Blended Polybenzimidazole Thermosets

High performance (HP) polymers, such as polybenzimidazole (PBI) and polyimides, are at the forefront of high-temperature gas separations (>150°C), and previous studies have shown that HP polymers have excellent gas selectivities at elevated temperatures.  PBI is a polymer of interest, because it has been shown to have exceptional gas selectivities at high temperatures.  However, thin membrane formation of PBI is difficult due to stabilizers (salts/acids) that are used in the polymer solutions. When using these stabilizers, the processed PBI membranes tend to be fragile and prone to fracturing.  To avoid these issues, new PBI blends were synthesized using the parent PBI resin and a co-polymer without these stabilizers.  The resulting films were found to provide excellent thin film membranes after thermal processing, and they show good tolerance towards water.  In addition, the new membranes have excellent gas selectivities at high temperatures and have high free fractional volumes which are not common for HP polymers.  In these studies, the new PBI blend and other HP polymers were compared using gas transport and positron annihilation lifetime analyses.