Synthesis, characterization, and structure-property relationships of aromatic polyimides containing 4,4′-diaminotriphenylmethane

This work reports two series of structurally different aromatic polyimides based on 4,4'-diaminodiphenylmethane (DPM) and 4,4'-diaminotriphenylmethane (TPM) and three commercial dianhydrides. All TPM-based polyimides formed membranes due to their high molecular weight (inherent viscosities similar to 0.93-1.14 dl/g), they exhibited high thermal stability (5 %: 490-544 degrees C), glass transition temperatures between 269 and 293 degrees C, and reasonable mechanical properties. The incorporation of pendant phenyl moieties in the TPM-based polyimides has a strong effect producing an improvement in solubility, thermal stability, density and gas permeability coefficient in comparison with DPM-based polyimides. The most interesting polyimide TPM-6FDA, containing phenyl and trifluoromethyl as bulky pendant groups, showed higher gas permeability coefficient for CO2 (23.73 Barrer) and the best ideal selectivity to the gas pair CO2/CH4 (alpha = 28.93).