Interphase oligomerization of thiophene within a supported thin film is described. Polyethylene (PE) surfaces containing an irregularly hyperbranched poly(acrylic acid) (PAA) graft were first prepared by multistep grafting of poly(tert-butylacrylate) onto oxidized PE. The product ultrathin PAA grafts were then further modified by amidation or esterification with thiophenes containing amino or hydroxyl groups to form new interfaces containing thiophene monomers. These thiophene-modified grafts were characterized by attenuated total reflectance infrared spectroscopy and were shown to be suitable as substrates in an oxidative polymerization method with FeCl3 as an oxidant. The product 2,5-coupled thiophene oligomers (3-PAA/PE-oligomerized thiophene ester, OTE) emitted a yellow-green light under UV irradiation, indicating that a conjugated fluorescence oligothiophene had been prepared within these hyperbranched films.