Synthesis and characterization of second‐order nonlinear optical main‐chain polyurethanes containing acceptor‐substituted carbazole units

A diol monomer bearing carbazole units substituted with one acceptor group was prepred starting from 3‐formyl‐9‐(4‐hydroxybutyl)carbazole and hexamethylene bis(cyanoacetate) via Knoevenagel condensation. Main‐chain polyurethanes with acceptor‐substituted carbazole as nonlinear optical chromophores were obtained by addition polymerization of the carbazole diol monomer with various diisocyanates in tetrahydrofuran at room temperature using dibutyltin diacetate as a catalyst. These carbazole main‐chain polyurethanes were found to have glass transition temperatures in the range of 113–122°C and weight‐average molecular weights in the range of 6300–11000 g/mol. The chloroformsoluble polyurethanes could be spin‐coated into thin films with good optical quality. After poling, these films displayed reasonable second harmonic generation efficiencies. Preliminary results indicated that the polyurethanes have good thermal stability compared to analogous polymers without hydrogen bonds.