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Special Issue "Lewis Pair Polymerization for New Reactivity and Structure in Polymer Synthesis"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (15 January 2018)

Special Issue Editors

Guest Editor
Prof. Dr. Miao Hong

State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
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Interests: organometallic and organic catalysis for efficient and controlled polymerization; sustainable polymers, helical chiral polymers and functional polyolefins
Guest Editor
Dr. Jiawei Chen

Department of Chemistry, Columbia University, 3000 Broadway, New York, NY 10027, USA
E-Mail
Interests: Lewis acid-mediated catalysis; frustrated Lewis pair chemistry; metal hydride chemistry; hydrosilylation; Lewis pair polymerization
Guest Editor
Prof. Dr. Eugene Y.-X. Chen

Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, USA
Website | E-Mail
Interests: recyclable & renewable polymers; metal-mediated precision (stereoselective, chemoselective, and living) polymer synthesis; Lewis pair polymerization; organopolymerization; biomass conversion

Special Issue Information

Dear Colleagues,

The last decade has witnessed tremendous progress in the emerging frustrated Lewis pair (FLP) chemistry, since the seminal discovery of heterolytic cleavage of dihydrogen by sterically encumbered Lewis acid/base pairs. Thanks to the vigorous and sustained research carried out in this area, FLP chemistry has proved to be a powerful and versatile transition-metal-free strategy for small molecule activations and related catalytic transformations. Subsequent efforts have been devoted to the understanding of fundamental aspects of FLP chemistry and exploiting the reactivity and cooperativity of Lewis pairs to new areas such as polymer synthesis. In this context, the concept of Lewis pair polymerization (LPP)—which utilizes an FLP, a classical Lewis adduct (CLA), or an interacting Lewis pair at the intermediacy between FLP and CLA states—to achieve cooperative monomer activation and chain initiation and/or propagation has been developed to synthesize various types of polymers. The seemingly unlimited tunability of the steric effects and electronic properties of Lewis acids and bases, and therefore the interactions between the resulting Lewis pairs, allows the development of a variety of initiator or catalyst systems that are capable of promoting different types of polymerizations, such as addition polymerization of polar and non-polar vinyl monomers, and ring opening (co)polymerization of heterocyclic monomers. Living and chemoselective LPP processes have also been recently uncovered.

The goal of this special issue is to collect and disseminate some of the significant contributions in the area of polymer synthesis recently enabled by LPP, emphasizing the development of new polymerization reactions rendered by new Lewis pair catalyst/initiator systems, exploration of monomer scopes, and synthesis of polymers with controlled or unique structures. Hence, we cordially invite you to submit your valuable contributions to this special issue on the LPP topic that interfaces with main-group, organometallic, and polymer chemistry, as well as catalytic and green chemistry.

Prof. Dr. Miao Hong
Dr. Jiawei Chen
Prof. Dr. Eugene Y.-X. Chen
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Lewis pair polymerization
  • frustrated Lewis pair
  • interacting Lewis pair
  • classical Lewis adduct
  • polymerization catalysis
  • polymer synthesis
  • green chemistry

Published Papers (11 papers)

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Editorial

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Open AccessEditorial Lewis Pair Polymerization for New Reactivity and Structure in Polymer Synthesis
Molecules 2018, 23(4), 915; https://doi.org/10.3390/molecules23040915
Received: 8 April 2018 / Revised: 9 April 2018 / Accepted: 12 April 2018 / Published: 16 April 2018
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Research

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Open AccessFeature PaperArticle Zn(OAc)2-Catalyzing Ring-Opening Polymerization of N-Carboxyanhydrides for the Synthesis of Well-Defined Polypeptides
Molecules 2018, 23(4), 760; https://doi.org/10.3390/molecules23040760
Received: 13 March 2018 / Revised: 23 March 2018 / Accepted: 23 March 2018 / Published: 26 March 2018
Cited by 1 | PDF Full-text (2768 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Despite notable progress, the fabrication of well-defined polypeptides via controlled ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) using convenient catalysts under mild conditions in a relatively short polymerization time is still challenging. Herein, an easily obtained catalyst system composed of zinc
[...] Read more.
Despite notable progress, the fabrication of well-defined polypeptides via controlled ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) using convenient catalysts under mild conditions in a relatively short polymerization time is still challenging. Herein, an easily obtained catalyst system composed of zinc acetate and aniline was explored to mediate the fast ROP of γ-benzyl-l-glutamate-N-carboxyanhydride (BLG-NCA) monomer, to produce poly(γ-benzyl-l-glutamates) (PBLGs) with controllable molecular weights and narrow dispersity. Considering the excellent cooperative action of zinc acetate and a broad scope of aniline derivatives with different functional groups to control ROP of BLG-NCA, this method may offer a useful platform enabling the rapid generation of end-functionalized PBLG and block copolymers for numerous biomedical applications. Full article
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Open AccessArticle Silyl Ketene Acetals/B(C6F5)3 Lewis Pair-Catalyzed Living Group Transfer Polymerization of Renewable Cyclic Acrylic Monomers
Molecules 2018, 23(3), 665; https://doi.org/10.3390/molecules23030665
Received: 30 January 2018 / Revised: 11 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
Cited by 1 | PDF Full-text (3151 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This work reveals the silyl ketene acetal (SKA)/B(C6F5)3 Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in
[...] Read more.
This work reveals the silyl ketene acetal (SKA)/B(C6F5)3 Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in situ NMR monitored reaction of SKA with B(C6F5)3 indicated the formation of Frustrated Lewis Pairs (FLPs), although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C6F5)3-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C6F5)3-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C6F5)3 is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). Moreover, using this method, we have successfully synthesized well-defined PMMBL-b-PMBL, PMMBL-b-PMBL-b-PMMBL and random copolymers with the predicated molecular weights (Mn) and narrow molecular weight distribution (MWD). Full article
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Open AccessFeature PaperArticle Tandem Lewis Pair Polymerization and Organocatalytic Ring-Opening Polymerization for Synthesizing Block and Brush Copolymers
Molecules 2018, 23(2), 468; https://doi.org/10.3390/molecules23020468
Received: 25 January 2018 / Revised: 18 February 2018 / Accepted: 18 February 2018 / Published: 21 February 2018
Cited by 1 | PDF Full-text (2611 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Lewis pair polymerization is a powerful method for preparing soluble polymers bearing pendant active vinyl groups by directly polymerizing dissymmetric divinyl polar monomers. Herein, we present a strategy for synthesizing block and brush copolymers via tandem Lewis pair polymerization of methacrylates, “thiol-ene” click
[...] Read more.
Lewis pair polymerization is a powerful method for preparing soluble polymers bearing pendant active vinyl groups by directly polymerizing dissymmetric divinyl polar monomers. Herein, we present a strategy for synthesizing block and brush copolymers via tandem Lewis pair polymerization of methacrylates, “thiol-ene” click reaction and organocatalytic ring-opening polymerization of lactide. Full article
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Open AccessFeature PaperArticle Controlled and Efficient Polymerization of Conjugated Polar Alkenes by Lewis Pairs Based on Sterically Hindered Aryloxide-Substituted Alkylaluminum
Molecules 2018, 23(2), 442; https://doi.org/10.3390/molecules23020442
Received: 30 January 2018 / Revised: 12 February 2018 / Accepted: 14 February 2018 / Published: 17 February 2018
Cited by 1 | PDF Full-text (1072 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Reported herein is the development of an effective strategy for controlled and efficient Lewis pair polymerization of conjugated polar alkenes, including methyl methacrylate (MMA), n-butyl methacrylate (nBuMA), and γ-methyl-α-methylene-γ-butyrolactone (γMMBL), by the utilization of sterically encumbered Al(BHT)2Me (BHT:
[...] Read more.
Reported herein is the development of an effective strategy for controlled and efficient Lewis pair polymerization of conjugated polar alkenes, including methyl methacrylate (MMA), n-butyl methacrylate (nBuMA), and γ-methyl-α-methylene-γ-butyrolactone (γMMBL), by the utilization of sterically encumbered Al(BHT)2Me (BHT: 2,6-di-tert-butyl-4-methylphenol) as a Lewis acid that shuts down intramolecular backbiting termination. In combination with a selected N-heterocyclic carbene (NHC) as a Lewis base, the polymerization of MMA exhibited activity up to 3000 h−1 TOF and an acceptable initiation efficiency of 60.6%, producing polymers with high molecular weight (Mn up to 130 kg/mol) and extremely narrow dispersity (Đ = 1.06~1.13). This controlled polymerization with a living characteristic has been evidenced by chain-extension experiments and chain-end analysis, and enabled the synthesis of well-defined diblock copolymers. Full article
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Open AccessFeature PaperArticle The Lewis Pair Polymerization of Lactones Using Metal Halides and N-Heterocyclic Olefins: Theoretical Insights
Molecules 2018, 23(2), 432; https://doi.org/10.3390/molecules23020432
Received: 15 January 2018 / Revised: 12 February 2018 / Accepted: 12 February 2018 / Published: 15 February 2018
Cited by 1 | PDF Full-text (1376 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Lewis pair polymerization employing N-Heterocyclic olefins (NHOs) and simple metal halides as co-catalysts has emerged as a useful tool to polymerize diverse lactones. To elucidate some of the mechanistic aspects that remain unclear to date and to better understand the impact of
[...] Read more.
Lewis pair polymerization employing N-Heterocyclic olefins (NHOs) and simple metal halides as co-catalysts has emerged as a useful tool to polymerize diverse lactones. To elucidate some of the mechanistic aspects that remain unclear to date and to better understand the impact of the metal species, computational methods have been applied. Several key aspects have been considered: (1) the formation of NHO-metal halide adducts has been evaluated for eight different NHOs and three different Lewis acids, (2) the coordination of four lactones to MgCl2 was studied and (3) the deprotonation of an initiator (butanol) was investigated in the presence and absence of metal halide for one specific Lewis pair. It was found that the propensity for adduct formation can be influenced, perhaps even designed, by varying both organic and metallic components. Apart from the NHO backbone, the substituents on the exocyclic, olefinic carbon have emerged as interesting tuning site. The tendency to form adducts is ZnCl2 > MgCl2 > LiCl. If lactones coordinate to MgCl2, the most likely binding mode is via the carbonyl oxygen. A chelating coordination cannot be ruled out and seems to gain importance upon increasing ring-size of the lactone. For a representative NHO, it is demonstrated that in a metal-free setting an initiating alcohol cannot be deprotonated, while in the presence of MgCl2 the same process is exothermic with a low barrier. Full article
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Open AccessFeature PaperArticle Polysiloxane/Polystyrene Thermo-Responsive and Self-Healing Polymer Network via Lewis Acid-Lewis Base Pair Formation
Molecules 2018, 23(2), 405; https://doi.org/10.3390/molecules23020405
Received: 28 January 2018 / Revised: 6 February 2018 / Accepted: 8 February 2018 / Published: 13 February 2018
Cited by 1 | PDF Full-text (3276 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The use of thermo-reversible Lewis Pair (LP) interactions in the formation of transient polymer networks is still greatly underexplored. In this work, we describe the synthesis and characterization of polydimethylsiloxane/polystyrene (PDMS/PS) blends that form dynamic Lewis acid-Lewis base adducts resulting in reversible crosslinks.
[...] Read more.
The use of thermo-reversible Lewis Pair (LP) interactions in the formation of transient polymer networks is still greatly underexplored. In this work, we describe the synthesis and characterization of polydimethylsiloxane/polystyrene (PDMS/PS) blends that form dynamic Lewis acid-Lewis base adducts resulting in reversible crosslinks. Linear PS containing 10 mol % of di-2-thienylboryl pendant groups randomly distributed was obtained in a two-step one-pot functionalization reaction from silyl-functionalized PS, while ditelechelic PDMS with pyridyl groups at the chain-termini was directly obtained via thiol-ene “click” chemistry from commercially available vinyl-terminated PDMS. The resulting soft gels, formed after mixing solutions containing the PDMS and PS polymers, behave at room temperature as elastomeric solid-like materials with very high viscosity (47,300 Pa·s). We applied rheological measurements to study the thermal and time dependence of the viscoelastic moduli, and also assessed the reprocessability and self-healing behavior of the dry gel. Full article
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Open AccessFeature PaperArticle Chemoselective Polymerization of Polar Divinyl Monomers with Rare-Earth/Phosphine Lewis Pairs
Molecules 2018, 23(2), 360; https://doi.org/10.3390/molecules23020360
Received: 6 January 2018 / Revised: 1 February 2018 / Accepted: 6 February 2018 / Published: 8 February 2018
Cited by 1 | PDF Full-text (1145 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This work reports the chemoselective polymerization of polar divinyl monomers, including allyl methacrylate (AMA), vinyl methacrylate (VMA), and 4-vinylbenzyl methacrylate (VBMA), by using simple Lewis pairs comprised of homoleptic rare-earth (RE) aryloxide complexes RE(OAr)3 (RE = Sc (1), Y (
[...] Read more.
This work reports the chemoselective polymerization of polar divinyl monomers, including allyl methacrylate (AMA), vinyl methacrylate (VMA), and 4-vinylbenzyl methacrylate (VBMA), by using simple Lewis pairs comprised of homoleptic rare-earth (RE) aryloxide complexes RE(OAr)3 (RE = Sc (1), Y (2), Sm (3), La (4), Ar = 2,6-tBu2C6H3) and phosphines PR3 (R = Ph, Cy, Et, Me). Catalytic activities of polymerizations relied heavily upon the cooperation of Lewis acid and Lewis base components. The produced polymers were soluble in common organic solvents and often had a narrow molecular weight distribution. A highly syndiotactic poly(allyl methacrylate) (PAMA) with rr ~88% could be obtained by the scandium complex 1/PEt3 pair at −30 °C. In the case of poly(4-vinylbenzyl methacrylate) (PVBMA), it could be post-functionalized with PhCH2SH. Mechanistic study, including the isolation of the zwitterionic active species and the end-group analysis, revealed that the frustrated Lewis pair (FLP)-type addition was the initiating step in the polymerization. Full article
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Open AccessArticle Highly Efficient One-Pot Synthesis of COS-Based Block Copolymers by Using Organic Lewis Pairs
Molecules 2018, 23(2), 298; https://doi.org/10.3390/molecules23020298
Received: 14 January 2018 / Revised: 28 January 2018 / Accepted: 30 January 2018 / Published: 31 January 2018
Cited by 2 | PDF Full-text (1126 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A one-pot synthesis of block copolymer with regioregular poly(monothiocarbonate) block is described via metal-free catalysis. Lewis bases such as guanidine, quaternary onium salts, and Lewis acid triethyl borane (TEB) were equivalently combined and used as the catalysts. By using polyethylene glycol (PEG) as
[...] Read more.
A one-pot synthesis of block copolymer with regioregular poly(monothiocarbonate) block is described via metal-free catalysis. Lewis bases such as guanidine, quaternary onium salts, and Lewis acid triethyl borane (TEB) were equivalently combined and used as the catalysts. By using polyethylene glycol (PEG) as the macromolecular chain transfer agent (CTA), narrow polydispersity block copolymers were obtained from the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO). The block copolymers had a poly(monothiocarbonate) block with perfect alternating degree and regioregularity. Unexpectedly, the addition of CTA to COS/PO copolymerization system could dramatically improve the turnover frequency (TOF) of PO (up to 240 h−1), higher than that of the copolymerization without CTA. In addition, the conversion of CTA could be up to 100% in most cases, as revealed by 1H NMR spectra. Of consequence, the number-average molecular weights (Mns) of the resultant block copolymers could be regulated by varying the feed ratio of CTA to PO. Oxygen-sulfur exchange reaction (O/S ER), which can generate randomly distributed thiocarbonate and carbonate units, was effectively suppressed in all of the cases in the presence of CTA, even at 80 °C. This work presents a versatile method for synthesizing sulfur-containing block copolymers through a metal-free route, providing an array of new block copolymers. Full article
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Open AccessFeature PaperArticle Brush Polymer of Donor-Accepter Dyads via Adduct Formation between Lewis Base Polymer Donor and All Carbon Lewis Acid Acceptor
Molecules 2017, 22(9), 1564; https://doi.org/10.3390/molecules22091564
Received: 10 August 2017 / Accepted: 10 September 2017 / Published: 18 September 2017
Cited by 1 | PDF Full-text (12400 KB) | HTML Full-text | XML Full-text
Abstract
A synthetic method that taps into the facile Lewis base (LB)→Lewis acid (LA) adduct forming reaction between the semiconducting polymeric LB and all carbon LA C60 for the construction of covalently linked donor-acceptor dyads and brush polymer of dyads is reported. The
[...] Read more.
A synthetic method that taps into the facile Lewis base (LB)→Lewis acid (LA) adduct forming reaction between the semiconducting polymeric LB and all carbon LA C60 for the construction of covalently linked donor-acceptor dyads and brush polymer of dyads is reported. The polymeric LB is built on poly(3-hexylthiophene) (P3HT) macromers containing either an alkyl or vinyl imidazolium end group that can be readily converted into the N-heterocyclic carbene (NHC) LB site, while the brush polymer architecture is conveniently constructed via radical polymerization of the macromer P3HT with the vinyl imidazolium chain end. Simply mixing of such donor polymeric LB with C60 rapidly creates linked P3HT-C60 dyads and brush polymer of dyads in which C60 is covalently linked to the NHC junction connecting the vinyl polymer main chain and the brush P3HT side chains. Thermal behaviors, electronic absorption and emission properties of the resulting P3HT-C60 dyads and brush polymer of dyads have been investigated. The results show that a change of the topology of the P3HT-C60 dyad from linear to brush architecture enhances the crystallinity and Tm of the P3HT domain and, along with other findings, they indicate that the brush polymer architecture of donor-acceptor domains provides a promising approach to improve performances of polymer-based solar cells. Full article
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Review

Jump to: Editorial, Research

Open AccessFeature PaperReview Lewis Pair Catalysts in the Polymerization of Lactide and Related Cyclic Esters
Molecules 2018, 23(1), 189; https://doi.org/10.3390/molecules23010189
Received: 28 December 2017 / Revised: 15 January 2018 / Accepted: 16 January 2018 / Published: 17 January 2018
Cited by 1 | PDF Full-text (2874 KB) | HTML Full-text | XML Full-text
Abstract
Polyesters, especially poly(lactide) (PLA), are used widely as biodegradable and biocompatible materials, yet their controllable synthesis, especially the stereoselective synthesis of polyesters, is still a challenge. Recently some excellent Lewis pair catalysts for ring-opening polymerization (ROP) of lactide and related cyclic esters have
[...] Read more.
Polyesters, especially poly(lactide) (PLA), are used widely as biodegradable and biocompatible materials, yet their controllable synthesis, especially the stereoselective synthesis of polyesters, is still a challenge. Recently some excellent Lewis pair catalysts for ring-opening polymerization (ROP) of lactide and related cyclic esters have emerged. This review article will highlight the key advances in the ROP catalyzed by Lewis pair compounds with the aim of encouraging the wider application of Lewis pair catalysts in the polymerization of lactide and related cyclic esters. Full article
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