Polybenzimidazole [PBI; poly-2,2'(m-phenylene)-5,5'-bibenzimidazole] is known to have excellent high temperature stability (up to 450 degrees C) and superb H-2/CO2 selectivity compared to most high performance (HP) polymers. New blended thermosets were made with PBI and poly(melamine co-formaldehyde) [PMF] to produce stable thin-films after thermal processing at 220-250 degrees C. PBI film formation is difficult, because of challenging processing techniques. As a result, the film tends to fracture and fissure due to processing aids and stabilizers (salt/acid additives) that are found in PBI solutions above 10 wt%. Therefore, PBI dense thin-films are fragile and prone to fracturing during film processing. The reported PBI-PMF blended thermosets do not have stabilizers, and can be made into dense thin-films. The PBI-PMF films were analyzed using pure and mixed gas permeability measurement techniques. At 250 degrees C, the data show H-2/CO2 gas selectivities greater than 13. Also from the gas permeation data, the energy of activation (Ep) of a mixed gas stream for PBI-PMF shows that hydrogen permeates more easily than the other gases, while the permeabilities for the larger kinetic diameter gases are greatly diminished. In addition, the FTIR spectra show that the PBI-PMF films have changed from parent PBI after thermal processing, and PMF dominates the spectra even in minor percent compositions. Overall, the reported PBI-PMF thermoset films show good stability which can be used for high temperature gas separation. (C) 2016 Elsevier B.V. All rights reserved.