Metal-Free Anionic aPolymerization of n-Hexyl Isocyanate Catalyzed by Phosphazene Bases

Abstract

Metal-free anionic polymerization of n-hexyl isocyanate (HIC) catalyzed phosphazene bases in THF at −98 °C under 10−6 Torr was attempted to obtain peptide-mimic poly(n-hexyl isocyanate) (PHIC) with high purity. tert-Butylimino-tris(dimethylamino)phosphorene (t-BuP1), 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-BuP2), and 1-tert-Butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)-phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene) (t-BuP4) with the characteristic orders of basicity and bulkiness (t-BuP1 < t-BuP2 < t-BuP4) were used as catalysts to activate the N-phenethyl-3-phenylpropanamide ((PhEt)2OCNH). Among them, only t-BuP2 and t-BuP4 generated the initiating amidate anions paired with each phosphazenium cation. The catalysis of t-BuP2 and t-BuP4 produced PHICs with the MWs higher than the theoretical ones and the characteristic ranges of dispersities depending on the phosphazene type, in which moderately low dispersities were achieved by t-BuP2 due to tight ionic bond between propagating chain-end and protonated phosphazene. The anionic polymerization of HIC catalyzed by t-BuP2 with molar feed ratios monomer to initiator ([HIC]0/[NaPEPPA]0) within 207−801 produced PHICs with high yields (96.9−98.7%) and MWs (Mn = 44.1−174 kDa, Đ = 1.37−1.64) linearly controlled by the feed ratios.