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Fundamental Kinetics of Living Anionic Polymerization of Isocyanates Emerging by the Sodium Diphenylmethane-Mediated Initiation

Author:
Chae, Chang-Geun, Bak, In-Gyu, Lee, Jae-Suk
Source:
Macromolecules 2018 v.51 no.17 pp. 6771-6781
ISSN:
1520-5835
Subject:
anions, copolymerization, molecular weight, sodium
Abstract:
Anionic polymerization of n-hexyl isocyanate (HIC) in THF at −98 °C under 10–⁶ Torr for the kinetic study was performed by the initiation of sodium diphenylmethane (NaDPM) in either the absence or presence of sodium tetraphenylborate (NaBPh₄; [NaBPh₄]₀/[NaDPM]₀ = 0 or 5). The common-ion effect of NaBPh₄ to suppress the formation of unstable free amidate anions led to termination-free propagation by amidate ion pairs. In [HIC]₀/[NaDPM]₀ = 50.8/101/201, the initiation of NaDPM early reached ∼100% efficiencies during propagation, which led to the yield of poly(n-hexyl isocyanate)s (PHICs) with predictable molecular weights (Mₙ,ₜₕₑₒ = 6.50/12.7/24.7 kDa; Mₙ = 6.50/12.7/26.1 kDa) and low dispersities (Đ = 1.06/1.07/1.15). Within the conditions, the rate of propagation accorded with a first-order dependence on [NaDPM]₀, indicating that the propagating amidate ion pairs are intrinsically unimeric (nonassociated). Kinetics of anionic copolymerization of HIC and allyl isocyanate (AIC) exhibited a monomer distribution toward a tapered block sequence.
Agid:
6130170