Triblock copolymers and pentablock terpolymers of n-hexyl isocyanate (H), styrene (S), and isoprene (1) of the type HSH (six samples, M-n:49-163 K, weight % of H:5-59), HIH (two samples, M-n:75 and 83.4 K, weight % of H:16 and 40), HSISH (one sample, M-n:79.4 K, weight % of H:13), and HISIH (one sample, M-n:128 K, weight % of 11:25) were synthesized by high-vacuum techniques in tetrahydrofuran at -98 degreesC with the sodium naphthalene/sodium tetraphenylborate initiating system. All materials were characterized by size exclusion chromatography, membrane osmometry, and H-1 NMR. The combined molecular characterization results revealed a high degree of molecular and compositional homogeneity. The thermal properties of the synthesized materials were examined by thermogravimetric analysis and differential scanning calorimetry. (C) 2003 Wiley Periodicals, Inc.