Synthesis and characterization of hyper-branched polyimides from 2,4,6-triaminopyrimidine and dianhydrides system

A series of aromatic hyper-branched polyimides were successfully prepared by condensation polymerization of commercially available A₂-type dianhydride monomers 4,4-biphthalic anhydride (BPAD) and 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (DSDA) with the BB₂′-type triamine monomer 2,4,6-triaminopyrimidine (TAP). The hyper-branched polyimides, with two different terminated groups, were obtained from the reactions between different molar ratios of the TAP and the dianhydrides. Both Fourier transform infrared (FT-IR) and ¹H NMR spectroscopy were used to verify the molecular structures of the obtained hyper-branched polyimides. The molecular weights were determined by gel permeation chromatography (GPC). The results suggested that the amine-terminated hyper-branched polyimides displayed lower degrees of branching and molecular weights than the corresponding anhydride-terminated ones. However, the anhydride-terminated hyper-branched polyimides showed a relatively lower glass transition temperature, obtained by differential scanning calorimetry, which could be attributed to the increased free volume and mobility of the macromolecules caused by the absence of chain-end interactions. Thermogravimetric analysis (TGA) results indicated that the hyper-branched polyimides had excellent thermal stabilities, the amine-terminated hyper-branched polyimides showing higher thermal stabilities than those of the anhydride-terminated ones.