We report the propagation-inspired initiation of sodium N-phenethyl-3-phenylpropanamide (NaPEPPA), an aliphatic sodium amidate, for the living anionic homo- and copolymerization of isocyanates. This initiator was compared with sodium benzanilide (NaBA), an aromatic sodium amidate, in the living anionic homopolymerization of n-hexyl isocyanate (HIC). Only NaPEPPA attained the initiation efficiencies close to unity at the early stage of propagation. The homopolymerization with [HIC](0)/[NaPEPPA](0) = 38.9/85.1/203 led to poly(n-hexyl isocyanate)s (PHICs) with predictable MWs and low dispersities (M-n,M-theo = 5.12/10.7/24.7 kDa; M-n = 5.22/11.1/27.4 kDa; D = 1.11/1.10/1.06). NaPEPPA was also used to initiate the living anionic copolymerization of HIC and furfuryl isocyanate (FIC). As a result, poly(furfuryl isocyanate-block-n-hexyl isocyanate) (P(FIC-b-HIC)) was afforded by the blocky monomer sequence distribution. Based on the copolymerization kinetics, a series of polyisocyanate-based multiblock copolymers, P(FIC-b-HIC)(1)/P(FIC-b-HIC)(2)/P(FIC-b-HIC)(3)/P(FIC-b-HIC)(4) (M-n,M-theo = 5.47/10.6/15.8/20.8 kDa; M-n = 5.59/11.5/16.3/20.3 kDa; D = 1.10/1.03/1.03/1.03), were afforded by the repetitive sequential addition of comonomers.