A general approach to the synthesis of second-order nonlinear optical (NLO) polyimides exhibiting high thermal stability has been developed. Several selected NLO chromophores have been incorporated into the polyimide backbone. Detailed physical studies showed that these polymers are very promising for practical applications. Three of these polyimides are soluble in common organic solvents, offering the ease of processing. High glass temperatures, around 230 degrees C, assure a long-term NLO stability at elevated temperatures, such as 150 degrees C. Low optical loss was observed for those soluble polymers. The synthetic approach is also versatile and will allow the syntheses of many other functional polymers.