AbstractLanthanum isopropoxide was found to serve as a novel anionic initiator for the polymerization of hexyl isocyanate affording poly(hexyl isocyanate) with very high molecular weight (Mn>106) under appropriate conditions. Other lanthanoid alkoxides, such as samarium, ytterbium and yttrium isopropoxides, also brought about the polymerization of hexyl isocyanate. Butyl, isobutyl, octyl andm‐tolyl isocyanates also underwent the polymerization reaction to form the corresponding polymers by using lanthanum isopropoxide as initiator, while polymerizations oftert‐butyl and cyclohexyl isocyanates with lanthanum isopropoxide did not occur under identical conditi