New thermostable systems: 1. Mechanism and kinetics of polycondensation and characterization of fluoro-nadimide end-capped oligomers
Résumé
The reactivity of monomers in PMR (polymerization of monomeric reactants) mixtures has been investigated in methanol at room temperature. The monomers used were three aromatic diamines, meta-phenylene diamine (mPDA), para-phenylene diamine (pPDA), the 9,9-bis(4-amino phenyl) fluorene (Cardo diamine), hexafluoroisopropylidene-2,2 bis phthalic ether (HFDE) and nadic anhydride mono methyl ester (NE). Using titration, and 13C and 19F NMR, it was found that NE rapidly reacts with the three aromatic diamines to yield bisnadimides; the corresponding acid-amide intermediates were not detected. The diester HFDE, on the other hand, reacts only very slowly with the same diamines at room temperature in methanol. Telechelic polyimides with nadic terminations were prepared from these monomers and characterized with liquid phase 1H and 13C NMR and HPLC. This physico-chemical study showed that during synthesis, the endo (N) nadimides isomerize giving off a mixture of endo endo (NN), endo exo (NX) and exo exo (XX) end groups. In addition, a fine high-performance liquid chromatography analysis led to the separation of oligomers as a function of their polymerization degree, and for each molecular weight a mixture of isomeric chain end groups NN, NX, XX were separated.