The
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 (M
n(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 %.
A novel protocol for the activation of the Beckmann rearrangement utilizing the readily available and economical geminal dichloroimidazolidinediones (DCIDs) on a substoichiometric scale (10 mol %) has been developed. A unique self-propagating mechanism for the substoichiometric dichloroimidazolidinedione-activated transformation was proposed and validated. The substrate scope of the developed protocol has been demonstrated by 23 examples with good to excellent yields (mostly 90-98%) in a short time (mostly 10-30 min), including a substrate for synthesizing the monomer of nylon-12 and a complicated steroidal substrate on a preparative scale. This research not only unveils for the first time the synthetic potential of substoichiometric amounts of dichloroimidazolidinediones in promoting chemical transformation but also offers yet another important illustration of the self-propagating cycle in the context of the Beckmann rearrangement activated by a structurally novel organic promoter.
We firstly synthesized amphiphilic three-armed star-shaped poly(sarcosine)-block-poly(ε-caprolactone) diblock copolymers (s-PSar-b-PCLs), and investigated the solution properties and biocompatibility of the copolymers.
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