Soluble and Transparent Polyimides with High Tg from a New Diamine Containing tert-Butyl and Fluorene Units

A novel diamine monomer 1, 4,4'-(9H-fluorene-9,9-diyl)-bis(2-tert-butylaniline), was synthesized from 9-fluorenone and 2-tert-butylaniline by the condensation reaction. Then it was polymerized with several commercial aromatic dianhydrides, respectively, to produce polyimides (PIs) by the one-pot method. The number-averaged molecular weights of the resulting PIs are in the range of (4.54-8.82) x 10(4) with polydispersity indices from 2.51 to 4.33 by gel permeation chromatography measurement. They are soluble in many organic solvents and can form transparent and tough films by solution-casting. The cut-off wavelengths of UV-vis absorption for the PI films are below 360 nm, which are much lower than that of Kapton film. The light transparency of them is above 90% in the visible light range from 400 to 760 nm. They also display relatively low dielectric constants (from 2.79 to 3.00), low water absorption rates (< 1%), and high tensile strength (> 50 MPa). Their excellent solubility and transparency can be attributed to the incorporation of tert-butyl groups and fluorene units into the rigid backbones of PIs. Simultaneously, they still maintain the high thermal stability (the 5% weight loss temperature in the range from 526 to 539 degrees C in nitrogen) and the high glass transition temperatures (T-g > 340 degrees C). (C) 2015 Wiley Periodicals, Inc.