Synthesis and Characterization of Soluble Polyimides Derived from 4,4′‐Diamino‐3,3′‐dimethyldiphenylmethane and Their Pervaporation Performances

Two kinds of soluble polyimides were synthesized from 4,4′‐diamino‐3,3′‐dimethyldiphenylmethane (DMMDA) and two dianhydrides (including BTDA, ODPA) via a two‐step method, low temperature solution polycondensation and next chemical imidization. All polyimides were readily soluble in common polar solvent, such as DMF, DMAc and NMP. The polyimides were characterized by FT‐IR, NMR, DSC, XRD and EA. The results showed that all of the polyimides revealed an amorphous nature and their inherent viscosities were 0.68–0.96 dlg^?1. The glass transition and melt temperature of these polyimides were determined by DSC and ranged from 224–283°C and 372–384°C, respectively. Thermogravimetric analysis indicated that these polyimides remained fairly stable up to a temperature around or below 400°C. Moreover, 10% mass losses were recorded at approximately 525°C in nitrogen atmosphere. They had a tensile strength in the range 89–137 MPa, and elongations breaking at around 10%. The pervaporation properties of the prepared polyimide dense membranes for ethanol/water mixtures were investigated at a different temperature and the average value of the separation factor and total permeation flux were 46–108 and 660–1380 g/m²h, respectively.