Preparation and Properties of Electrospun Polyimide Ultrafine Fibrous Mats with Excellent Heat-fusibility via Hot-press procedure from Organo-soluble Polyimides Containing Phenolphthalein Units

Electrospun polyimide (PI) ultrafine non-woven fibrous mats (UFMs) with good heat-fusibility via hot press procedure were successfully fabricated. For this purpose, two organo-soluble PI resins were prepared via a two-step chemical imidization procedure from two isomeric oxydiphthalic dianhydrides, including the asymmetrical ODPA (2,3,3′,4′-oxydiphthalic dianhydride, or aODPA) and symmetrical ODPA (4,4′-oxydiphthalic dianhydride, or ODPA) with an aromatic diamine containing phenolphthalein unit in the main chain, 3,3-bis[4-(4-aminophenoxy)phenyl]phthalide (BAPPT), respectively. The derived PI-1 (aODPA-BAPPT) and PI-2 (ODPA-BAPPT) resins showed high numerical average molecular weights (Mn) over 105 g/mol and were easily soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N, N-dimethylacetamide (DMAc). PI-1 and PI-2 UFMs were successfully prepared from the PI solutions in DMAc via the one-step electrospinning procedure. Different rotating speeds of 500–2500 round per minute (rpm) for the cylindrical collector were set to investigate the effects of the fiber morphologies on the properties of the PI UFMs. The derived PI UFMs showed good thermal stability with the glass transition temperatures (Tg) over 280 °C and 5 % weight loss temperatures (T5%) higher than 510 °C in nitrogen. The PI UFMs could be successfully heat-sealed via the hot-press temperature at 320 °C (about 40 °C higher than Tg) for 60s with the pressure of 0.5 MPa.