Synthesis and Comparison of Hyperbranched Aromatic Polyimides Having the Same Repeating Unit by AB2 Self-Polymerization and A2 + B3 Polymerization

A new AB 2 monomer, designed from a template of the repeating unit of the hyperbranched polyimides by nonideal A 2 + B 3 polymerization, was successfully prepared via a multistep synthesis. Hyperbranched polyimides, having the same repeating unit as that by nonideal A 2 + B 3 polymerization, were prepared from this new AB 2 monomer by direct self-polycondensation in the presence of diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl)phosphonate (DBOP). Hyperbranched polyimides, with a molecular weight of 1.11 × 10 4 to 1.73 × 10 5 and an inherent viscosity of 0.12−0.17 dL/g, were obtained. As-prepared hyperbranched polyimides were soluble in DMF, DMAc, DMSO and NMP. By 1 H NMR analysis, the degree of branching (DB) of the prepared hyperbranched polyimides was estimated to be around 0.50. By thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurement, their 5% weight loss temperatures and glass transition temperatures were found to be in the ranges 445−460 and 155−161 °C, respectively. A comparison between the hyperbranched polyimides by AB 2 self-polymerization and nonideal A 2 + B 3 polymerization reveals that their physical properties, such as viscosity, thermal stability, and glass transition temperature, etc., are different from each other. Especially, a comparison between the plots of intrinsic viscosity [ η ] vs molecular weight M w elucidates that their molecular shapes are also different each other. The examination of the chain entanglement and intermolecular interaction by employing a freeze-extracting technique reveals that hyperbranched polyimides by nonideal A 2 + B 3 polymerization have a certain extent of chain entanglement and intermolecular interaction. A comprehensive analysis finally suggests that hyperbranched polyimides by AB 2 self-polymerization have a compact highly branching structure, while that by nonideal A 2 + B 3 polymerization have a low branching density topology.