Ultem polyimides

Thermoplastic Condensation Polyimides. These include General Electric s Ultem Resin and Amoco s Todon polyamideimide although the latter is no longer offered as injection moldable pellets, but as compression moldable powder and in solution. Another resin, P-84, originally developed by Upjohn but now made by Lenzing (Austria), is based on benzoquinone dianhydride and aromatic isocyanates. 

Polyetherimides (PEI) are polyimides containing sufficient ether as well as other flexibi-lizing structural units to impart melt processability by conventional techniques, such as injection molding and extrusion. The commercially available PEI (trade name Ultem) is the polymer synthesized by nucleophilic aromatic substitution between 1,3-bis(4-nitrophthalimido) benzene and the disodium salt of bisphenol A (Eq. 2-209) [Clagett, 1986]. This is the same reaction as that used to synthesize polyethersulfones and polyetherketones (Eq. 2-206) except that nitrite ion is displaced instead of halide. Polymerization is carried out at 80-130°C in a polar solvent (NMP, DMAC). It is also possible to synthesize the same polymer by using the diamine-dianhydride reaction. Everything being equal (cost and availability of pure reactants), the nucleophilic substitution reaction is probably the preferred route due to the more moderate reaction conditions. 

Polyimide (PI) caps all other polymers in its temperature range of use (-200 to 260 °C in air short-time even up to 500 °C). Because of its high price, it is used in special cases only, such as space vehicles, nuclear reactors and some electronic parts. Newer developments, related to polyimide, are the polyether imides (e.g. Ultem ), polyester imides and polyamide imides (e.g. Torlon ), all with very good mechanical, thermal and electrical properties and self-extinguishing. 

Substrates used included fiber-reinforced epoxy base polymer [FRP], nylon 66, polytetrafluoroethylene [Teflon], poly(ethylene terephthalate) [PET], phenolic resin, and thermoplastic polyimide [ULTEM, GE]. FRPs were the primary substrates used. Initially, they were cleaned with detergent in an ultrasonic bath followed by rinsing with deionized water and alcohol. For further cleaning, they were treated with oxygen plasma (1.33 seem, 60 W, 5 min) followed by a hydrogen plasma treatment (3 seem, 60 W, 5 min). 

Aromatic polyimides are well recognized to have excellent chemical stability, so they have found applications in extremely harsh and corrosive environments. For example, they are used as insulators in nuclear facilities and as thermal blankets on spacecraft where the materials may be exposed to high-energy radiation in the presence of oxygen. The best known of the commercial polyimides is Kapton, which is marketed by Du Pont. The chemical structure of Kapton is shown in Figure 1, along with that of Ultem, another commercial polyimide marketed by General Electric. 

Radical formation in the polyimides on y-radiolysis under vacuum has been investigated by ESR spectroscopy. At 77 K the radical spectra of the irradiated polyimides are composed principally of two partially overlapping singlets (8,9), one of which decays when the temperature is raised to 200 K. This component has been assigned to anion radicals formed at 77 K by trapping of thermalized electrons in the polymer matrix. The other singlet has been assigned to neutral radicals with the free electron delocalized over several units of the polymer chain. These radicals are thus similar to the radicals formed on UV photolysis. Other minor radical components are also sometimes evident in the spectra, for example in that of Ultem that has been irradiated at 77 K (9). 

Following high-energy radiolysis new chemical structures are formed in a polymer. Kapton and many of the other polyimides have been reported to undergo nett chain scission (77) on radiolysis. On the other hand, Ultem undergoes nett crosslinking (70), with a gel dose above 10 MGy. However, the nature of the crosslinks in Ultem has still not been unequivocally identified. 

I wish to thank Dr John Connell of NASA Langley Research laboratory for providing the samples of all of the polyimides discussed herein except those of Kapton and Ultem. I also wish to thank all of my other coworkers whose names appear with mine in the reference list. 

Figure 5 displays the ITPD curves determined at 90 °C of PEEK, PES, and PPS films [27]. Both sulfur-containing polymer films exhibit a pronounced charge drain-off within the first 180 min and hence cannot be considered as electret materials. PEEK, on the other hand, shows a moderate surface potential decay and maintains around 50% charge after 24 h at 90°C. The charge storage characteristics of commercial polyimides and polyetherimide (Ultem 1000) films at 90 °C are displayed in Fig. 6. Kapton HN (PI) films lose almost the complete surface potential within 24 h, exhibiting a steep decay in the first minutes. Upilex R renders better results, since its potential decay is moderate and after 24 h around 45% of the applied charge...

There is a great diversity of polyimides (PI) having = 180-420°C. Several were blended with PC to improve its stiffness, HDT and strength. PEEPC blends were commercialized in 1992 as Ultem LTX, for injection molding or extrusion. They show higher impact resistance than PEI and higher heat resistance than PC, as well as they retain the stain, chemical resistance, and the hydrolytic stability of PEI. 

The best-known are General Electric Ultem poly (ether imides) these offer heat deflection temperatures of 207 to 221°C and continuous service temperatures of 170 to 180°C. Also popular are Amoco Torlon polyamide-imides, with heat deflection temperatures of 278 to 282°C. More specialized are Ciba-Geigy trimethyl phenyl indane polyimides, with heat deflection temperatures of 232 to 257°C, embrittlement times of >2000 hr at 200°C... 

The phase behavior observed with the PBl/Ultem blends is to be contrasted with the phase separation that was observed in blends of PBI with another polyimide, XU218 from Ciba Geigy (Choe et al. 1991). That system showed phase separation only above 400 °C. The actual phase separation temperamies are determined by the blend composition. Thus, the phase behavior that is observed in PBl/polyimide blends is dependent both on the type of polyimide and the thermal history of the blends. 

Pike, R. A., Pinto, J. P, and Brunett, C. M., Moisture Effects in a Polyetherimide— Ultem, Society of Plastics Engineers, 2d International Conference on Polyimides, Recent Advances in Polyimide Technology, 1985, pp. 92-101. 

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