Thermoplastic polyimide properties

Recent work has focused on a variety of thermoplastic elastomers and modified thermoplastic polyimides based on the aminopropyl end functionality present in suitably equilibrated polydimethylsiloxanes. Characteristic of these are the urea linked materials described in references 22-25. The chemistry is summarized in Scheme 7. A characteristic stress-strain curve and dynamic mechanical behavior for the urea linked systems in provided in Figures 3 and 4. It was of interest to note that the ultimate properties of the soluble, processible, urea linked copolymers were equivalent to some of the best silica reinforced, chemically crosslinked, silicone rubber... 

Poly[2,2 -(m-phenylene-5,5 -benzimidazole)] (PBI) is a very high glass transition temperature (Tg 430°C), commercially available material. It possesses excellent mechanical properties, but is difficult to process into large parts and has high moisture regain and poor thermo-oxidative stability at temperatures above approximately 260 °C. Polyimides, especially the thermoplastic polyimides, offer attractive thermo-oxidative stability and processibility, but often lack the thermal and mechanical characteristics necessary to perform in applications such as the matrix for high use-temperature (over 300 °C) structural composites (for example, carbon fiber reinforced) for aerospace use. The attempt to mitigate... 

Certain thermoplastic polyimides possess excellent resistances to high temperatures and chemicals, with Tgs ranging from 217 to 371 °C. Certain polyimides also exhibit excellent toughness and dielectric properties. The melt blending process of polyimides with other thermoplastic polymers is difficult due to polyimides high Tg, high melt viscosities, and incompatibility. A solution process is used, therefore, to achieve a semi-interpenetrating polyimide network... 

St. Clair [36] synthesized and evaluated the properties of a semi-2-IPN comprising Thermid 600 (an acetylene terminated imide oligomer from National Starch and Chemical Company) and LaRC-TPI (a thermoplastic polyimide with a Tg of 257 °C). The composition having the ratio of 65 35 of thermosetting Thermid 600 to LaRC-TPI showed the best flexural strength at ambient temperature [36]. 

The cured or fully imidized polyimide, unlike the poly(amic acid), is insoluble and infusible with high thermooxidative stability and good electrical-insulation properties. Thermoplastic polyimides that can be melt processed at high temperatures or cast in solution are now also available. Through an appropriate choice of the aromatic diamine, phenyl or alkyl pendant groups or main-chain aromatic polyether linkages can be introduced into the polymer. The resulting polyimides are soluble in relatively nonpolar solvents. 

Thermoplastic polyimides are available with similar high-temperature and high-performance properties as the thermosets but can be formed using typical melt-processing techniques such as injection moulding. The materials can be used as unfilled base polymer, glass or carbon fibre... 

One of the most successful thermoplastic polyimides has been LARC-TPI, developed by the National Aeronautics and Space Administration (NASA) in the United States. The polymer is commercially available. Table 3 shows some of the very reasonable properties obtained from this adhesive. As indicated, the abihty both to maintain mechanical properties at elevated temperatures and indeed retain mechanical integrity for long periods of time are clearly apparent. 

A partial summary of commercial polyetherimide grade names and their suppliers is listed in Table 8.1. Table 8.2 shows properties of some of the commercial, fully amorphous, melt-processable thermoplastic polyimides listed in Table 8.1. They have high heat capabflity and excellent strength [23]. 

Fig. 33 summarises the typical data discussed in the present section in order to compare the best performing polyimide adhesives at temperatures exceeding 200°C. It can be seen that condensation polyimides (Nolimid 380 and FM 34B ) seem to work better in ageing tests between 260 and 300°C. The thermoplastic polyimides Larc lA and Larc-TPI exhibit excellent adhesive properties between 200 and 232°C, whereas the BMI FM 32 can be used up to 200-230°C. 

M.B. Saeed, Mao-Sheng Zhan (2006) Effects of monomer structure and imidization degree on mechanical properties and viscoelastic behavior of thermoplastic polyimide films. European Polymer Journal. 42 1844-1854. 

Thermoplastic polyimides are linear polymers noted for their high-temperature properties. Polyimides are prepared by condensation polymerization of pyromellitic anhydrides and... 

Engineering thermoplastics are a class of thermoplastic materials that have exceptionally high temperature and chemical resistance. They have properties very similar to those of thermoset plastics and metals. As a result, they are not as easy to weld thermally or to solvent cement as are tbe more conventional thermoplastics. Typical engineering thermoplastics are polysulfone, acetal, amide-imide, and thermoplastic polyimide. 

Morita A. Thermoplastic polyimide. In Margolis J, editor. Engineering plastics handbook thermoplastics, properties, and applications. New York McGraw-Hill 2006. p. 221-38. Chapter 10. 

Fully imidized aromatic thermoplastic polyimides (TPI) are linear polymers with good thermomechanical performance, used in high-temperature (>230°C) applications. Pis based on aromatic diamines and dianhydrides exhibit excellent heat resistance. In addition to their outstanding high-temperature resistance (Sancaktar et al. 1984 Sancaktar and Schenck 1985 Sancaktar and Dembosky 1986), toughness and good dielectric properties, low flammability, and high radiation resistance are desirable characteristics for this class of adhesives. 

Sauer, B. B. Hsiao, B. S.and Faron, K. L., Miscibility and phase properties of poly(aryl ether ketone)s with three high temperature all-aromatic thermoplastic polyimides, PoZymer, 37 (3), 445 53 (1996). 

Sheth, K. C. R. Gallucci, R. R.and Haralur, G., Thermoplastic polyimide - poly-etheretherketone blends with exceptional high temperature properties, ANTEC 2008, Proceedings of the 66th Annual Technical Conference Exhibition, Milwaukee, WI, 4-8.05.2008, Society of Plastics Engineers, pp. 794-797. 

Iwata, M. Suzuki, M. Kazama, K. Ando, A. Miyauchi, M. Ishida, Y. and Yokota, R., Properties of newly developed thermoplastic polyimide and its durability under proton, electron, and UV irradiations. Proceedings of the 11th International Symposium on Materials in Space Environment, 15-18.09.2009, Aix-en-Provence, France. 

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