Characteristics of hydrogels formed by assocn. of hydrophobically-modified polyethylene glycol (PEG) with fluoroalkyl (Rf) end-groups can be controlled by modulating their mol. structures. Polymers with relatively long PEG chains (e.g., 20 kg/mol PEG with C-10 Rf) follow the typical single-phase, continuous transition from sol to gel. As the PEG length is reduced relative to fluoroalkyl length (10 kg/mol PEG with C-8 or C-10 Rf) the phase behavior changes to sol-gel coexistence (\"two-phase\" type) behavior. This correlates with changes in the rheol. properties of the gel and in its erosion behavior. Finally, for sufficiently short PEG length the polymer ppts. into a concd. gel with negligible soly. in water. [on SciFinder (R)]