To study living anionic polymerization, 3-(triethylsilyl)propyl isocyanate (TEtSPI) monomer was synthesized by hydrosilylation of allylamine with triethylsilane and treatment of the resulting amine with triphosgene. The polymerization of TEtSPI was performed with sodium naphthalenide (Na-Naph) as an initiator and in the absence and presence of sodium tetraphenylborate (NaBPh4) as an additive in tetrahydrofuran (THF) at - 78 and at - 98 degreesC. A highly stabilized amidate anion for living polymerization of isocyanates was generated for the first time with the combined effect of the bulky substituent and the shielding action of the additive NaBPh4, extending the living character at least up to 120 min at - 98 degreesC. Even the anion could exist at - 78 degreesC for 10 min. A block copolymer, poly(n-hexyl isocyanate)-b-poly[(3-triethylsilyl)propyl isocyanate]-b-poly(n-hexyl isocyanate), was synthesized with quantitative yields and controlled molecular weights via living anionic polymerization in THF at -78 degreesC for TEtSPI and -98 degreesC for n-hexyl isocyanate, respectively, with Na-Naph with three times of NaBPh4 as a common ion salt. (C) 2004 Wiley Periodicals, Inc.