Nonconjugated bipolar transport polymers have been developed as host materials for electroluminescent devices by incorporating both electron-tran sporting and hole-tran sporting functionalities into copolymers. The random copolymer PCt-nvk3-7 containing mesogen-jacketed segment of P-Ct have been synthesized and characterized. The effect of mesogen-jacketed segment content of these bipolar copolymers on device performance has been investigated. The results of polymer light-emitting diodes (PLEDs) show that the jacketed content of copolymers has a significant effect on device performance: lowering charge transport and facilitating the hole-electron recombination leads to much higher current efficiency. Applying these high triplet random copolymers as host, the maximum current efficiency of 0.70 cd/A and the maximum brightness of 1872.8 cd/m(2) was achieved for PCt-nvk3-7 with an orange-emitting complex dopant. The results suggest that the bipolar copolymers PCt-nvks can be good host polymers for electrophosphorescent devices. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7861-7867, 2008