To prepare ultrahigh molecular weight (UHMW) poly(N-vinylcarbazole) (PVCZ) with a high conversion, I heterogeneous-solution-polymerized N-vinylcarbazole (VCZ) in methanol/tertiary butyl alcohol (TBA) at 25, 35, and 45 degreesC with a low-temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN), and I investigated the effects of the polymerization conditions on the polymerization behavior and molecular parameters of PVCZ. A low-polymerization temperature with ADMVN, a heterogeneous system with methanol, and a low chain transfer with TEA proved to be successful in obtaining PVCZ of UHMW [weight-average molecular weight (M-w) > 3,000,000] and high conversion (>80%) with a smaller temperature rise during polymerization but still of free-radical polymerization by an azoinitiator. The polymerization rate of VCZ in methanol/TBA at 25 degreesC was proportional to the 0.97 power of the ADMVN concentration, indicating a heterogeneous nature for the polymerization. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ produced in methanol/TBA at 25 degreesC with an ADMVN concentration of 0.0001 mol/mol of VCZ, an M-w of 3,230,000 was obtained, with a polydispersity index of 2.4. (C) 2001 John Wiley & Sons, Inc.