Valence‐variable Catalysts for Redox‐controlled Switchable Ring‐opening Polymerization

Abstract

As a representative class of sustainable polymer materials, biodegradable polymers have attracted increasing interest in recent years. Despite significant advance of related polymerization techniques, realizing high sequence‐control and easy‐handling in ring‐opening (co)polymerizations still remains a central challenge. To this end, a promising solution is the development of valence‐variable metal‐based catalysts for redox‐induced switchable polymerization of cyclic esters, cyclic ethers, epoxides, and CO2. Through a valence‐determined electron effect, the switch between different catalytically active states as well as dormant state contributes to convenient formation of polymer products with desired microstructures and various practical performances. This redox‐controlled switchable strategy for controlled synthesis of polymers is overviewed in this Review with a focus on potential applications and challenges for further studies.

Sustainable, Recyclable, and Bench-Stable Catalytic System for Synthesis of Poly(ester-b-carbonate)

“…The development of novel catalyst systems, e.g., metal-based catalysts, Lewis pairs, and organocatalysts, has made great strides in the aforementioned designing of sustainable polymers, which are favorable for approaching the synthesis of desirable polymers. ,,− Pioneering work about metal-based catalysts from the groups of Coates, Nozaki, and Williams, amongst others, demonstrated the significant potential of dinuclear catalysts in CO 2 /epoxide ROCOP, the key of these proposed mechanistic hypotheses being that two metal centers at optimum distances could coordinate and catalyze the copolymerization with significantly enhanced activity. ,,,,− Furthermore, we and other groups have reported switchable polymerization, some of which showed better performances in tandem polymerization strategy. ,,,,, In terms of nonmetal catalysts, Li and other researchers reported multiblock poly­(ester- b -carbonate) copolymers through the orthogonal copolymerization of epoxides/CO 2 and ROCOP of CHO/PA with the help of Lewis pairs. − Meanwhile, similar Lewis pair also were reported to successfully synthesize multiblock copolymers by sequential ROCOP of cyclohexene oxide (CHO)/PA and ROP of LLA. , …”

N-(2-(Diphenylphosphino)ethyl)-2-alkyl-5,6,7,8-tetrahydro-quinolin-8-amines iron(ii) complexes: structural diversity and the ring opening polymerization of ε-caprolactone

“… 8 To develop non-toxic catalysts, the most abundant transition-metal iron-based catalysts have been found to be potential catalysts for the ROP of cyclic esters 9,10 and are biocompatible. 11–13 Interestingly, valence-variable iron catalysts have been found in redox-controlled ROP, 14 iron salts, such as FeCl 3 , Fe 2 O 3 , and FeS, which displayed low efficiency toward ROP of lactides or ε-caprolactone (ε-CL) in bulk polymerization; 15–17 in contrast, the FeCl 3 hydrate salts are efficient catalysts toward the bulk polymerization of ε-CL, δ-valerolactone (δ-VL), and β-butyrolactone (β-BL). 18 Employing initiators (water, isopropyl alcohol, benzyl alcohol, and 2-allyl phenol), commercial iron( iii ) salts, such as FeCl 3 , FeBr 3 , and perchlorate, were found to be efficient for the ROP of ε-CL.…”