Facile synthesis of hyperbranched polyimides from A₂ + BB′₂ monomers

Facile syntheses of hyperbranched polyimides were realized by the polymerization of A₂ + BB′₂ monomers, 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA) + 2,4,6-triaminopyrimidine (TAP), performed by mixing the monomers together in N-methylpyrrolidone at 17% w/v concentrations with molar ratios of 6FDA:TAP ranging from 1:1 to 2:1. The lower reactivity of 2-amino as compared with 4-/6-amino in TAP, demonstrated by ¹H NMR, was probably the main reason for no gelation formed during the polymerization although monomer conversions surpassed the theoretical gel points. Fourier transform infrared spectroscopy and NMR were used to verify the structures of the obtained polymers. ¹H NMR analysis indicated the degrees of branching (DB) of the polymers increased from 36 to 83% with the molar ratios of 6FDA:TAP increasing from 1:1 to 2:1. Molecular weights were determined by gel permeation chromatography, and inherent viscosities were measured. Glass-transition temperature values, determined by differential scanning calorimetry, decreased when DB increased, and thermogravimetric analysis reflected the excellent thermal stability of the obtained hyperbranched polyimides.