A triamine monomer, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), was synthesized from phloroglucinol and 4-chloronitrobenzene, and it was successfully polymerized into soluble hyperbranched polyimides (HB Pis) with commercially available dianhydrides: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4'-oxydiphthalic anhydride (ODPA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA). Different monomer addition methods and different monomer molar ratios resulted in HB PIS with amino or anhydride end groups. From H-1 NMR spectra, the degrees of branching of the amino-terminated polymers were estimated to be 0.65, 0.62, and 0.67 for 6FDA-TAPOB, ODPA-TAPOB, and BTDA-TAPOB, respectively. All polymers showed good thermal properties with 10% weight-loss temperatures (T-10's) above 505 degreesC and glass-transition temperatures (T-g's) of 208-282 degreesC for various dianhydrides. The anhydride-terminated HB PIS showed lower T-10 and T-g values than their amino-terminated counterparts. The chemical conversion of the terminal amino or anhydride groups of the 6FDA-based polyimides into an aromatic imido structure improved their thermal stability, decreased their T-g, and improved their solubility. The HB PIS had moderate molecular weights with broad distributions. The 6FDA-based HB PIS exhibited good solubility even in common low-boiling-point solvents such as chloroform, tetrahydrofuran, and acetone.