User:Siva29prakash

= Bismaleimides = Bismaleimides are addition-type polyimides used in high-performance materials used in the Polymer Matrix Composites (PMCs). In general, bismaleimides can have a service life off 20000 hours at 200 °C. These materials are high cost to low volume in consumption.

Monomers are usually synthesized from maleic anhydride and an aromatic diamine. The double bond of the maleimide is very reactive and can undergo chain-extension reactions. Bismaleimides can provide a higher service temperature than epoxies, while maintaining epoxy-like processing.

Monomer synthesis
The synthesis of bismaleimide consist of two steps. Synthesis of bisamic acid followed by the dehydration of bisamic acid to form bisamleimide.

Synthesis of bisamic acid
The synthesis of bisamic acid starts with the two moles of maleic anhydride and one mole of aromatic diamine in the acetone medium. The mechanism of formation of bisamic acid involved in the nucleophilic attack of the amino group on the carbonyl carbon of the maleic anhydride group which opens the anhydride ring to form the amic acid group.

Synthesis of bismaleimide
In this step the amic acid dehydrates in the presence of sodium acetate and anhydrous acetic acid by the cyclic imdization of acid with the secondary amine.

Thermal properties
The bismaleimdes shows a endothermic melting behavior from 150 °C to 200 °C with an enthalpy from 50 to 100 J/g. The curing or crosslinking proceeds from 180 °C to 250 °C with an enthalpy from 200 to 300 J/g. In general, these materials are thermally stable up to 400 °C.

Curing of bismaleimide
In general the bismaleimides are thermally cured. The imide double bonds cannot be photocured. The curing of this bismaleimide involves 3 dimensional network structure with high amount of cross linking density per unit volume. This thermal curing leads to cross linking contains some amount of cyclization of the imides and other network structures.