article · ACS Macro Letters
Anionic ring-opening polymerisation offers a route to synthetic polymers, but avoiding metallic catalysts remains an important objective in polymer chemistry. This research examines the use of organic superbases, such as phosphazene and Verkade base, paired with an initiator to synthesise metal-free poly(sulfonylaziridine)s from various N-sulfonyl aziridines. Catalytic activity correlated directly with base strength. Among the tested catalysts, the phosphazene superbase t-Bu-P4 and the Verkade base TiPP facilitated controlled polymerisation of 2-methyl-N-tosylaziridine. The phosphazene catalyst delivered superior results, generating well-defined polymers with high molar masses exceeding 30 kilograms per mole and narrow dispersities under 1.10 within three and a half hours. It also effectively polymerised less reactive monomers, achieving high conversions above 95 percent. Furthermore, the method functioned efficiently with catalyst loadings as low as 0.05 mole percent, requiring substantially less catalyst than initiator while preserving polymer chain propagation.
Producing high-quality polymers typically relies on metal-based catalysts, which can leave undesirable residues that are difficult to remove. Demonstrating that organic superbases can achieve precise, living polymerisation provides a reliable, metal-free alternative. This offers cleaner synthesis pathways for researchers aiming to produce specialised materials with controlled molecular weights, low dispersity, and minimal catalyst loading.
This work represents early-stage synthetic research into metal-free specialty polymers. Polymer manufacturers and chemical synthesis companies seeking to eliminate metallic impurities from functional materials could potentially adopt these superbase catalysts. However, the abstract does not indicate specific product applications, market testing, or scalability beyond laboratory reactions, meaning significant developmental and process engineering work would be required to establish commercial viability.
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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 (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 %.
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DOI: 10.1021/acsmacrolett.7b00775
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