Superbase-enabled anionic polymerization of poly(alkyl cyanoacrylate)s:achieving well-defined structures and controlled molar masses

Poly(alkyl cyanoacrylate)s (PACAs) find extensive use as adhesives in engineering and medicine. However, their high reactivity often leads to wide molar mass dispersity and uncontrolled chain-end functionalities. Achieving precise polymer structures is crucial, particularly for medical applications to prevent oligomer toxicity. The conventional anionic polymerization of cyanoacrylates initiated by water results in high molar mass dispersities (Ð) and low end-group functionalities. Nonetheless, under specific conditions, anionic polymerization holds the potential for controlling the molar mass and Ð of PACAs. Here, we demonstrate the synthesis of well-defined PACAs by employing minute quantities (1%) of superbases to activate a functional thiophenol (PhSH) initiator. This strategy enables the attainment of adjustable molecular weights (Mn &gt; 20 kg mol−1) and moderate dispersities (Ð &lt; 1.4) for homopolymers and block copolymers. The selective initiation by thiophenol is confirmed through 1H DOSY NMR analysis. Furthermore, the controlled homo- and copolymerization of ACA derivatives highlights the remarkable performance of the superbase in conjunction with PhSH.</p

Ruthenocenyl Glycidyl Ether: A Ruthenium-Containing Epoxide for Anionic Polymerization

Ruthenocenyl glycidyl ether (rcGE) is a novel monomer for the anionic polymerization and copolymerization with ethylene oxide to water-soluble, thermo-, and redox-responsive organometallic poly­(ethylene glycol)­s (PEGs). The polymers exhibit adjustable molecular weights, comonomer ratios, and narrow molecular weight distributions (typically <i>M</i>_w/<i>M</i>_n < 1.2). Real-time ¹H NMR copolymerization kinetics prove random incorporation of rcGE into the polyether backbone in analogy to its ferrocene analog. The rcGE-<i>co</i>-EO copolymers are water-soluble with a lower critical solution temperature, depending on the rcGE content. Terpolymerization of ferrocenyl glycidyl ether, ethylene oxide, and rcGE produces the first random PEG derivatives with multiple redox response. Ruthenocenyl glycidyl ether broadens the field of organometallics, especially ruthenium-containing polymers, and these copolymers might find applications in catalysis, as redox-active surfactants, or as staining reagents in electron microscopy

Selective Initiation from Unprotected Aminoalcohols for the N -Heterocyclic Carbene-Organocatalyzed Ring-Opening Polymerization of 2-Methyl- N- tosyl Aziridine: Telechelic and Block Copolymer Synthesis

International audienc

Microwave-Assisted Desulfonylation of Polysulfonamides toward Polypropylenimine

Linear polyethylenimine (L-PEI) has been the gold standard for gene delivery and is typically prepared by hydrolysis from poly­(2-oxazoline)­s. Recently, also the anionic polymerization of activated aziridines was reported as a potential pathway toward linear and well-defined polyamines. However, only sulfonamide-activated aziridines so far undergo the living anionic polymerization and their desulfonylation was only reported scarcely. This is mainly due to the relatively high stability of the sulfonamides and the drastic change in solubility during the desulfonylation. Herein, we investigated the desulfonylation of such poly­(aziridine)­s prepared from tosylated or mesylated propyleneimine to afford linear polypropylenimine (L-PPI) as an alternative to L-PEI. Different desulfonylation strategies for tosylated (Ts) and mesylated (Ms) PPI were studied. The reductive cleavage of the sulfonamide with sodium bis­(2-methoxy ethoxy) aluminum hydride yielded 80% of deprotected amine groups. Quantitative conversion to L-PPI was obtained, when the tosylated PPI was hydrolyzed under acidic conditions with <i>p</i>TsOH under microwave (MW) irradiation. The same treatment removed 90% of the mesyl groups from the mesylated PPI analog. The MW-assisted acidic hydrolysis represents a fast, inexpensive and easy approach in comparison to other methods, where complex reaction conditions and tedious purifications are major drawbacks, however some chain scission may occur. The high purity of the obtained products, in combination with the versatility of the activated aziridine chemistry, demonstrate many advantages of our strategy, especially for future biomedical implementations

Alcohol- and Water-Tolerant Living Anionic Polymerization of Aziridines

International audienc

Selective Initiation from Unprotected Aminoalcohols for the <i>N</i>‑Heterocyclic Carbene-Organocatalyzed Ring-Opening Polymerization of 2‑Methyl-<i>N-</i>tosyl Aziridine: Telechelic and Block Copolymer Synthesis

Commercial aminoalcohols, namely, 2-(methyl amino)­ethanol (<b>1</b>) and diethanolamine (<b>2</b>), are investigated as direct initiators, i.e., with no need of protection of the hydroxyl groups, for the <i>N</i>-heterocyclic carbene-organocatalyzed ring-opening polymerization (NHC-OROP) of 2-methyl-<i>N</i>-<i>p</i>-toluenesulfonyl aziridine. NHC-OROP’s are performed at 50 °C in tetrahydrofuran, in the presence of 1,3-bis­(isopropyl)-4,5­(dimethyl)­imidazol-2-ylidene (^Me5-IPr) as organocatalyst. Thus, nonprotected and nonactivated aminoalcohol initiators <b>1</b> and <b>2</b> provide a direct access to metal-free α-hydroxy-ω-amino- and α,α′-bis-hydroxy-ω-amino telechelics on the basis of polyaziridine (PAz), respectively. Excellent control over molar masses, narrow dispersities (<i><i>Đ</i></i> ≤ 1.20), and high chain-end fidelity are evidenced by combined analyses, including NMR spectroscopy, size exclusion chromatography, and MALDI ToF mass spectrometry. The amino-initiated NHC-OROP is therefore tolerant to the presence of nonprotected hydroxyl group(s). The as-obtained hydroxyl-ended PAz can be further derivatized in reaction with phenyl isocyanate, highlighting the accessibility of the hydroxyl groups in α-position. Moreover, block copolymer synthesis can be readily achieved by sequential NHC-OROP of 2-methyl-<i>N</i>-<i>p</i>-toluenesulfonyl aziridine and l-lactide, from <b>1</b> used in this case as a double-headed initiator. Remarkably, each of the two NHC-OROP steps proves highly chemoselective, with PAz and poly­(l-lactide) (PLLA) segments being grown from the secondary amino- and the primary hydroxy- function, respectively. In this way, a well-defined PAz-<i>b</i>-PLLA diblock copolymer is synthesized in the presence of the same ^Me5-IPr organocatalyst, i.e., following a completely metal-free strategy

Alcohol- and Water-Tolerant Living Anionic Polymerization of Aziridines

Living anionic polymerization gives access to well-defined polymers, but it demands strict purification of reagents and solvents. This work presents the azaanionic polymerization (AAROP) of aziridines as a robust living polymerization technique, with the ease of controlled radical polymerizations. AAROP does not require inert atmosphere and remains living in the presence of large amounts of water or alcohols. Mesyl-, tosyl-, or brosyl-activated aziridines were polymerized with up to 100-fold excess of a protic impurity with respect to the initiator and still being active for chain extension. This allowed the preparation of polyols by anionic polymerization without protective groups, as only minor initiation occurred from the alcohols. The tolerance toward protic additives lies in the electron-withdrawing effect of the activating groups, decreasing the basicity of the propagating species, while maintaining a strong nucleophilic character. In this way, competing alcohols and water are only slightly involved in the polymerization, making living anionic polymerization an easy-to-conduct technique to well-defined polyamides and -amines