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Organocatalyzed Anionic Ring-Opening Polymerizations of N‑Sulfonyl Aziridines with Organic Superbases
journal contribution
posted on 2017-11-14, 18:52 authored by Xin Wang, Yaya Liu, Zhenjiang Li, Haixin Wang, Hailemariam Gebru, Siming Chen, Hui Zhu, Fulan Wei, Kai GuoThe
anionic ring-opening polymerizations (AROPs) of N-sulfonyl aziridines, in the presence of organic superbases including
phosphazene (t-Bu-P4), Verkade’s
base (P(i-PrNCH2CH2)3N, TiPP), DBU, MTBD, and N,N,N′,N′-tetramethylguanidine
(TMG), using N-benzyl-p-toluenesulfonamide
(BnN(H)Ts) as initiator were explored to produce metal-free poly(sulfonylaziridine)s.
Among the superbases used, the catalytic activity was found directly
proportional to their basicity. Remarkably, t-Bu-P4 and TiPP gave a living/controlled AROP of 2-methyl-N-tosylaziridine (TsMAz), where t-Bu-P4 performed better, affording the metal-free and well-defined
poly(sulfonylaziridine)s with high molar masses (Mn(SEC) > 30 kg mol–1) and low dispersities
(Đ < 1.10) in 3.5 h. For
the less reactive monomers of 2-methyl-N-ethylsulfonyl
aziridine (EsMAz) and 2-phenyl-N-tosylaziridine (TsPhAz), t-Bu-P4 showed the same excellent catalytic efficiency
(30 equiv, conv. > 95%, 5 h). The organocatalyzed AROP allowed
the
use of lower catalyst (t-Bu-P4) loading
than the amount of initiator (BnN(H)Ts), but the propagating polymer
chains were as many as the number of equivalents of the introduced
initiators, which could lower the loading of catalyst used to amounts
as low as 0.05 mol %.