Preparation of hyperbranched aromatic polyimides via A2+B3 approach

Two novel B-3 monomers, tri(phthalic anhydride) and tri(phthalic acid methyl ester), were synthesized. Hyperbranched polyimides were prepared by A(2) + B-3 polymerizations of (a) 1,4-phenylenediamine (A2) and tri(phthalic anhydride) (B-3) (method A) and (b) 1,4-pllenylenediamine (A(2)) and tri(phthalic acid methyl ester) (B-3) (method B) in a 1:1 molecular ratio. Gelation was effectively avoided in the A(2) + B-3 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 A(2) + B-3 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 H-1 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 degreesC. Their tensile storage modulus by dynamic mechanical thermal analysis (DMA) attains 4.0 Gpa, similar to that of their linear analogues.