Maleimide-based polyimides

C. Addition-Type Polyimides (Maleimide-based Polyimides)... 

Kinel Filled bis-maleimide-based molding polyimides Rhone-Poulenc... 

Two types of thermoset polyimides are currently prepared commercially. They are based on low molecular weight bis imides such as bis maleimides or bis-5-norbomene-2,3-dicarboximides. Due to unsaturations, the materials cross-link by free-radical mechanism into tight networks. Michael type additions of primary and secondary amines to the bis maleimides are often used to chain-extend them before cross-linking. This reduces the cross-linking density and the brittleness [115]. The materials are designated by the term PMR, for polymerizable monomeric reactants. 

The adhesives described above are limited in their resistance to elevated temperatnres for prolonged periods because of depolymerization or decomposition reactions at temperatures greater than 120-150°C. High temperature resistant structural adhesives based on polyimide, cyanate ester and bis-maleimide chemistries can withstand the higher temperatures but require more difficult cure conditions, are generally more expensive and service a smaller specialist segment of the overall sttuctural adhesive market. 

OUgomers end-capped with maleimide rings, which are known as bismaleimide (BMI) resins, exhibit thermal stability intermediate between epoxies and polyimides. BMI systems are mainly used to fabricate structural composites capable of sustaining temperatures up to 230 °C. Specific versions, such as CYTEC FM 32 and Ciba-Geigy Kerimid 601, have been developed to prepare adhesive compositions. Figure 9.17 displays a typical constitutive unit of various couunercial BMI resins based on BMI 38, prepared from maleic anhydride 37 and 4,4 -methylenebisbenzeneamine (MDA) 34. 

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