A series of well-defined poly(arylene ether sulfone)s were synthesized (1P-4P) by chain-growth condensation polymerization with amide initiators having various numbers of initiating sites. Differential Scanning Calorimetry (DSC) study of the polymers revealed that branched polymers (3P and 4P) had higher glass transition temperatures (T-g) than linear polymers (1P and 2P) when they had the identical concentration of end groups. However, the viscosity of the polymers decreases as the number of branches increase due to the change of the hydrodynamic volume. Interestingly physical gelation of THF solution of these polymers was observed. Analyses of the self-assembled structure by FE-SEM, FE-TEM, temperature-dependent H-1 NMR, FT-IR, and XRD indicated that the formation of fibrillar network was driven by the hydrogen bonding of aromatic amides.