40207_04HIGH TEMPERATURE RESINS - H IGH TEMPERATURE RESINS...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
HIGH TEMPERATURE RESINS 4 Hugh H. Gibbs 4.1 INTRODUCTION The high temperature resins discussed in this chapter are defined as a family of aromatic polyimides having glass transition tempera- tures (TJ greater than 316°C (600°F). Other resin systems such as the bis-maleimides and various aromatic thermoplastics (including lower Tg thermoplastic polyimides) are dis- cussed in Chapters 5 and 6 respectively. Over the years it has been found that the key to achieving outstanding high temperature mechanical properties and thermal-oxidative stability is to have a polymer made with aro- matic heterocyclic repeat units where there is a minimum aliphatic content (e.g. aliphatic C-H and C=C groups). Such groups can contribute to thermal-oxidative instability. Although many types of aromatic heterocyclic polymers are possible, one type, polyimides, has turned out to be the most commercially successful. The highly aromatic character achievable in such polymers is the reason behind their ther- mal-oxidative stability. Also, provided that flexibilizing linkages in the monomers are kept to a minimum, the mherent rigidity of the repeat units results in the high T which is essential if an adequate level of hi& tempera- ture mechanical property retention is to be achieved. Over the past 25 years various strategies have been developed to introduce processibil- ity into aromatic polyimides without detracting Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 too much from their high temperature mechan- ical properties and thermal-oxidative stability. As a result of a extensive work on the part of polymer scientists, mostly within the USA, a wide variety of products has been developed possessing various trade-offs between their processibility and properties. In writing this chapter the author has attempted to explain the evolution of high temperature polyimides as matrix resins for advanced composites together with a description of their processing character- istics (where available), physical properties and long term high temperature performance. 4.2 CONDENSATION POLYIMIDE CHEMISTRY 4.2.1 GENERAL COMMENTS ON CONDENSATION POLYMERIZATION Studies carried out in DuPont in the 1950s and 1960s established that polyimides can be pre- pared by the reaction of an aromatic dianhydride and an aromatic diamine in a polar solvent such as dimethyl acetamide or N- methyl-2-pyrrolidone (NMP). This is illustrated in Fig. 4.1 for the polyimide based on pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA). The intermediate polyamide acid solution is the basis for DuPont's Pyre ML@ wire enamel. During the second step, the imidization of the polyamide acid, 2 moles of water are eliminated per repeat unit. Two other DuPont products, Kapton@ polyimide film and Vespel@ SP polyimide pre- cision parts are also based on this chemistry.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
76 High temperature resins 4.4-Oxydianiline ti ti Pyromellitic Dianhydnde i Heat (PMDA) (ODA) (-2H,O) 0 0 PMDAiODA Polyamide Acid n (-solvent) +N:~~;N~o+ / C' 0 0 n II PMDAiODA Polyimide Fig. 4.1
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 24

40207_04HIGH TEMPERATURE RESINS - H IGH TEMPERATURE RESINS...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online