Polymerization by [3 + 2] cycloaddition, 3. Polyimides

The reaction between hexafluoroacetone azine and bis(bicyclo[2.2.1]hept-5-en-2,3-dicarboximide)s ( 5 and 6 ) (dinadimides) (mole ratio 1:1) yields polymers with number-average molar masses between M?_n = 1700 and M?_n = 5700 depending on the reactants. The possible isomeric structures of the polymers are discussed in detail. From steric considerations which are supported by ¹³C and ¹⁹F NMR spectral data the number of realized isomers is reduced from sixteen to only three ( 12, 13 and 14 ). In contrast to these results, hexafluoroacetone azine and dimaleimides do not react to form polymers. This is explained on the basis of a spontaneous rearrangement of the primarily formed 1:1 adduct to 1 H-pyrazolines.