Thermal stability of 6FDA-(co-)polyimides containing carboxylic acid groups

Different (co-)polyimides with and without carboxylic acid groups have been synthesized, characterized and thin films have been prepared. Aging as well as degradation effects at temperatures up to 380 °C have been investigated in order to determine whether high temperature applications are possible. Thus this work was focused on aromatic fluorinated polyimides and copolyimides derived from 6FDA (4,4′-hexafluoroisopropylidene diphthalic anhydride), 4MPD (2,3,5,6-tetramethyl-1,4-phenylene diamine) and DABA (3,5-diamino benzoic acid), since 6FDA-(co-)polyimides are well known for high stability and superior processability. Aging processes have been analyzed using infrared spectroscopy, density measurements and thermogravimetric analysis. It has been found that up to 380 °C the synthesized materials show minor weight losses and aging effects but remain mechanically stable. On the one hand some properties like colour and solubility changed but on the other hand gas separation characteristics could be improved. In all cases structure and mechanical stability persisted after heat treatment. The analytical results lead to the conclusion that the synthesized materials can be used as high performance polymers in various applications, i.e. hydrogen fuel cell and aerospace applications.