Archive for August, 2019

Synthesizing Polymers Using CO2

Ring-opening polymerizations produce commercial polymeric materials including epoxy resins, but they usually liberate small molecules such as the greenhouse gas, CO2. In the context of climate change, it is urgent to reduce CO2 emissions. Recently, a group of UK researchers led by Prof. Charlotte K. Williams at the University of Oxford developed a step-growth polymerization method that self-consumed CO2. The work has been published in a recent issue of Chemical Communications.

The synthesis involved two catalytic cycles (Figure 1). The first cycle polymerized L-lactide-O-carboxyanhydride into poly(L-lactide acid) (PLLA) via a ring-opening polymerization and released one CO2 molecule per polymer repeat unit. In the second cycle, epoxide molecules (cyclohexeneoxide) combined with the CO2 generated in the first step and grew into poly(cyclohexene carbonate) (PCHC) from the terminal ends of the PLLA chains. A di-zinc-alkoxide compound catalyzed both cycles and coupled the two processes together. The product is PLLA-b-PCHC block copolymers, which are composed of PLLA and PCHC covalently tethered together.

Figure 1. The two catalytic cycles are joined by a zinc-based catalyst, [LZn2(OAc)2]. The CO2 gas produced in the first step serves as a reactant in the second step. OCA: O-carboxyanhydride; ROP: ring-opening polymerization; CHO: cyclohexeneoxide; ROCOP: ring-opening copolymerization.

The two reactions resulted in block copolymers with few byproducts. In-situ 1H NMR revealed that the reactants in the first step (LLAOCA) were rapidly consumed during the first four hours (Step I, Figure 2a), and the concentration of PLLA increased notably. The concentration of PCHC only markedly increased after the concentration of PLLA saturated (Step II, Figure 2a). The byproduct of the second step, trans-cyclohexene carbonate, exhibited consistently low concentrations. The pronounced single peak in each size-exclusion chromatogram of the corresponding product confirmed the presence of block copolymers, instead of polymer mixtures (Figure 2b). Although the authors did not fully elucidate the origin of the excellent selectivity towards the block copolymer, they speculated that the change in CO2 partial pressure played a role. Significantly, nearly all CO2 molecules were consumed in the second step, with 91% incorporated into the block copolymer, and 9% converted to the byproduct.

Figure 2. (a) The evolution of the concentrations of PLLA, PCHC, and trans-CHC (the byproduct of the second step) with reaction time. (b) Size-exclusion chromatograms of the products at different reaction times. Mn: number-average molecular weight; Đ: polydispersity.

The authors are investigating the detailed polymerization mechanism, as well as identifying new catalysts to expand the polymerization scheme to other polymers.

 

To find out more, please read:

Waste Not, Want Not: CO2 (Re)cycling into Block Copolymers

Sumesh K. Raman, Robert Raja, Polly L. Arnold, Matthew G. Davidson, and Charlotte K. Williams

Chem. Commun., 2019, 55, 7315-7318

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Chemical Communications: Editor’s Choice

Be sure to read our Editor’s Choice articles as chosen by Associate Editors Prof. Jonathan Steed & Prof. Jonathan Sessler!

All articles are free-to-access until 31st August and can be found in our online Editor’s Choice web-collection!

Planar rings in nano-Saturns and related complexes” by Steven M. Bachrach, as chosen by Jonathan Steed:

“This paper lays down the gauntlet to synthetic chemists! The image of a nano-Saturn is immediately eye-catching and scales up molecular host guest chemistry to the multi-nanometre scale. This creative theoretical paper establishes that ortho-nitrogen substitution in aryl macrocycles creates large planar or ribbon structures and then goes on to show that these discs or rings can combine with other nanostructures to construct complexes with interesting shapes. Given the huge interest generated by the mechanically interlocked structures underlying the 2016 Nobel prize in chemistry, these large-scale included systems are real food for thought and I am excited to see if they can be realised experimentally.”

Enhancing selectivity of cation exchange with anion receptors” by 

“These researchers have shown that by using a classic anion binding agent, namely a calix[4]pyrrole, it is possible to modulate the inherent selectivity of liquid-liquid cation extractants. Most current extraction-based separations rely on the use of lipophilic anions as the extractants. These anions, typically the conjugate bases of carboxylic acids, beta-diketones, phosphoric/phosphonic/phosphinic acids, phenols, hydroxyoximes, and sulfonic acids, complex to the cation in question with a selectivity set largely by the local anion-cation coordination environment. However, in this communication the ORNL team has shown that when a calix[4]pyrrole is added to a phenolate-type cation extractant the inherent selectivity is pushed in favor of Cs+ over Na+. This bias in favor of Cs+, which stands in contrast to what would normally be expected, is rationalized in terms of the formation of a highly specific tertiary supramolecular complex involving the calix[4]pyrrole, the anionic phenolate, and the Cs+ cation. Such an organized ternary complex is disfavored in the case of Na+. This work is particularly appealing to me as an Associate Editor for its combination of novelty, insightfulness, and scholarly rigor. It is also attractive to me personally because it demonstrates a new utility for one of my favorite old-but-new molecules, namely calix[4]pyrrole.”

Bonus article: “p-Phosphonic acid calix[8]arene mediated synthesis of ultra-large, ultra-thin, single-crystal gold nanoplatelets” by  et al., as chosen by Jonathan Steed:

“This work reports a very simple system that gives glorious gold nanoplatelets with significant surface area but a thickness of around 6nm. Creating 2D nanocrystals is very challenging and involves highly kinetic conditions. In this case the simple reduction of soluble gold(III) in the presence of a phosphonated acid calix[8]arene macrocycle gives rise to these very well-defined and very unusual morphologies. In this case the role of the calixarene seems to be to attach to the Au(111) surfaces, impeding their growth in one direction and allowing growth in the other to form single-crystal platelets. We are still just scratching the surface of what unusual nanoscale morphologies can do to alter the properties of a material but the present gold nanowafers already show promise as oxygen sensors.”

Find our full Editor’s Choice collection online!

Keep up-to-date with our latest journal news on Twitter @ChemCommun!

Learn more about ChemComm online! Submit your latest high impact research here!

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Raffaella Buonsanti and Corinna Schindler: Winners of the ChemComm Emerging Investigator Lectureship 2019!

Raffaella Buonsanti

Raffaella Buonsanti obtained her PhD in Nanochemistry in 2010 at the National Nanotechnology Laboratory, University of Salento. Afterwards, she moved to the US where she spent over five years at the Lawrence Berkeley National Laboratory, first as a postdoc and project scientist at the Molecular Foundry and after as a tenure-track staff scientist in the Joint Center for Artificial Photosynthesis.

She is currently a tenure-track Assistant Professor in the Institute of Chemical Sciences and Engineering at EPFL in Switzerland. Her group works at the interface of materials chemistry and catalysis, using colloidal chemistry tools to synthesize controlled and tunable nanocrystals and to advance the current knowledge on the electrocatalytic conversion of small molecules into value-added chemicals. You can also learn more about Raffaella’s group and research on Twitter @lnce_epfl.

 

 

 

Corinna Schindler

Corinna was awarded her PhD in 2010 at the ETH Zurich, where she worked with Professor Erick M. Carreira on the total synthesis of Banyaside B and Microcin SF608. She has been awarded several honors during her independent career, including a 2016 David and Lucile Packard Foundation Fellowship, a 2016 NSF CAREER award, a 2018 Alfred P. Sloan Research Fellowship, a 2018 Camille Dreyfus Teacher-Scholar Award, a 2019 Marion Milligan Mason Award, and a 2019 Presidential Early Career Award for Scientists and Engineers.

She is currently an Assistant Professor at the University of Michigan, Ann Arbor and her group’s research focuses on the development of new synthetic transformations relying on environmentally benign metals and the synthesis of complex molecules of biological importance in cancer treatment and infectious diseases. Find more info about Corinna and her group on Twitter @SchindlerLab.

 

 

 

 

As part of the Lectureship award, Raffaella and Corinna will each present lectures at three locations over the coming year, with at least one of these events taking place at an international conference. Details of the lectures will be announced in due course but keep an eye on Twitter @ChemCommun for details!

Keep up-to-date with our latest journal news on Twitter @ChemCommun or via our blog!

Learn more about ChemComm online! Submit your latest high impact research here!

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