A series of functional copolymers was synthesized by an emulsion polymerization of N-ethylaniline (EA) and aniline (AN) in the presence of sodium dodecylbenzene sulfonate in HCl. Several important polymer parameters including the polymerization yield, molecular weight, solubility, film formability, solvatochromism, thermochromism, and alterable electrical conductivity were systematically studied by changing the comonomer ratio, emulsifier/monomer ratio, oxidant/monomer ratio, solvent, and temperature. The resulted copolymers were characterized in detail by infrared and UV-vis spectroscopies. It is found that these copolymers exhibit narrow molecular weight distribution, good solubility, excellent film flexibility, colorful solvatochromism, in various solvents, reversible thermochromism in a wide temperature range, and widely controllable conductivity from 2.03 X 10(-10) to 0. 161 S/cm with changing the polymerization conditions and doping states. (C) 2004 Elsevier Ltd. All rights reserved.