Poly(ethylene oxide) (PEO) was end-capped with short poly(methacryloyloxyethyl acrylate) (PMEA) chains. In aqueous solutions the end-blocks self-assembled, leading to flower-like polymeric micelles at low concentrations that associated through bridging at higher concentrations. Above a critical percolation concentration (C-p) a system-spanning transient network was formed. The transient self-assemblies were locked-in in situ by UV irradiation which caused photo-cross-linking of the PMEA blocks. The structure and composition of the clusters formed at C < C-p was studied by light scattering and chromatography after cross-linking and dilution. The results were compared with mean-field theory and numerical simulations. The dynamic mechanical properties of the networks formed for C > C-p were studied by oscillatory shear before, during, and after irradiation. UV radiation transformed the transient networks into permanent gels within a few seconds.