Abstract
Linear polyethylenimine (L-PEI), a standard for nonviral gene delivery, is usually prepared by hydrolysis from poly(2-oxazoline)s. Lately, anionic polymerization of sulfonamide-activated aziridines had been reported as an alternative pathway toward well-defined L-PEI and linear polyamines. However, desulfonylation of the poly(sulfonyl aziridine)s typically relied on harsh conditions (acid, microwave) or used a toxic solvent (e.g., hexamethylphosphoramide). In addition, the drastic change of polarity requires solvents, which keep poly(sulfonyl aziridine)s as well as L-PEI in solution, and only a limited number of strategies were reported. Herein, we prepared 1-(4-cyanobenzenesulfonyl) 2-methyl-aziridine (1) as a monomer for the anionic ring-opening polymerization. It was polymerized to well-defined and linear poly(sulfonyl aziridine)s. The 4-cyanobenzenesulfonyl-activating groups were removed under mild conditions to linear polypropylenimine (L-PPI). Using dodecanethiol and diazabicyclo-undecene (DBU) allowed ≥98% desulfonylation and a reliable purification toward polyamines with high purity and avoiding main-chain scission. This method represents a fast approach in comparison to previous methods used for postpolymerization desulfonylation and produces linear well-defined polyamines. The high control over molecular weight and dispersities achieved by living anionic polymerization are the key advantages of our strategy, especially if used for biomedical applications, in which molecular weight might correlate with toxicity. The synthesized polypropylenimine was further tested as a cell-transfection agent and proved, with 16.1% transfection efficiency of the cationic nanoparticles, to be an alternative to L-PEI obtained from the 2-oxazoline route. This general strategy will allow the preparation of complex macromolecular architectures containing polyamine segments, which were not accessible before.
Highlights
Linear polyamines, especially polyethylen- or propylenimine, would be ideal building blocks for macromolecular architectures for pH-responsive or metal-chelatingmaterials
Living anionic polymerization (LAP) is the superior method when it comes to the synthesis of well-defined polymers with low dispersity and complex architectures
The free polyamines are only obtained, after removal of the sulfonamides under typically harsh conditions, which potentially resulted in the scission of the main chain and incomplete desulfonylation or by using toxic solvents, such as hexamethylphosphoramide (HMPA).[3]
Summary
Especially polyethylen- or propylenimine, would be ideal building blocks for macromolecular architectures for pH-responsive or metal-chelating (nano)materials. To date, only a very limited number of polymers with well-defined polyamine segments have been reported.[1] Living anionic polymerization (LAP) is the superior method when it comes to the synthesis of well-defined polymers with low dispersity and complex architectures.
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