Synthesis, characterization and properties of TAP-6FDA hyperbranched polyimides with different branching degrees.

A series of hyperbranched polyimides were successfully synthesized by condensation polymerization of A₂-type dianhydride monomer 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA) and B′B₂-type triamine monomer 2,4,6-triaminopyrimidine (TAP). Polymers with different branching degrees (DB) and terminated groups were obtained by changing the monomer addition order and the monomer molar ratio. Fourier transform infrared spectroscopy and ¹H NMR were used to verify the structure of the prepared polyimides, which indicated that the amino group still existed in all the products. The DB of the polymers indicated by ¹H NMR increased from 30% to 79% with the molar ratio of TAP:6FDA decreasing from 1:1 to 1:2. The absolute molecular weights were measured by size-exclusion chromatography with multi-angle laser light-scattering detection, which suggested that the highest molecular weight would be obtained when the molar ratio of amino groups:anhydride groups of the monomers was 3:3.2. With the DB increasing, the d-spacing values indicated by wide angle X-ray diffraction increased from 5.15 Å to 5.68 Å and the UV − visible spectra of the polymers exhibited decreasing cut-off wavelengths. The 5% weight loss temperature in nitrogen increased with decreasing content of TAP monomer, and the glass transition temperatures of the obtained polyimides decreased from 282 °C to 258 °C with increasing DB. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]