Paper of the month: Visible light enabled para-fluoro-thiol ligation

Engelke and Truong demonstrate a light-induced para-fluoro-thiol reaction using the photogeneration of a superbase.

 

Graphical abstract for the paper

Post polymerisation modification of macromolecules enables the rapid synthesis of a wide range of polymers with different properties from the same starting material. One promising post polymerisation modification strategy is para-fluoro-thiol reaction (PFTR) which can be further expanded through the use of light as an external stimulus. In this work, Engelke and Truong describe a facile method towards light-enabled PFTR by employing the thioxanthone- 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) salt for light-induced activation of PFTR. The authors exploit this strategy in polymer chemistry by grafting various thiol-containing molecules to a post polymerisation modified backbone and by inducing polymer crosslinking.

The very fast release of DBU under visible light irradiation (blue light, 420 nm) allows for efficient para-fluorothiol ligation which can be used in the synthesis of small thioether molecules. Importantly, this photochemical process could be realized in very high yields (typically >85%) and the product can be easily isolated from the salt by products. The unique aspect of this approach is the temporal control over the photo-induced ligation compared to all other reactions employing photogeneration of a base catalyst, where the reaction continues even when the light is turned off. The PFT ligand could also be initiated by sunlight thus offering for a non-invasive and low-cost technique for the fabrication and modification of complex macromolecular structures. The authors are confident that such strategy mediated by external stimuli will be highly advantageous for soft lithography applications generating micro-and nanosized architectures.

 

 

Tips/comments directly from the authors:

 

1)  Don’t be turned off by the synthesis of the caged DBU.  It’s very straightforward and most of the steps are high yielding. In the step where poly(phosphoric acid) is used, a mechanical stirrer is highly recommended as the mixture can become quite viscous.

2)  The exciting aspect of this work is the efficient uncaging by sunlight which, as an energy source, is non-destructive, low-cost and pollution-free.

3)  Since DBU is a popular organocatalyst for some very important polymerization techniques, such as the ring opening polymerization of lactides and cyclic carbonates, or the polycondensation of isocyanate and polyols. This strategy could be employed for light-mediated polymerization of such monomers, enabling the synthesis of materials that would not be possible to access otherwise.

4)  It was quite fun to see the CO2 bubble (through a cannula) as soon as the light was switched on!

 

Citation to the paper: Visible light enabled para-fluoro-thiol ligation, Polym. Chem., 2020, 11, 7015-7019, DOI: 10.1039/D0PY01373K

Link to the paper: https://pubs.rsc.org/en/content/articlepdf/2020/py/d0py01373k

 

Athina Anastasaki

Dr. Athina Anastasaki is an Editorial Board Member and a Web Writer for Polymer Chemistry. Since January 2019, she joined the Materials Department of ETH Zurich as an Assistant Professor to establish her independent research group.

 

 

 

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Polymer Chemistry Author of the Month: Hans R. Kricheldorf

Hans R. Kricheldorf studied chemistry at the University of Freiburg im Breisgau where he obtained his master degree in 1967 and his PhD in 1969. He continued his academic career as assistant Professor at the “Institut für Makromolekulare Chemie” in Freiburg im Breisgau and achieved the tenure (Habilitation) in 1975 (awarded a prize by the Association of the German Chemical Industry). He was appointed Associate Professor at the same institute in 1980 and Full Professor of polymer chemistry at the University of Hamburg in 1982. He retired in 2008, but continued to perform experimental research without coworkers. His life-long working fields were ring-opening polymerization and polycondensation. During the past twenty years his interest was focused on syntheses of biodegradable polymers, interactions between ROP and polycondensation, and syntheses of cyclic and multicyclic polymers. He is author or coauthor of more than 800 peer-reviewed papers and patents and author, coauthor and/or editor of a dozen of books. Recently he was awarded the “Korshak Prize” of the Russian Academy of Sciences for his life-work on polycondensation.

What was your inspiration in becoming a polymer chemist?

My inspiration in becoming a polymer chemist had two sources. In the age of 15 I became interested in chemical experiments primarily in syntheses of explosives. In the age of 18 this hobby ended with a stay in a hospital, but at that time I was proud to have a collection of 27 different explosives. As a student I was mainly in organic chemistry, but when I had to select a research group for my PhD work, I decided for two reasons to enter the field of polymer chemistry. Firstly, I had the vision that there will be more space for fundamental research, because this part of chemistry was relatively new compared to organic and inorganic chemistry.  Secondly, the university of Freiburg im Breisgau with the Institut für Makromolekulare Chemie was a particularly attractive place to start a career in polymer chemistry, because the first Nobel Prize laureate in polymer science, Prof. H. Staudinger, had worked here for more than 30 years. When I was a young student I saw him twice one year before his death and he impressed me. I joined the group of Assoc. Prof. G. Greber (later Full Prof. and director at the Tech. Univ. of Vienna) who was the last PhD student of H. Staudinger. By joining his group, I became so-to-say a scientific grandson of H. Staudinger.

What was the motivation behind your most recent Polymer Chemistry article ?

My motivation behind my recent work was an attempt to close two gaps in my knowledge about ring-opening polymerization of lactide (and lactones). For the technical production of poly(l-lactide) (meanwhile approaching 700 000 t/pa) tin(II) 2-ethlyhexanoate is the most widely used catalyst. For the technical production an alcohol is used as initiator to control the molecular weight and to accelerate the polymerization. However, over the past 20 years nobody has elucidated what happens in the absence of an initiator. Furthermore, I have recently defined and described a new type of polymerization called ROPPOC (ring-opening polymerization combined with simultaneous polycondensation). Introduction of a highly electrophilic and group via the catalyst is the key to success. However, catalysts introducing an anhydride group were still lacking in my collection of ROPPOC catalysts. The results obtained with Sn(II) acetate or 2-ethylhexanoate have now closed these gaps.

Which polymer scientist are you most inspired by?
My research activities of the past twenty years were mainly inspired by the work of Wallace H. Carothers, Paul J. Flory (Nobel Prize 1974) and Walter H. Stockmayer. These scientists formulated the experimental and theoretical fundament of step-growth polymerizations. However, when reading their papers, I had the impression that part of their theories, primarily their understanding of cyclization reactions, was incorrect. Therefore, I have spent much time and work with elaborating sufficient evidence for the correctness of my view. By the way, I became acquainted with both Flory and Stockmayer before 1985 and I was impressed by their personalities. But at that time, I had not worked yet on the aforementioned problems, so that our discussions touched other working fields.

How do you spend your spare time?

Forty years ago, I have begun to learn horse riding and over the past thirty years I had two horses. But recently I had to euthanize my second horse because of an accident, and now I’m to old to begin with a new horse. However, I continue to perform gym including bicycling and swimming to maintain my fitness as good as I can. Another major hobby is history, because any object and any idea has a history, and knowing more about the past means better understanding of the present. In this connection I have written several books after my retirement, for example a book about the most important 15 materials that form the fundament of our civilization, a book about history and philosophy of the natural sciences, a book about the history of polycondensation and most recently a book discussing the question, if life is the consequence of a chemical evolution.

What profession would you choose if you weren’t a scientist?

I had chosen to become physician, probably specialized in radiology. In the aftermath I indeed regret that I have decided to study chemistry. In the years 1995-2010 I had a cooperation with Prof. Ch. Jürgens (surgeon and director at a big hospital in Hamburg) on applications of biodegradable films for dressing of large burn wounds and as tissue-separating films. Our films (mainly consisting of lactide) were commercialized under the trade marks “Topkin” and “Mesofol “, but the Merck-Biomet company which produced  these films stopped the production after ten years for financial reasons, and thus, our films did not become a big success. Nonetheless, our films supported an almost painless healing of more than 500 patients. From this cooperation I have learned that it is more satisfactory for me to help patients to recover from their wounds than publishing several more papers on polymer chemistry.

 

Read Hans’ full article now

 


 

High molar mass cyclic poly(l-lactide) obtained by means of neat tin(ii) 2-ethylhexanoate

Hans R. Kricheldorf  and  Steffen M. Weidner

L-Lactide was polymerized in bulk at 120, 140, 160 and 180 °C with neat tin(II) 2-ethylhexanoate (SnOct2) as the catalyst. At 180 °C the Lac/Cat ratio was varied from 25/1 up to 8000/1 and at 160 °C from 25/1 up to 6000/1. The vast majority of the resulting polylactides consist of cycles in combination with a small fraction of linear chains having one octanoate and one COOH end group. The linear chains almost vanished at high Lac/Cat ratios, as evidenced by MALDI-TOF mass spectrometry and measurements of intrinsic viscosities and dn/dc values. At Lac/Cat ratios <1000/1 the number average molar masses (Mn) are far higher than expected for stoichiometic initiation, and above 400/1 the molar masses vary relatively little with the Lac/Cat ratio. At 180 °C slight discoloration even at short times and degradation of the molar masses were observed, but at 160 °C or below colorless products with weight average molar masses (Mw) up to 310 000 g mol−1 were obtained. The formation of high molar mass cyclic polylactides is explained by a ROPPOC (Ring-Opening Polymerizatiom with simultaneous Polycondensation) mechanism with intermediate formation of linear chains having one Sn–O–CH end group and one mixed anhydride end group. Additional experiments with tin(II)acetate as the catalyst confirm this interpretation. These findings together with the detection of several transesterification mechanisms confirm the previous critique of the Jacobson–Stockmayer theory.

 


About the Webwriter

Simon HarrissonSimon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based at the Laboratoire de la Chimie des Polymères Organiques (LCPO) in Bordeaux, France. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

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Paper of the month: Thermoresponsive properties of poly(acrylamide-co-acrylonitrile)-based diblock copolymers synthesized (by PISA) in water

Audureau et al. report the synthesis of UCST-thermoresponsive diblock copolymers using reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous media.

Image describing the paper

Thermoresponsive polymers have attracted widespread interest in both fundamental research and industrial applications due to their special ability to change properties upon cooling or heating. Polymers exhibiting upper critical solution temperature (UCST) are soluble in a solvent above the UCST but precipitate from the same solvent when cooling below its critical temperature. In the large UCST polymer family, the statistical copolymer poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) has gained increasing interest and has been used to prepare nanoparticles for drug delivery, cancer theranostics/chemotherapy and photoacoustic imaging. However, a method for scalable synthesis of thermoresponsive P(AAm-co-AN) block copolymer in water and in-situ self-assembly of the resulting copolymers into nanoparticles remains elusive. In this work, Rieger, Stoffelbach and co-workers employed polymerization-induced self-assembly technique (PISA) to synthesize, for the first time in water, well-defined P(AAm-co-AN) block copolymers which self-assembled into nanoparticles. Importantly, the rare worm-like morphology was successfully obtained, which paves the way for developing better cancer drug delivery systems since nanoworms have distinct and advantageous properties when compared to their spherical counterparts such as long circulation time, high accumulation in tumour and deep tumour penetration. Furthermore, an interesting worm-to-sphere morphological transition was observed upon heating the nanoworms solution. This is in contrast to previous reports where a worm-to-sphere transition was only demonstrated upon cooling and therefore, offers a new promising strategy to design novel smart nanoparticles for various applications.

 

Tips/comments directly from the authors:

 

1)  The thermoresponsive properties of the copolymers crucially depend on the molar fraction of acrylonitrile (FAN) in the P(AAm-co-AN) block, tunable by the initial AN fraction (fAN) in the monomer feed. As AN is volatile, a closed Schlenk system should be used to avoid monomer evaporation during polymerization and produce polymers with predictable properties.

2) P(AAm-co-AN) statistical copolymers exhibited a typical UCST-type thermal transition for acrylonitrile molar fractions (FAN) ranging from 0.3 to 0.5.

3) In addition to FAN, the presence of a hydrophilic PDMAc block and the DPn of the polymer blocks also impact the thermoresponsiveness.

 

Citation to the paper: Thermoresponsive properties of poly(acrylamide-co-acrylonitrile)-based diblock copolymers synthesized (by PISA) in water), Polym. Chem., 2020, 11, 5998-6008, DOI: 10.1039/D0PY00895H. Link to the paper here.

More papers on PISA can be found at our themed collection here!

 

About the web writer:

Professor Athina Anastasaki

Dr. Athina Anastasaki is an Editorial Board Member and a Web Writer for Polymer Chemistry. Since January 2019, she has joined the Materials Department of ETH Zurich as an Assistant Professor to establish her independent research group.

 

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Open for Nominations: 2021 Polymer Chemistry Lectureship

Do you know an early-career researcher who deserves recognition for their contribution to the polymer chemistry field?

Now is your chance to put them forward for the accolade they deserve!

Polymer Chemistry is pleased to announce that nominations are now being accepted for its 2021 Lectureship award. This annual award was established in 2015 to honour an early-stage career scientist who has made a significant contribution to the polymer field.

The recipient of the award will be asked to present a lecture at an international conference in 2021, where they will also be presented with the award. The Polymer Chemistry Editorial Office will provide £1000 financial support to the recipient for travel and accommodation costs.

The recipient will also be asked to contribute a research article to the journal and will have their work showcased free of charge on the front cover of the issue in which their article is published. The article would be subject to the normal peer review standards of the journal.

 

Previous winners

2020 – Rachel O’Reilly, University of Birmingham, UK

2019 – Frederik Wurm, University of Twente, The Netherlands

2018 – Cyrille Boyer, University of New South Wales, Australia

2017 – Julien NicolasUniversité Paris Sud, France

2016 – Feihe Huang, Zhejiang University, China

2015 – Richard Hoogenboom, Ghent University, Belgium

 

Eligibility

To be eligible for the lectureship, candidates should meet the following criteria:

  • Be an independent researcher, having completed PhD and postdoctoral studies
  • Be actively pursuing research within the polymer chemistry field, and have made a significant contribution to the field
  • Be at an early stage of their independent career (this should typically be within 12 years of attaining their doctorate or equivalent degree, but appropriate consideration will be given to those who work in systems where their time period to independence may vary, or who have taken a career break, for example for childcare leave or who followed an alternative study path)

Although the Polymer Chemistry Lectureship doesn’t explicitly reward support of or contributions to the journal, candidates with a history of publishing or reviewing for the journal would be more likely to be considered favourably.

 

Selection

  • All eligible nominated candidates will be assessed by a shortlisting panel, made up of members of the Polymer Chemistry Advisory Board and a previous lectureship winner.
  • The shortlisting panel will consider the nomination form and letter of recommendation, as well as the three recent research articles highlighted in the nomination form for consideration.
  • Shortlisted candidates will be further assessed by the Polymer Chemistry Editorial Board, and a winner will be selected based on an anonymous poll.
  • Selection is not based simply on quantitative measures. Consideration will be given to all information provided in the letter of recommendation and nomination form, including research achievements and originality, contributions to the polymer community, innovation, collaborations and teamwork, publication history, and engagement with Polymer Chemistry.

 

Nominations

Nominations must be made via email to polymers-rsc@rsc.org, and include the following:

  • A brief letter of recommendation (1 page maximum length)
  • A complete nomination form (includes list of the candidate’s relevant publications or recent work, 3 research articles to be considered during the shortlisting process, candidate’s scientific CV, and full contact details)

Please note:

  • Nominations from students and self-nomination is not permitted.
  • The nominee must be aware that he/she has been nominated for this lectureship.
  • As part of the Royal Society of Chemistry, we have a responsibility to promote inclusivity and accessibility in order to improve diversity. Where possible, we encourage each nominator to consider nominating candidates of all genders, races, and backgrounds. Please see the RSC’s approach to Inclusion and Diversity.
  • Candidates outside of the stated eligibility criteria may still be considered.

 

Nominations deadline: 31st December 2020

 

Download nomination form here

 

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Polymer Chemistry Author of the Month: Jiangtao (Jason) Xu

Dr. Jason Xu is an Australian Research Council (ARC) Future Fellow at School of Chemical Engineering, UNSW Sydney. He is currently leading a research group in the Cluster for Advanced Macromolecular Design (CAMD) and Australian Centre for NanoMedicine (ACN), with the focus on green and precision polymer synthesis using state-of-the-art polymerization techniques and organic chemistry tools. Dr. Xu received his BS and PhD Degrees (2007) in Polymer Chemistry from Fudan University. Following post-doctoral research in UNSW and University of Melbourne and industrial experience, he joined UNSW to develop visible light-induced living polymerization and precision polymer synthesis. He has more than 100 peer-reviewed publications in high-impact journals, attracting over 6300 citations and an h-index of 45. His areas of research interests are green chemistry and sustainable polymer synthesis, precision polymer synthesis mimicking natural perfection, advanced polymer hydrogels for strain and bio-sensors.

What was your inspiration in becoming a polymer chemist?

When I was still a freshman in the university, polymer chemistry was still a young and rising area at the end of 20th century in China, full of mysteries and possibilities. I was inspired by a lecture delivered by a professor in our school who is one of the pioneering researchers in polymer chemistry. He presented the amazing properties of liquid crystal polymers and foreseeable future of these materials. After that, I started to learn more about polymers and I knew polymers have already been everywhere in our life, plastics and rubbers and synthetic resins. However, there are still many things unknown for polymers, particularly for polymer chemistry. How to design and synthesize these gigantic molecules with the properties we want? This is the question, from then on, always in my mind.

What was the motivation behind your most recent Polymer Chemistry article in the Pioneering Investigators collection?
Natural biopolymers (DNA and peptides) have uniform microstructures with defined molecular weight and precise monomer sequence along the polymer chain that affords them unique biological functions. To reproduce such structurally perfect polymers through chemical approaches, researchers have proposed using synthetic polymers as an alternative. Different methodologies have been developed in the last decades. We recently proposed an emerging technology of single unit monomer insertion (SUMI), which is very similar to peptide synthesis from amino acids. SUMI can precisely prepare uniform and monodisperse alternating polymers using sequential addition of two monomers. However, the characterization of precision structure is getting harder and harder while the polymer chain increases. We therefore propose a series of short oligomers with three monomer units (trimers) to model the reaction for each step. These model trimers can provide the detailed reaction kinetics and mechanism as well as product yields, which will be the same as the reactions in long chain polymer synthesis due to the repeating monomer additions. These model trimers can also provide the reaction kinetics for copolymerization of corresponding monomers.

Which polymer scientist are you most inspired by?
There are many excellent polymer scientists I was most inspired by, such as Professors Craig Hawker and Masami Kamigaito in my mind as examples. Craig is full of very useful and bright ideas covering broad polymer area in chemistry and materials. Our recent photopolymerization technology of PET-RAFT is inspired by his pioneering work in 2012. Masami is at the forefront of polymer synthesis. His work in green polymer synthesis using renewable monomers from natural plants is fascinating.

Can you name some up and coming researchers who you think will have a big impact on the field of polymer chemistry?

This is an interesting but difficult-to-answer question. From my point of view in the specific field of polymer synthesis, there are many young and smart researchers whose research is believed to have a big impact, such as Professors Brett Fors (Cornell) and Athina Anastasaki (ETH) as examples. Their recent excellent works in photocontrolled cationic polymerization and precise polymer dispersity control are good evidence to demonstrate their potential to impact the field. Their contribution will push forward the field of polymer synthesis.

How do you spend your spare time?
I spend my spare time with my family to go out for BBQ and hiking. My daughter is currently two years old, which requires a lot of accompanying and brings so much fun to my life. Also, I like very much playing badminton and have been playing for more than 15 years. It is one of my favorite sports because it is free of any body contact different from basketball or soccer, but still requires the strength, balance and motion skills. It is therefore one of the sports anyone can keep for their whole life.

What profession would you choose if you weren’t a scientist?

I would choose my profession to be an automotive mechanic. Auto mechanic is a “precision” job like a doctor. It requires to know how all different auto parts been designed and how they work synergistically, which enables to quickly diagnose and fix the mechanical malfunction. As a mechanic, the body and mind will work all the time, which can keep the mind sharp and the body active and healthy. Actually, I hold a TAFE Auto mechanic certificate and always had a plan to run a workshop. What I need now is the financial support from some potential investors (kidding!).

Read Jason’s full article now for FREE until 17 November!

Also check our the work of our other Pioneering Investigators here

 


Sequential and alternating RAFT single unit monomer insertion: model trimers as the guide for discrete oligomer synthesis

Graphical abstract: Sequential and alternating RAFT single unit monomer insertion: model trimers as the guide for discrete oligomer synthesis

Sequence-defined polymers have garnered increasing attention in a broad range of applications from materials engineering to medical science. Reversible addition–fragmentation chain transfer single unit monomer insertion (RAFT SUMI) technology has recently emerged as a powerful tool for sequence-defined polymer synthesis, which utilizes sequential monomer radical additions occurring one unit at a time to assemble olefins into uniform polymers. The strategy of employing alternating additions of electron-donor and acceptor (D–A) monomers can be used to prepare long chain sequence-defined polymers by the RAFT SUMI technique. However, considering both terminal and penultimate unit effects, complex radical reaction kinetics can result from various monomer addition orders particularly if three or more different families of vinyl monomers are used to build diverse sequences. Simplifying reaction processes and establishing reaction kinetics will be critical for effective synthesis of sequence-defined polymers. Herein, a series of model trimers containing D–A–D and A–D–A triads was thus produced from four families of α,β-disubstituted vinyl monomers (N-phenylmaleimide, fumaronitrile and dimethyl fumarate and indene). Such trimers presented distinct synthesis kinetics (reaction rate and yield). These model trimers and their kinetics data are able to provide full guidance for the synthesis of long chain discrete polymers using sequential and alternating RAFT SUMI processes.


About the Webwriter

Simon HarrissonSimon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based at the Laboratoire de la Chimie des Polymères Organiques (LCPO) in Bordeaux, France. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

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Paper of the month: Direct laser writing of poly(phenylene vinylene) on poly(barrelene)

Bielawski and co-workers report the ROMP of barrelene monomer affording precisely defined fluorescent patterns with micrometer-sized dimensions.

 

 

Conjugated polymers have attracted considerable attention owing to their abilities to form films and exhibit high electrical conductivities and as such they have found use in a range of electronic and optical applications. Amongst the various types of polymers, poly(phenylene vinylene) (PPV) is an excellent candidate due to its low optical band gap, large nonlinear optical response, and emissive properties. However, this material is typically intractable and thus challenging to process. To overcome this, Bielawski and co-workers designed a new approach to PPV was through the ring-opening metathesis polymerization (ROMP) of “barrelene” (bicyclo[2.2.2]octa-2,5,7-triene). The monomer was characterized for the first time by X-ray diffraction analysis of a coordination complex. Barrelene was subsequently homopolymerized and copolymerized with norbornene. The solubility of barrelene homopolymers was found to depend on the cis to trans ratio of alkene in its backbone. Both the homo and copolymers were transformed to PPV by undergoing spontaneous dehydrogenation under air. The materials were analyzed by a range of spectroscopic techniques. Importantly, direct laser writing of the barrelene-containing copolymers was also demonstrated resulting in thermal aromatization within a few seconds affording precisely defined fluorescent patterns with micrometer-sized dimensions. An intrinsic advantage of this development is that the monomer can be potentially incorporated into different macromolecular scaffolds and at varying compositions. Owing to this unique characteristic, the authors envision that their designed strategy would enable the synthesis of a broad range of materials for use in laser machining and contemporary lithography applications.

 

Tips/comments directly from the authors:

 

1)  The solubility of poly(barrelene) is dependent on the cis-to-trans ratio of the exocyclic olefins in the polymer backbone. Polymers with relatively high cis olefin contents appear to be more soluble than their trans isomers.

2)  The resolution of the patterns created by direct laser writing appear to be inversely proportional to the barrelene content of the copolymer used and may be enhanced further by increasing the transparency of the films.

3)  Poly(barrelene) oxidizes in air (slow) or upon laser irradiation (fast). A convenient way to monitor the oxidation reaction is through fluorescence spectroscopy. The starting material is non-emissive whereas the poly(phenylene vinylene) product emits a fluorescent green color upon excitation.

4)  Because barrelene is strained, copolymerization with other monomers used in ring-opening metathesis polymerization methodologies can be expected which, in turn, may expand the utility of the direct laser writing technique.

 

Citation to the paper: Direct laser writing of poly(phenylene vinylene) on poly(barrelene), Polym. Chem., 2020, 11, 5437-5443, DOI: 10.1039/d0py00869a

 

Link to the paper:

https://pubs.rsc.org/en/content/articlepdf/2020/py/d0py00869a

Professor Athina AnastasakiDr. Athina Anastasaki is an Editorial Board Member and a Web Writer for Polymer Chemistry. Since January 2019, she joined the Materials Department of ETH Zurich as an Assistant Professor to establish her independent research group.

 

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Paper of the month: Single-chain crosslinked polymers via the transesterification of folded polymers: from efficient synthesis to crystallinity control

Terashima and co-workers report efficient synthetic systems of single-chain crosslinked polymers.

 

Crosslinked polymers have emerged as a class of unique materials which find use in a diverse range of applications such as drug delivery, dispersants and coating industries. Typically, those materials are made through a combination of controlled polymerization and crosslinked methods. In this work, Terashima and co-workers prepared a range of single-chain crosslinked polymers with controlled crystallization. This was achieved by the intramolecular transesterification of random copolymers compromising of octadecyl methacrylate, 2-hydroxyethyl methacrylate, and methyl acrylate. Those copolymers were self-folded in organic media (octane was used as the solvent) through the association of the hydroxyl groups to form reverse micelles. Upon synthesis, the micelles were intramolecularly crosslinked by an efficient transesterification of the methyl acrylate units with the hydroxyl groups to produce polymer nanoparticles with pending octadecyl groups. The materials synthesized were thoroughly characterized by a number of techniques including nuclear magnetic resonance, gel permeation chromatography, small angle X-ray scattering and dynamic light scattering. The developed system allowed for the efficient control of the molecular weight of the crosslinked polymers owing to the precise synthesis of the precursors prepared by living radical polymerization. Importantly, the degree of crosslinking was found to control the crystallinity of the products. Last but not least, a relatively high concentration could be used (up to 50 mg ml-1).  As the authors allude to in their conclusion, their work has paved the way to the production of well-defined polymeric nanoparticles that can be employed for surface coating, painting, optical plastics and cosmetics.

 

Tips/comments directly from the authors:

 

1) Intramolecular crosslinking of folded polymers in organic media via transesterification affords the precision and high-throughput synthesis of single-chain crosslinked polymer nanoparticles.

2) The molecular weight of the crosslinked polymers can be controlled as desired at the stage of the synthesis of the precursor polymers by controlled radical polymerization.

3) Transesterification between hydroxyl groups and methyl acrylate units efficiently proceeds within the cores of folded micelles to fix the folded structures in a specific solvent.

4) SEC-MALLS analysis is essential to characterize single-chain crosslinked polymers. Because of the compact structures, the apparent molecular weight of the crosslinked polymers by the general RI detector with PMMA standard calibration turns smaller than that of the non-crosslinked precursor polymers. If the absolute weight-average molecular weight of the crosslinked polymers by the MALLS detector is also close to that of the precursor polymers, you can conclude that the products consist of single chain-crosslinked polymers.

5) Crystallinity of the bulk polymers is controlled by tuning the degree of intramolecular crosslinking. This is an interesting approach to control the thermal and physical properties of solid polymer materials.

Citation to the paper: Single-chain crosslinked polymers via the transesterification of folded polymers: from efficient synthesis to crystallinity control, Polym. Chem., 2020, 11, 5181-5190, doi.org/10.1039/D0PY00758G

Link to the paper: https://pubs.rsc.org/en/content/articlepdf/2020/py/d0py00758g

About the web writer:

Professor Athina Anastasaki

Dr. Athina Anastasaki is an Editorial Board Member and a Web Writer for Polymer Chemistry. Since January 2019, she joined the Materials Department of ETH Zurich as an Assistant Professor to establish her independent research group.

 

 

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Polymer Chemistry Author of the Month: Urara Hasegawa

Urara Hasegawa received her B.S. and M.Eng. in Applied Chemistry from Waseda University (Japan). She earned her Ph.D. in Biomedical Science from Tokyo Medical and Dental University (Japan) under the supervision of Professor Kazunari Akiyoshi. Then, she worked as a postdoctoral fellow in the lab of Professor Jeffrey Hubbell at École Polytechnique Fédérale de Lausanne (EPFL) (Switzerland). She joined the Department of Applied Chemistry at Osaka University (Japan) as an assistant professor in 2011, and then moved to the Department of Chemical Engineering at Kansas State University in 2017. In 2020, she joined the Department of Materials Science and Engineering at Pennsylvania State University. Her research focuses on development of polymeric nanomaterials for controlled delivery of drugs and bioactive signaling molecules. She has published more than 45 peer-review papers and has received several awards including a NSF CAREER award in 2020.

 

What was your inspiration in becoming a polymer chemist?

When I was an undergraduate student, I had the opportunity to learn about cell sheet engineering developed by Professor Teruo Okano at Tokyo Women’s Medical University. They used surfaces coated with poly(N-isopropyl acrylamide) (PNIPAM) as a temperature-responsive tissue culture plate, which enables to harvest cultured cells by lowering temperature below the lower critical solution temperature of PNIPAM. This technology solved the problems associated with conventional techniques requiring a proteolytic enzyme to detach cells. I was excited to see how synthetic polymers can be used to manipulate living cells. Since then, I have developed a strong interest in polymer chemistry that can contribute to the advance of biomedical technologies.

What was the motivation behind your most recent Polymer Chemistry article?

I’m particularly interested in gaseous signaling molecules (gasotransmitters) such as nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S), which are generated ubiquitously in our body and serve as essential signaling regulators in many physiological and pathological processes. One of the challenges in gasotransmitter research is the lack of delivery technologies, which enable the delivery of a known amount of gasotransmitter for a specific period of time to target cells and tissues. So far, significant efforts have been made to develop small gas donor compounds that decompose to generate gasotransmitters under physiological conditions. However, the use of these compounds is limited due to the fast and uncontrolled gas release rate and toxic side effects of the donor compounds and/or their decomposition byproducts.

In the past years, my research group has been focused on developing polymeric micelles for delivery of NO, CO and H2S to cells. We have been successful in showing the advantages of using polymeric micelles for gasotransmitter delivery by slowing down release rate, reducing toxic side effects and improving therapeutic efficacy. In the recent Polymer Chemistry article, we demonstrated that H2S release rate from polymeric micelles can be modulated by controlling micellar stability, which significantly affects proangiogenic activity of these H2S-releasing micelles. The developed technology will be used as a delivery tool to enhance the fundamental understanding of H2S biology, which will lead to development of innovative approaches for the prevention and treatment of a variety of diseases.

Which polymer scientist are you most inspired by?

Although there are so many remarkable researchers in the field of polymeric biomaterials science, Professor Helmut Ringsdorf at University of Mainz and Professor Jindřich Kopeček at University of Utah are the researchers who I’m inspired by. They developed the concept of “polymer-drug conjugate” in the mid 1970’s to improve solubility and blood circulation time of drugs as well as confer targeting capability. Another researcher who influenced my work is Professor Kazunori Kataoka at University of Tokyo. He is the pioneer of polymeric micelles for drug delivery.

How do you spend your spare time?
I enjoy spending time with my cats. I like to see them sleeping in the most cozy and comfortable spots in the house and hear them purring when I’m patting them. I also love visiting different places and enjoy local foods and cultures. I recently found a new hobby: Origami (Japanese style paper folding). This is a good way to relax and refresh my mind.

What profession would you choose if you weren’t a scientist?

I still would like to choose a job related to science. A graphic designer for scientific illustration could be a profession I would be interested in. I feel graphics are a powerful tool to explain the essence and concepts of research and increase impact of new technologies and scientific findings. I love to draw and would enjoy contributing to science even if I were not a scientist.

Read Urara’s full article now for FREE until 8 October

 


Hydrogen sulfide-releasing micelles for promoting angiogenesis


About the Webwriter

Simon HarrissonSimon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based at the Laboratoire de la Chimie des Polymères Organiques (LCPO) in Bordeaux, France. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

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Paper of the month: Sequential and alternating RAFT single unit monomer insertion: model trimers as the guide for discrete oligomer synthesis

Xu and co-workers utilize model trimers as a guide for discrete oligomer synthesis.

 

Image describing the synthesis of sequence-defined polymers from model trimers

Biomacromolecules such as DNA and proteins exhibit perfect sequence precision which allows them to fulfill a number of biological functions. A long-lasting challenge in polymer chemistry is to mimic these biopolymers through synthetic analogues. In particular, single unit monomer insertion technique has emerged as a powerful tool to synthesize sequence-defined polymers with perfect uniformity. Key to this approach is the alternating addition of electron-donor and acceptor monomers which can be utilized to prepare long polymer chains through sequential monomer radical additions occurring one unit at a time. Despite notable progress in the last decades, such alternative and sequential monomer additions often produce complex radical reaction kinetics which makes the formation of diverse polymer sequences challenging. To this end, simplifying reaction processes and establishing simple reaction kinetics is essential to bring a rapid and reliable synthesis. In this work, Xu and co-workers describe a methodology to address this challenge by employing model trimers as a guide for the synthesis of sequence-defined polymers. Central to the design is the sequential and alternating PET-RAFT SUMI technology which enables the acquisition of full kinetic data, thus providing a very useful insight over both reaction rates and yields. Four different families of α,β-disubstituted vinyl monomers (N-phenylmaleimide (PMI), fumaronitrile (FCN) and dimethyl fumarate (DMF) and indene (Ind)) were employed to prepare nine model trimers. These model compounds were subsequently utilized to guide the synthesis of longer discrete polymers (pentamers with diverse monomer sequences) through multiple insertions yielding materials with high isolated yields. The authors’ findings were supported by nuclear magnetic resonance and mass-spectrometry which were used to establish reaction rate and product purity respectively. The authors anticipate that their method can also be applied to other vinyl polymers and different RAFT initiation systems. Such monodispersed materials with perfect sequence control are expected to find use in a range of applications.

 

Tips/comments directly from the authors:

1)  The use of automated flash chromatography can effectively simplify the SUMI product purification and allows for a more efficient and reproducible synthesis.

2) The online-NMR spectroscopy is an effective technique to monitor RAFT agent and monomer conversion in RAFT SUMI.

3)  There are several diastereoisomers for each of SUMI products that would show different polarities in column chromatography and complicated NMR spectra. Careful implementation and thoughtful data analysis are required.

4) The characterization of long chain oligomers (more than four monomer units) is quite challenging. Only mass spectrometry is available for the structure confirmation. Therefore, the model trimers are very important to guide the synthesis of long chain oligomers. All triad sequences in long chain oligomers can be found in the model trimers.

5). The established model trimers and kinetics data could also provide experimental and theoretical guidance for the synthesis of alternating polymers and investigation of mechanism and kinetics of radical copolymerization.

 

Citation to the paper: Sequential and alternating RAFT single unit monomer insertion: model trimers as the guide for discrete oligomer synthesis, Polym. Chem., 2020, 11, 4557-4567, DOI: 10.1039/d0py00390e

 

Link to the paper:

https://pubs.rsc.org/en/content/articlepdf/2020/py/d0py00390e

Read more papers from our Pioneering Investigators 2021 collection here!

About the web writer

Dr. AthinProfessor Athina Anastasakia Anastasaki is an Editorial Board Member and a Web Writer for Polymer Chemistry. Since January 2019, she joined the Materials Department of ETH Zurich as an Assistant Professor to establish her independent research group.

 

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Polymer Chemistry Author of the Month: Trang N. T. Phan

Trang N. T. Phan is an Associate Professor in the Institute of Radical Chemistry at Aix-Marseille University in France. She completed her undergraduate studies with a Masters in chemistry and then joined the PhD program in Polymers and Organic Chemistry at University of Lille 1. She received her PhD in 2000 under the supervision of Pr. M. Morcellet. During her PhD at the Macromolecular Chemistry Lab, she worked on the synthesis, characterization and water purification application of sorbents based on silica gel functionalized with β-cyclodextrin based polymers. During 2000-2002, she worked as a postdoctoral researcher at the Materials and Interfaces Chemistry Lab of University of Franche-Comté, first in the European project SILACOR and then in a project with BASF on the adsorption of polyelectrolytes on zinc oxide nanoparticles. In 2002, she joined Pr Denis Bertin’s group, firstly as a temporary lecturer and then as a postdoctoral researcher. In September 2004, she became a full associate professor at Aix-Marseille University in the group of Didier Gigmes. In 2014, she received with her colleagues (R. Bouchet and D. Gigmes) the International Prize EDF PULSE Science and Electricity. Her current research interests are in the design and the synthesis of advanced functional polymers via controlled polymerization techniques for specific applications such as solid polymer electrolytes, polymers blend compatibilizers and structure-directing agents.

 

What was your inspiration in becoming a polymer chemist?

During my Bachelors course work and internship project, I started learning about polymer chemistry. I was fascinated by the “magic” of the transformation of small molecules (monomers) to polymers which are useful functional materials. From that moment, I decided to learn more about how chemistry can help to design and synthesize (co)polymers with precise structure, functionality and composition responding to desired properties and specific applications.

What was the motivation behind your most recent Polymer Chemistry article?

Radical ring-opening polymerization (rROP) of cyclic monomers is an attractive method to synthesize functional polymers bearing both heteroatoms in the backbone and functional groups in the side chain. In addition, the potential applicability of rROPs for copolymerizations with vinyl monomers is a highly attractive feature. Among different cyclic monomers, vinyl cyclopropane (VCP) derivatives were the most promising compounds since their rROPs led to low-shrinkage materials with attractive applications for dental adhesives and composites. However, functional groups in the side chain of VCP polymers are usually limited to halogens, esters and nitrile functions that restrict the development of new functional VCP polymers by post-polymerization modification. During our investigation of new VCP derivatives, we have achieved a straightforward pathway for the synthesis of VCP bearing azlactone functionality. The azlactone group can react via rapid and efficient ring-opening reactions with different nucleophilic species such as primary amines, hydroxyls, and thiols. We expect that the new VCP-azlactone (co)polymers could serve widely as a reactive platform for the introduction of chemical and biological functionality.

Which polymer scientist are you most inspired by?

I am greatly interested by the work being undertaken in the group of Pr. David Mecerreyes since their research allies polymer chemistry, supramolecular chemistry and nanomaterials science to synthesize innovative polymeric materials.

How do you spend your spare time?
I like cooking and experimenting with new recipes by combining western and oriental flavors. After all, cooking is similar to chemistry. I also like hiking and reading.

What profession would you choose if you weren’t a scientist?

I’d be a Scuba dive master practicing somewhere in the warm waters of tropical seas.

Read Trang’s full article now for FREE

 


Radical ring-opening polymerization of novel azlactone-functionalized vinyl cyclopropanes

Azlactone-functionalized polymers are considered powerful materials for bioconjugation and many other applications. However, the limited number of azlactone monomers available and their multistage syntheses pose major challenges for the preparation of new reactive polymers from these monomers. In this article, we report the synthesis of a new class of azlactone monomers based on vinylcyclopropane (VCP). Furthermore, the (co)polymerization of the azlactone-functionalized VCPs has been successfully demonstrated to provide new azlactone polymers by using free-radical polymerization. The ability of the resulting amine-reactive polymers to be engaged in post-polymerization modifications was demonstrated using dansylcadaverine. These new azlactone-functionalized VCP monomers and polymers are potential candidates for the synthesis of innovative (bio)materials.


About the Webwriter

Simon HarrissonSimon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based at the Laboratoire de la Chimie des Polymères Organiques (LCPO) in Bordeaux, France. His research seeks to apply a fundamental understanding of polymerization kinetics and mechanisms to the development of new materials. He is an Advisory Board member for Polymer Chemistry. Follow him on Twitter @polyharrisson

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