New thermostable systems: 1. Mechanism and kinetics of polycondensation and characterization of fluoro-nadimide end-capped oligomers

The reactivity of monomers in PMR (polymerization of monomeric reactants) m ixtures has been investigated in methanol at room temperature. The monomers used were three aromatic diamines, meta-phenylene diamine (mPDA), pam-phen ylene diamine (pPDA), the 9,9-bis (4-amino phenyl) fluorene (Cardo diamine) , hexafluoroisopropylidene-2,2 bis phthalic ether (HFDE) and nadic anhydrid e mono methyl eater (NE). Using titration, and C-13 and F-19 NMR, it was fo und that NE rapidly reacts with the three aromatic diamines to yield bisnad imides; the corresponding acid-amide intermediates were not detected. The d iester HFDE, on the other hand, reacts only very slowly with the same diami nes at room temperature in methanol. Telechelic polyimides with nadic termi nations were prepared from these monomers and characterized with liquid pha se H-1 and C-13 NMR and HPLC. This physico-chemical study showed that durin g 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 h igh-performance liquid chromatography analysis led to the separation of oli gomers as a function of their polymerization degree, and for each molecular weight a mixture of isomeric chain end groups NN, NX, XX were separated.