichloro-2,2-di-(3-amino-4-aminophenyl)-ethylene proceeded homogeneously throughout the course of the reaction, as did reactions of 3,3 -diamino-4,4 -dichlorobenzophenone with the dianhydride of diphenyloxide-3,3, 4,4 -tetracarboxylic acid. As to reactions of 3,3 -diamino-4,4 -dichlorobenzophenone with the dianhydrides of pyromellitic and diphenylsulfone-3,3, 4,4 -tetracarboxylic acids, these were homogeneous at the PCA formation step but heterogeneous at the polyimide formation step. Some properties of these polyimides are given in Tables 3.3 and 3.4. 

NMP N-methyl-2-pyrrolidone MC m-cresol TCP, trichloroethane LOI Limiting oxygen index.  

The primary thermal characteristics of the polyimides were determined by dynamic thermogravimetric analysis (TGA) as well as thermomechanically. Although the data for dynamic TGA should be treated with some reservation, one can conclude the following  

The effect of aromatic diamine residues on the heat resistance of polyimides is less clear cut. It was only by comparing thermomechanical curves of polypyromellitimides obtained from 3,3-diamino-4,4 -dichlorodiphenylmethane, and l,l-dichloro-2,2-di(3-amino-4-chlorophenyl)-ethylene that the system containing the 1,1-dichloroethylene group was found to be less heat resistant. With polyimides prepared from other dianhydrides this rule holds true as well but is less distinct. 

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