Chain-extending phenolic end-capped polyimides

Aromatic polyimides with phenolic end groups are chain-extended (molecular weight increased) by reacting them with formaldehyde, compounds capable of generating formaldehyde under the reaction conditions or hexamethylene tetramine in the presence of a catalytic amount of lime. These polyimides can be shaped and formed prior to the chain-extending. The aromatic polyimides appropriate for chain-extending are formed by the reaction of aromatic dianhydrides, aromatic diamines and phenolic compounds such as aminophenol.