Living/Controlled Polymerization of Renewable Lignin-Based Monomers by Lewis Pairs

It is a challenging task to replace the traditional petroleum-based monomers with the biorenewable monomers for polymer synthesis, as it can alleviate the energy and environmental crises. Lewis pairs (LP) composed of organophosphorus superbases and organoaluminum Lewis acid are employed to rapidly and quantitatively transform a series of biorenewable monomers derived from the lignin degradation products into polymers with predicted molecular weight (Mn up to 519 kg mol–1) and small Đ value (as low as 1.10). The livingness of the polymerization of lignin-based monomer by such LP system can be also verified by the following evidence, including a linear increase of polymer Mn vs monomer-to-initiator ratio and monomer conversion and high end-group fidelity as evidenced by successful chain extensions and synthesis of well-defined block copolymers. More impressively, the lignin-based copolymers with methyl ferulate exhibited fluorescence response under the irradiation of UV light at 365 nm, suggesting application potential of the lignin-based polymers in biological imaging, information storage, and anti-counterfeiting materials

Living Ring-Opening Polymerization of Lactones by <i>N</i>‑Heterocyclic Olefin/Al(C₆F₅)₃ Lewis Pairs: Structures of Intermediates, Kinetics, and Mechanism

The strong Lewis acid Al­(C6F5)3, in combination with a strong Lewis base N-heterocyclic olefin (NHO), cooperatively promotes the living ring-opening (co)­polymerization of lactones, represented by δ-valerolactone (δ-VL) and ε-caprolactone (ε-CL) in this study. Medium to high molecular weight linear (co)­polyesters (Mw up to 855 kg/mol) are achieved, and most of them exhibit narrow molecular weight distributions (Đ as low as 1.02). Detailed investigations into the structures of key reaction intermediates, kinetics, and polymer structures have led to a polymerization mechanism, in that initiation involves nucleophilic attack of the Al­(C6F5)3-activated monomer by NHO to form a structurally characterized zwitterionic, tetrahedral intermediate, followed by its ring-opening to generate active zwitterionic species. In the propagation cycle, this ring-opened zwitterionic species and its homologues attack the incoming monomer activated by Al­(C6F5)3 to generate the tetrahedral intermediate, followed by the rate-determining ring-opening step to regenerate the zwitterionic species that re-enters into the next chain propagation cycles. Owning to the living features and lack of transesterification side reactions possessed uniquely by this Lewis pair polymerization system, well-defined di- and triblock copolymers with narrow molecular weight distributions (Đ = 1.06–1.15) have been successfully synthesized using this method, regardless of the comonomer addition order

Living Ring-Opening Polymerization of Lactones by <i>N</i>‑Heterocyclic Olefin/Al(C₆F₅)₃ Lewis Pairs: Structures of Intermediates, Kinetics, and Mechanism

The strong Lewis acid Al­(C6F5)3, in combination with a strong Lewis base N-heterocyclic olefin (NHO), cooperatively promotes the living ring-opening (co)­polymerization of lactones, represented by δ-valerolactone (δ-VL) and ε-caprolactone (ε-CL) in this study. Medium to high molecular weight linear (co)­polyesters (Mw up to 855 kg/mol) are achieved, and most of them exhibit narrow molecular weight distributions (Đ as low as 1.02). Detailed investigations into the structures of key reaction intermediates, kinetics, and polymer structures have led to a polymerization mechanism, in that initiation involves nucleophilic attack of the Al­(C6F5)3-activated monomer by NHO to form a structurally characterized zwitterionic, tetrahedral intermediate, followed by its ring-opening to generate active zwitterionic species. In the propagation cycle, this ring-opened zwitterionic species and its homologues attack the incoming monomer activated by Al­(C6F5)3 to generate the tetrahedral intermediate, followed by the rate-determining ring-opening step to regenerate the zwitterionic species that re-enters into the next chain propagation cycles. Owning to the living features and lack of transesterification side reactions possessed uniquely by this Lewis pair polymerization system, well-defined di- and triblock copolymers with narrow molecular weight distributions (Đ = 1.06–1.15) have been successfully synthesized using this method, regardless of the comonomer addition order

Simply Prepared Dual-Initiating Bis-Phosphonium Ylide-Based Lewis Pairs for Efficient Synthesis of Alkyl (Meth)acrylates (Co)polymers

The development of simply prepared catalysts for efficient and controlled polymerization is an important research challenge in polymer chemistry. Here, six newly designed dual-initiating bis-phosphonium ylide Lewis bases (LBs) with different linker lengths were prepared in a one-step process. When combined with organoaluminum, these LBs enable rapid and living polymerization of five alkyl (meth)acrylates, including methyl methacrylate (MMA), ethyl methacrylate (EMA), benzyl methacrylate (BnMA), n-butyl acrylate (nBA), and 2-ethylhexyl acrylate (EHA). Consequently, polymers with predictable molecular weights (Mn up to 155.1 kg/mol) and small Đ values (as low as 1.08) can be synthesized. By integrating the unique compounded sequence control (CSC) strategy of Lewis pair polymerization (LPP) and dual-initiating character of these bis-phosphonium ylide LBs, undecablock copolymers of different monomers were prepared through three sequential monomer mixture feeding while maintaining excellent controllability over polymer structures as demonstrated by gel permeation chromatography (GPC) and diffusion ordered spectroscopy (DOSY) analyses. Furthermore, a series of all-acrylic-based thermoplastic elastomers (TPEs) with different hard and soft segments were also synthesized in one-step, and the copolymer structures and glass transition temperature (Tg) effects on the mechanical properties of the TPEs were investigated. Hence, the aforementioned outcomes underscore the efficiency and robust capability of our newly developed bis-phosphonium ylide-based LPP strategy in polymer synthesis

Living Ring-Opening Polymerization of Lactones by <i>N</i>‑Heterocyclic Olefin/Al(C₆F₅)₃ Lewis Pairs: Structures of Intermediates, Kinetics, and Mechanism

The strong Lewis acid Al­(C₆F₅)₃, in combination with a strong Lewis base <i>N</i>-heterocyclic olefin (NHO), cooperatively promotes the living ring-opening (co)­polymerization of lactones, represented by δ-valerolactone (δ-VL) and ε-caprolactone (ε-CL) in this study. Medium to high molecular weight linear (co)­polyesters (<i>M</i>_w up to 855 kg/mol) are achieved, and most of them exhibit narrow molecular weight distributions (<i>Đ</i> as low as 1.02). Detailed investigations into the structures of key reaction intermediates, kinetics, and polymer structures have led to a polymerization mechanism, in that initiation involves nucleophilic attack of the Al­(C₆F₅)₃-activated monomer by NHO to form a structurally characterized zwitterionic, tetrahedral intermediate, followed by its ring-opening to generate active zwitterionic species. In the propagation cycle, this ring-opened zwitterionic species and its homologues attack the incoming monomer activated by Al­(C₆F₅)₃ to generate the tetrahedral intermediate, followed by the rate-determining ring-opening step to regenerate the zwitterionic species that re-enters into the next chain propagation cycles. Owning to the living features and lack of transesterification side reactions possessed uniquely by this Lewis pair polymerization system, well-defined di- and triblock copolymers with narrow molecular weight distributions (<i>Đ</i> = 1.06–1.15) have been successfully synthesized using this method, regardless of the comonomer addition order

Living Polymerization of Conjugated Polar Alkenes Catalyzed by <i>N</i>‑Heterocyclic Olefin-Based Frustrated Lewis Pairs

The living polymerization of conjugated polar alkenes such as methacrylates by a noninteracting, authentic frustrated Lewis pair (FLP) has remained elusive ever since the report on FLP-promoted polymerization in 2010. Here we report that the polymerization of alkyl methacrylates by a FLP system based on a strongly nucleophilic <i>N</i>-heterocyclic olefin (NHO) Lewis base and sterically encumbered but modestly strong Lewis acid MeAl­(4-Me-2,6-^<i>t</i>Bu₂-C₆H₂O)₂ is not only rapid but also living. This living polymerization was indicated by the formation of a linear, living chain, capped with NHO/H chain ends, without backbiting-derived cyclic chain ends. The true livingness of this FLP-promoted polymerization has been unequivocally verified by five lines of evidence, including the predicted polymer number-average molecular weight (<i>M</i>_n, up to 351 kg·mol^–1) coupled with low dispersity (<i>Đ</i> = 1.05) values; obtained high to quantitative initiation efficiencies; an observed linear increase of polymer <i>M</i>_n vs monomer conversion and the monomer-to-initiator ratio; found precision in multiple chain extensions; and formed well-defined diblock and ABA triblock copolymers with narrow molecular weight distributions (<i>Đ</i> = 1.09–1.13), regardless of the comonomer addition order