Preparation of Hyperbranched Aromatic Polyimides via A2 + B3 Approach

Abstract

Two novel B3 monomers, tri(phthalic anhydride) and tri(phthalic acid methyl ester), were synthesized. Hyperbranched polyimides were prepared by A2 + B3 polymerizations of (a) 1,4-phenylenediamine (A2) and tri(phthalic anhydride) (B3) (method A) and (b) 1,4-phenylenediamine (A2) and tri(phthalic acid methyl ester) (B3) (method B) in a 1:1 molecular ratio. Gelation was effectively avoided in the A2 + B3 polymerization by method B and a dramatic inherent viscosity increase at the critical polymerization concentration was observed. The high viscosity phenomena, generally observed in the preparation of hyperbranched polymers through the A2 + B3 approach, are elucidated by the hyperbranched structure (dendritic, linear, and terminal content) characterization for polyimides with different viscosities. The self-standing films were successfully prepared from the hyperbranched precursors by the casting method. The results indicate that the weight-average molecular weight of hyperbranched precursors are ranged from 33 600 to 125 000 and their inherent viscosities are varied from 0.17 to 0.97 dL/g. The degree of branching (DB) of hyperbranched polyimides is estimated to be 0.52−0.56 by 1H NMR measurement. Their glass transition temperatures measured by differential scanning calorimetry (DSC) range from 212 to 236 °C. The 5% weight loss temperatures of films, measured by thermogravimetric analysis (TGA), are around 500 °C. Their tensile storage modulus by dynamic mechanical thermal analysis (DMA) attains 4.0 Gpa, similar to that of their linear analogues.