Radical copolymerization of N-(azo dye) maleimide or N-(substituted phenyl) maleimide and styrene were carried out using 2,2’-azobis-isobutyronitrile as an initiator in THF at 60 degrees C. These copolymers exhibit high solubility in most of the organic solvents and excellent thermal stability up to 280 degrees C under nitrogen atmosphere. The copolymer films which were heated at 200-240 degrees C under high corona field exhibit d(33) = 3-5 pm/V, in the Maker-fringe measurement. Experimental results also showed that the copolymer with azo dye as chromophore did not decay in second harmonic response even at 130 degrees C.