Poly imide relative stability

In light of the higher imidization temperatures associated with poly(amic alkyl esters), this approach could be extended to yield improved coating formulations [82]. Since it was now possible to balance the relative reactivity of the chain-extender with the imidization temperature of an oligofamic alkyl ester), here R = methyl, ethyl, etc., less reactive chain-extenders could be utilized. The lower reactivity of the chain-extender would be reflected in improved solution stability and shelf-life of the formulation without sacrificing the mechanical properties of the final polyimide, see Table 10 where EGX, TFE,... 

The cured or fully imidized polyimide, unlike the poly(amic acid), is insoluble and infusible with high thermooxidative stability and good electrical-insulation properties. Thermoplastic polyimides that can be melt processed at high temperatures or cast in solution are now also available. Through an appropriate choice of the aromatic diamine, phenyl or alkyl pendant groups or main-chain aromatic polyether linkages can be introduced into the polymer. The resulting polyimides are soluble in relatively nonpolar solvents. 

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