Pyrene-labeled diblock weak polyelectrolyte of poly (2-hydroxyethyl methacrylate)-b-poly (2-(dimethylamino) ethyl methacrylate) (Py-PHEMA-b-PDMAEMA) was successfully synthesized by atom transfer radical polymerization. The behavior of electric field induced diblock polyelectrolyte chain stretch in dilute solution was investigated by steady-state fluorescence spectroscopy. The effect of diblock polyelectrolyte concentration, pH value, salt concentration, and solvent viscosity on electric field-induced stretch was thoroughly investigated by the ratio (IE/IM) of excimer-to-monomer emission intensities obtained from the steady-state fluorescence spectroscopy. The results indicate that the weak diblock polyelectrolyte coil undergoes a stretching process in an external electric field, resulting in the electric field-induced stretch. An increasing polyelectrolyte concentration is advantageous to electric field-induced stretch. The degree of electric field-induced stretch is increased with the decrease of pH value by adding acid. In the presence of NaCl, the degree of electric field-induced stretch is increased with an increasing of salt concentration. However, an increase of solvent viscosity is disadvantageous to electric field-induced stretch. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013