The temporal change of complex viscosity (eta*) of two plates consisting of an end-functional monocarboxylated polystyrene (PSmCOOH) and poly(methyl methacrylates) (PMMA) with various amounts of poly(methyl methacrylate-ran-glycidyl methacrylate) (PMMAGMA) was measured by a rotational rheometer. There were three distinct stages for the change of eta* with time: (i) stage I, where eta* increased rapidly at short times and approached a steady value at later times; (ii) stage II, where eta* did not change; and (iii) stage III, where eta* increased slowly again and reached a final value. The apparent reaction kinetics obtained from the results in stage I was a first-order reaction. The change of the interfacial roughness between two plates with reaction time was investigated by transmission electron microscopy and atomic force microscopy after selective removal of unreacted PSmCOOH layer. At long reaction times, the interface became pinched off, and then microemulsions (and micelles) were formed in the PMMA phase.