Polyimides, epoxy toughener

Relevant systems are mbber-toughened epoxy resins, high-impact acrylic (PMMA particles in mbber matrix, obtained by radical polymerization of 80/20 MMA/EVAc mixture), polyimide/silica hybrid materials (obtained using the sol-gel method), and a very high strength ( 60 MPa) mbbers (obtained by peroxide cure of a hydrogenated nitrile rubber/ zinc dimethacrylate system) [Inoue, 1995]. 

Hay Hay, J. N., Woodfine, B., Davies, M. Toughening of epoxy resins by polyimides synthesized from bisanUines. High Perform. Polym. 8 (1996) 35-56. 

One drawback with addition-type polymers is that the cured adhesive tends to be brittle. Attempts to toughen addition polyimides have met with some success, though improvements in this area are needed. The development of systems exhibiting the same level of toughness as today s state-of-the-art epoxy adhesives is a goal for the future. 

The comparatively low impact strength of many well-known polymers, such as PMMA, polystyrene and PVC, led to the production of rubber-modified thermoplastics with high impact strength. The best-known examples are high-impact polystyrene (HIPS) and ABS copolymer, where the rubbery phase is dispersed throughout the polymer in the form of small aggregates or balls. Other polymers that have been toughened in this way include PMMA, PVC, polypropylene, polycarbonate, nylons and thermosets such as epoxies, polyesters and polyimides. 

The primary intent of this article is to review the status of experimental and newly developed high temperature organic adhesives with particular attention to aerospace materials. Detailed information on the synthesis of various polymers or bonding conditions can be obtained in the references cited. Several high temperature adhesives are commercially available, and information on these systems can be obtained from the major adhesive suppliers. For aerospace use, these consist primarily of modified epoxy phenolics, toughened bismaleimides, addition and condensation polyimides. 

It is of interest to note that before the advent of the bismaleimides, and the polyimides in general, high service temperatures were achieved using combinations of solid Bisphenol A-based epoxies with conventional phenolic resoles the interaction between phenolic and epoxy often being promoted by the incorporation of dicyandiamide. The first toughener for high temperature matrices, namely finely divided aluminium powder, was also incorporated into these formulations. ... 

Cross- linked Epoxies Diacrylics Polyimide Polyurethane P/F R/F M/F Toughened acrylics Polyvinyl formal-P/F Nitrile phenolic ... 

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