controlled-photoredox-ring-opening-polymerization-o-carboxyanhydrides

Controlled Photoredox Ring-Opening Polymerization of <em>O</em>-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

Virginia Polytechnic Institute and State University

Recently O-carboxyanhydrides (OCAs) have emerged as a class of viable monomers which can undergo ring-opening polymerization (ROP) to prepare poly(α-hydroxyalkanoic acid) with functional groups that are typically difficult to achieve by ROP of lactones. Organocatalysts for the ROP of OCAs, such as dimethylaminopyridine (DMAP), may induce undesired epimerization of the α-carbon atom in polyesters resulting in the loss of isotacticity. Herein, we report the use of (BDI-IE)Zn(OCH(CH3 )COOCH3 ) ((BDI)Zn-1, (BDI-IE)=2-((2,6-diethylphenyl)amino)-4-((2,6-diisopropylphenyl)imino)-2-pentene), for the controlled ROP of various OCAs without epimerization. Both homopolymers and block copolymers with controlled molecular weights, narrow molecular weight distributions, and isotactic backbones can be readily synthesized. (BDI)Zn-1 also enables controlled copolymerization of OCAs and lactide, facilitating the synthesis of block copolymers potentially useful for various biomedical applications. Preliminary mechanistic studies suggest that the monomer/dimer equilibrium of the zinc catalyst influences the ROP of OCAs, with the monomeric (BDI)Zn-1 possessing superior catalytic activity for the initiation of ROP in comparison to the dimeric (BDI)Zn complex.

Controlled Ring-Opening Polymerization of O-Carboxyanhydrides Using a β-Diiminate Zinc Catalyst.

Poly(α-hydroxy acids) are important biodegradable polymers with wide applications. Attempts to synthesize them from O-carboxyanhydrides with pendant functional groups by various methods, including methods involving organocatalysts or organometallics, have been plagued by uncontrolled polymerization, including epimerization for some monomers, which hampers the preparation of stereoregular high-molecular-weight polymers. Herein we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic polyesters with expected molecular weights (>140 kDa) and narrow molecular weight distributions (Mw/Mn < 1.1). Mechanistic studies indicate that the use of a low temperature (-20 °C) and photoredox Ni/Ir catalysis synergistically accelerates ring-opening and decarboxylation of the monomer for chain propagation while avoiding the formation of the undesired Ni-carbonyl complex.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides.

Near-infrared light has significant advantages for light-triggered drug delivery systems within deep tissues. The use of inorganic nanomaterials raises concern over their long-term in vivo toxicities. Here we will highlight emerging near-infrared light-triggered drug delivery using organic nanomaterials, as well as new photocleavage reactions mediated by near-infrared light.

Article	Year
Controlled Ring-Opening Polymerization of O-Carboxyanhydrides Using a β-Diiminate Zinc Catalyst. Angewandte Chemie (International ed. in English)\| PubMed ID: 27634170	2016
Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides. Journal of the American Chemical Society\| PubMed ID: 28397499	2017
Emerging strategies in near-infrared light triggered drug delivery using organic nanomaterials. Biomaterials science\| PubMed ID: 28589987	2017

Rong Tong

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