Preparation and characterization of PMR-type polyimides from furan-based diamines

PMR-type polyimide resins were prepared in an analogous manner PMR-15 resin is formulated, using two furan-based diamines. The PMR resins from both furan-based diamines showed well-separated transitions that are well-known for PMR-type polyimides, and their oligoimide prepolymers showed lower softening temperatures and cure onsets than PMR-15, making them suitable for lower temperature processing. The cure kinetics of the prepolymers were followed by FTIR spectroscopy. The glass transition and thermal degradation of the crosslinked polyimides were characterized by DMA and TGA which showed in general these polyimides had lower thermal properties than PMR-15. A study on the effects of prepolymer molecular weight was conducted using DFDA to find the optimal stoichiometric number n for better processability and thermal properties. The study determined the polyimide based on DFDA with n = 1.5 had overall a good balance in properties. Its oligoimide precursor softens at 135°C and the cure onset temperature is 231°C. The polyimide has a glass transition temperature of 296°C. Degradation study by TGA showed the lower decomposition temperatures which limit their application temperature to below 300°C. A 1000-h thermo-oxidative stability experiment at 280°C resulted only 6.8% weight loss for DFDA-PI with n = 1.5, making it suitable for high temperature applications around 280°C.