New copolymers of thiophenes containing azobenzene moieties in the side chain, 3-((((((4-phenyl)azo)phenoxy)ethyl)triethoxy)oxy)-4-methylthiophene/3-me thyltetra (oxyethylene)oxy-4-methylthiophene (CP1) and 3-((((((4-phenyl)azo)phenoxy)ethyl) triethoxy) oxy)-4-methylthiophene/3-dodecylthiophene (CP2), were synthesized from 3-bromo-4-methylthiophene. These copolymers were characterized by H-1-NMR spectroscopy, and their thermal, optical, and electrochemical properties were determined by thermogravimetric analysis, differential scanning calorimetry, absorption spectroscopy, and cyclic voltammetry. CP1 possesses higher degree of conjugation and azobenzene content than CP2, and its structure is more regio-regular. Besides, CP1 exhibited a higher glass transition temperature (T (g) = 35 A degrees C, T (5) = 225 A degrees C) and a lower thermal stability than CP2 (T (g) = 13 A degrees C, T (5) = 307 A degrees C). Both copolymers showed a similar solvatochromic behavior when they were dissolved in chloroform and mixtures chloroform:methanol.