Ternary Fluoro-containing Polyimide Blends and Fluoro-containing Polyimide/Polyester Blends Tai-Shung Chung, 1 * Paul Foley 2 and Michael Jaffe 2 1 Department of Chemical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Republic of Singapore 119260 2 Hoechst Celanese Corporation, Corporate Research and Technology, 86 Morris Avenue, Summit, N.J. 07961, USA ABSTRACT Two ternary miscible fluoro-polyimide blends have been identified. They are 6FDA-3,3'-6F-diamine/6FDA-4,4'- 6F - diamine/BTDA - 4,4' - 6FDA blend and 6FDA - 3,3' - 6F - diamine/6FDA - 4,4' - 6F - diamine/ODPA - PMDA - 4,4'-6F-diamine blend (6FDA is 2,2'-bis(3,4'-dicarboxy- phenyl)hexafluoro propane dianhydride, 6F-diamine is 2,2'-bis(3-aminophenyl) hexafluoro propane). Their mis- cibility probably arises from the fact that their diamine parts have hexafluoro isopropylidene groups, their dianhy- dride parts have similar bond angle, space, rigidity and length. Several 6FDA-polyimides and PCTG 5445 (glycol- modified polycyclohexanedimethanolterephthalate) form- ing miscible blends have also been discovered. These surprising results suggest that hexafluoro-isopropylidene- group containing polyimides are quite intermolecular active and the 1,4-cyclohexane dimethanol component in PCTG 5445 may also offer unique miscibility capability. © 1997 by John Wiley & Sons, Ltd. Polym. Adv. Technol. 8, 537–544 (1997) No. of Figures: 5 No. of Tables: 7 No. of Refs: 30 KEYWORDS: fluoropolyimides; fluoropolyimide blends; polymer blends; PCTG; hexafluoro-isopropylidene-group containing polyimides INTRODUCTION Fluoro-containing aromatic polyimides have received attention in the applications of electronic devices, aerospace composites and air-separation membranes. Some fluoro-containing aromatic poly- imides have a superior inherent thermal stability that is one of the critical requirements for an aerospace composite matrix and electronic packaging [1–6]. Some fluoro-polyimides show much lower dielectric properties than those of conventional engineering resins [7, 8]; as a result, electronic devices made from the former have lower electronic interference during the data transmission than that made from the latter. Recent publications also reveal that hexafluoro- modified polyimides play an important role in the development of modern asymmetric skin type mem- branes for air separation. This is due to that fact that several fluoro-containing aromatic polyimides have impressive separation characteristics, i.e. permeabil- ity and selectivity [8–10]. A variety of these polymers have been synthe- sized by NASA and others as matrices for carbon fiber composites [1–4, 11–12]. Blending these high- performance polyimides with other imides or conventional polymers also has received attention. For example, MacKnight and Karasz and their coworkers [13, 14], Jaffe et al. [15] and Chung and coworkers [16–18] have reviewed and investigated polyimide blends as well as PBI (polybenzimida- zole)/polyimide blends. Some of these polyimides contained fluoro-containing aromatic repeat units. Yokota et al. [19] reported their work on rigid rod polyimide blends. Yoon et al. [20] have analyzed ‘‘molecular composite’’ films made from rigid and flexible polyimides, Liang et al. [21] reported thermal and rheological properties of miscible polyethersul- fone and polyimide blends and Feng et al. investigated polyimide blends [22]. Chung et al. [17] have discovered the general * Correspondence to: Tai-Shung Chung. CCC 1042–7147/97/090537–08 $17.50 Received 22 August 1996 © 1997 by John Wiley & Sons, Ltd. Revised 12 May 1996 Polymers for Advanced Technologies Volume 8, pp. 537–544