Author Archive

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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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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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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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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Polymer Chemistry Author of the Month: Nicholas J. Warren

Nick WarrenNick Warren  is a University Academic Fellow within the School of Chemical and Process Engineering at the University of Leeds. He was awarded an Masters in Chemistry from the University of Bristol in 2005 following which he conducted two years industrial research. He then moved to the University of Sheffield where he studied for a PhD in Polymer Chemistry within Prof Steve Armes’ research group where he focussed on synthesis of biocompatible block copolymers. Following his PhD, he continued as a postdoctoral researcher in Sheffield working in the area of polymerisation-induced self-assembly (PISA) until 2016, when he moved to Leeds to start his independent research career. His current research aims to exploit the latest advances in polymerisation techniques, combined with new reactor technologies for the design and discovery of controlled-structure polymers.

What was your inspiration in becoming a polymer chemist?

During my undergraduate masters project, I worked on development on combining pH responsive microgels with photo-responsive surfactants. I was fascinated by the ability to use chemical composition as a means of tuning physical characteristics of a material and imparting responsive behaviour. This brought on a specific interest in synthetic polymer chemistry, where there are so many synthetic routes to generating responsive materials. This was the focus of my PhD, where I gained expertise in ATRP and RAFT polymerisation which provided a convenient tool-box allowing me to design and synthesise pH responsive block copolymers.

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

Continuous-flow techniques are well utilised in small molecule synthesis and are now becoming commonplace in polymer chemistry. In my research group, we aim to use flow-chemistry to conduct polymer synthesis and try and exploit its characteristics to develop new materials, streamline methods for optimising polymerisation processes; or for detailed online monitoring. We have already published some work conducting PISA in flow, which combined my existing expertise in PISA, with my growing interest in reactor technologies, but it became apparent that the relatively long timescales for the reactions meant that there were limited advantages over batch synthesis. We therefore looked to speed up the process, which was relatively straight-forward since our all-acrylamide PISA system was ideally suited to Seb Perrier’s ‘ultrafast’ RAFT technology. By using flow-reactors equipped with online monitoring, we were not only able to synthesise a wide range of PISA nanoparticles on short timescales, but also obtain kinetic data despite the short reaction time.

Which polymer scientist are you most inspired by?

From a synthetic perspective, the work being undertaken in Prof Brent Sumerlin’s group encompasses many of the areas I have a keen interest. I am also inspired by Prof Tanja Junkersresearch, since she is at the forefront of work into applying automation and flow chemistry to polymer synthesis.

How do you spend your spare time?

I now have two children under 3, so I spend most of my time running around after them! We spend quite a lot of time hiking in the Peak District and I also like to cook, which has recently expanded into bread making (to varying degrees of success).

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

I’d be a barista with a small coffee shop somewhere sunny.

Read Nick’s full article now for FREE

And if you are interested in reading more about PISA then check out our recent themed collection here


Rapid production of block copolymer nano-objects via continuous-flow ultrafast RAFT dispersion polymerisation

 

graphical abstract

Ultrafast RAFT polymerisation is exploited under dispersion polymerisation conditions for the synthesis of poly(dimethylacrylamide)-b-poly(diacetoneacrylamide) (PDMAmxb-PDAAmy) diblock copolymer nanoparticles. This process is conducted within continuous-flow reactors, which are well suited to fast reactions and can easily dissipate exotherms making the process potentially scalable. Transient kinetic profiles obtained in-line via low-field flow nuclear magnetic resonance spectroscopy (flow-NMR) confirmed the rapid rate of polymerisation whilst still maintaining pseudo first order kinetics. Gel permeation chromatography (GPC) reported molar mass dispersities, Đ < 1.3 for a series of PDMAmxb-PDAAmy diblock copolymers (x = 46, or 113; y = 50, 75, 100, 150 and 200) confirming control over molecular weight was maintained. Particle characterisation by dynamic light scattering (DLS) and transmission electron microscopy (TEM) indicated successful preparation of spheres and a majority worm phase at 90 °C but the formation of vesicular morphologies was only possible at 70 °C. To maintain the rapid rate of reaction at this lower temperature, initiator concentration was increased which was also required to overcome the gradual ingress of oxygen into the PFA tubing which was quenching the reaction at low radical concentrations. Ill-defined morphologies observed at PDAAm DPs close to the worm-vesicle boundary, combined with a peak in molar mass dispersity suggested poor mixing prevented an efficient morphological transition for these samples. However, by targeting higher PDAAm DPs, the additional monomer present during the transition plasticises the chains to facilitate formation of vesicles at PDAAm DPs of ≥300.


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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Polymer Chemistry Author of the Month: Suhrit Ghosh

Suhrit Ghosh was born in 1976 in India. After the completion of his undergraduate education (Chemistry major) at the Presidency College (now University), Kolkata, he was admitted to the integrated PhD program (Chemical Science) at the Indian Institute of Science, Bangalore in 1997. He received his MS degree (Chemistry) in 2000 and continued for PhD until 2005 under the supervision of Professor S. Ramakrishnan. Then he moved to the group of Professor S. Thayumanavan at the University of Massachusetts, Amherst, USA, for postdoctoral studies (2005-2007). Subsequently he worked as an Alexander von Humboldt postdoctoral fellow (2007-2008) with Professor Frank Würthner at the University of Würzburg, Germany. In 2008 he joined the Indian Association for the Cultivation of Science (IACS), Kolkata, India, as an Assistant Professor where he currently holds the position of Professor and Chair of the School of Applied and Interdisciplinary Sciences.

Research interests of his group include supramolecular polymerization of donor-acceptor π-systems, H-bonding driven directional assembly of amphiphilic π-systems/macromolecules and biologically relevant stimuli responsive aggregation of amphiphilic polymers (polydisulfides, polyurethanes). He has about 100 publications in peer reviewed journals and ten PhD students have graduated from his group. He is the recipient of the B. M. Birla Science Prize in Chemistry (2014), JSPS Invitation Fellowship (long term) Japan (2014), SwarnaJayanti Fellowship (2015) from the Department of Science and Technology, Government of India, K. Kishore Memorial Award (2016) from the Society of Polymer Science, India and the Bronze medal (2017) from the Chemical Research Society of India. He has been serving as an Associate Editor for the journal RSC Advances since 2015.

What was your inspiration in becoming a polymer chemist?

I was introduced to Polymer Chemistry by two captivating teachers (Professor Manas Chanda and Professor S. Ramakrishnan) during my Master’s Degree course work in the Indian Institute of Science, Bangalore. Subsequently I had an opportunity to carry out a year-long MS project on Polymer Chemistry under the supervision of Professor S. Ramakrishnan when I started learning more about the subject. From group discussions and seminars in the department, I learnt about the emerging topics (of the time) in Polymer Chemistry such as foldamers, molecular imprinting, conjugated polymers, helical polymers, amphiphilic polymers, supramolecular polymers and so on. I was greatly inspired by such diversity in the field and its interdisciplinary nature connecting chemistry with biology and materials science.

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

Poly(disulfide)s (PDS), although known for long time, lacked structural diversity in the absence of any generally applicable synthetic methodology. Recently we had established a mild step-growth polymerization approach to make linear functional PDS by a facile thiol-disulfide exchange reaction between commercially available 2,2′-dipyridyldisulfide and a di-thiol.  By taking a stoichiometric excess of the first monomer, telechelic PDS could be prepared with the reactive pyridyl-disulfide groups at the chain terminal which could be further functionalized by a functional thiol without disturbing the backbone disulfide groups. This motivated us to extend this approach for the synthesis of hyperbranched PDS, particularly considering the possibility of decorating such hyperbranched polymers with multiple reactive pyridyl-disulfide groups at the periphery for post-polymerization functionalization to produce a range of functional hyperbranched polymers with a fully bio-reducible disulfide backbone. We have exactly demonstrated this in our recent Polymer Chemistry paper and envisage that it might allow the screening of structurally diverse amphiphilic hyperbranched PDS for biological applications such as drug delivery.

Which polymer scientist are you most inspired by?

I am most inspired by Professor E. W. Meijer (Eindhoven University of Technology, The Netherlands), especially because of his pioneering fundamental contribution in the field of supramolecular polymers by connecting supramolecular chemistry and polymer chemistry.

How do you spend your spare time?

I like to cook, spend time with my 10-year-old daughter and socialize with like-minded people.

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

Practising literature and creative writing.

Read Suhrit’s full article now for FREE until 8th May!


Hyperbranched polydisulfides

Disulfide containing polymers have been extensively studied as responsive materials for biomedical applications such as drug delivery, gene delivery, bio-sensing and receptor-mediated cellular uptake due to the possibility of cleaving the disulfide linkage with glutathione (GSH), a tri-peptide overexpressed in cancer cells. While linear and branched polymers containing disulfide groups have been already studied and more recently polydisulfides (PDS) have come to the fore, hyperbranched polydisulfides (HBPDS) were not known. This manuscript for the first time reports a generally applicable methodology for the synthesis of HBPDS by an A2 + B3 condensation approach. The B3 monomer contains three pyridyl-disulfide (Py–Ds) groups while a di-thiol compound serves as the A2 monomer. A polycondensation reaction under very mild reaction conditions produces HBPDS (Mw = 14300 g mol−1Đ = 1.9) with a very high degree of branching (DB) value of 0.8 and more than twenty highly reactive Py–Ds groups present at the terminal or linear unit of a polymer on an average. The reactive Py–Ds groups can be completely replaced by post-polymerization functionalization using a hydrophilic thiol resulting in bio-reducible amphiphilic HBPDS. It produces micellar aggregates in water with a hydrodynamic diameter of ∼80 nm, a low critical aggregation concentration (7.0 μM) and a high dye (Nile red) loading content. The exchange dynamics of these micellar aggregates, studied by fluorescence resonance energy transfer (FRET), reveals practically no inter-micellar exchange after 6 h indicating very high non-covalent encapsulation stability. On the other hand, in the presence of glutathione, the PDS backbone can be degraded resulting in an efficient triggered release of the encapsulated dye. Dye release kinetics strongly depends on the GSH concentration and interestingly with a fixed concentration of glutathione the release kinetics appears to be much faster for the hyperbranched PDS micelle compared to its linear analogue. MTT assay with two representative cell lines indicates that the amphiphilic HBPDS is biocompatible up to 500 μg mL−1 which is further supported by hemolysis assay showing merely 6.0% hemolysis up to a polymer concentration of 500 μg mL−1.


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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Polymer Chemistry Author of the Month: Stefan A F Bon

Professor Stefan A. F. Bon

Stefan A. F. Bon is a full professor in the Department of Chemistry at the University of Warwick in the United Kingdom. He studied chemical engineering at the Eindhoven University of Technology (TUe) in the Netherlands (cum laude, 1989-1993), where he also did his Ph.D. (1993-1998) in the polymer chemistry group of prof.dr.ir. Anton L. German. In April 1998 he moved to the UK  where worked as a post-doctoral research assistant in the group of prof. David M. Haddleton at the University of Warwick (1998-2000). He was appointed as Unilever Lecturer in Polymer Chemistry at the University of Warwick in January 2001. During this period of research he focused on the mechanistic aspects of living radical polymerisation in both homogeneous and heterogeneous systems, including the first ever living radical polymerization performed in emulsion. From 2005 Stefan Bon shifted his research interests from living radical polymerization to supracolloidal chemical engineering. Current research focuses on the design of assembled supracolloidal structures and the synthesis of their colloidal and macromolecular building blocks through combination of polymer chemistry, colloid science, soft matter physics, and chemical engineering. Check out www.bonlab.info for more.

What was your inspiration in becoming a polymer chemist?

Eindhoven University of Technology in the 1990s was a fantastic place for polymer science, especially in the fields of emulsion polymerization and polymer physics and processing. We had captivating teachers, such as Alex van Herk, Anton German, and Piet Lemstra.  I was fascinated by it all as an undergrad student and hooked after my international internship at Nippon Paint where I worked on polymer colloids in the summer of 1992. I grabbed the opportunity to do my PhD on nitroxide mediated polymerizations at the end of 1993. What I love about polymer and colloid science is that you can blend chemistry, with physics, mathematics and engineering, fading out boundaries between classical disciplines.

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

In the mid 2000s we started applying the phenomenon of Pickering stabilization, the concept that particles can adhere to soft deformable interfaces, to mini-emulsion and emulsion polymerization processes. In the last decade we tried to come to a full mechanistic understanding of emulsion polymerization processes in which nanoparticles played the role of molecular surfactants. For the most part we focussed on inorganic nanoparticles, such as clay and silica sols. In 2018/2019 we asked ourselves if Pickering emulsion polymerization would be possible using polymer nanoparticles (10-40 nm), that is nanogels or crosslinked polymer micelles could be used instead. To our delight we found that using nanogels gave us the opportunity to control the morphology of the polymer colloids produced by the Pickering emulsion process. Janus, patchy and armored particles can be made. We wanted to unravel the exact mechanism. The paper in Polymer Chemistry describes a detailed mechanistic study on the effect of inert electrolyte (salt) on the emulsion polymerization process.

Which polymer scientist are you most inspired by?

On passion for emulsion polymerization I would like to mention Bob Gilbert. I know Bob since the mid 1990s, and have great respect for him. I still remember the discussions we had at Santa Margherita Ligure in 1996 on kinetics of radical polymerization and life. I love his mechanistic/kinetic approach to describe scientific concepts and have adopted this as a way of working in my team. On optimism and living larger than life, my former polymer chemistry teacher and friend Alex van Herk, who now works at A*STAR in Singapore. A big thank you to both.

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

Restricting myself to people with an academic career path I would like to mention four: Nick Ballard (POLYMAT, Spain), Athina Anastasaki (ETH Zürich, Switzerland), Stuart Thickett (UTAS, Australia), and Zhihong Nie (Fudan University, China). Why? That is simple, all four are fantastic.

How do you spend your spare time?

My husband and I bought a house in Coventry (UK) a bit over a year ago, and since then the garden is undergoing a transformation to see how many different plants we can put into the space. I think soon we will run out of space and there won’t be a single bit of traditional British lawn left. We like to cook (Chinese/Dutch fusion) , travel, and go to the theatre/concerts. We are looking forward to seeing Pink Martini soon in Birmingham. Will pick up playing the guitar again (haha, and if you wonder what style of music: Julio Iglesias of course!).

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

That is a hard question. Has to be creative and with people for sure. May be something in the area of people communication/management mediation..

Read Stefan’s full article now for FREE until the 31st March!


Effect of the addition of salt to Pickering emulsion polymerizations using polymeric nanogels as stabilizers

Graphical abstract: Effect of the addition of salt to Pickering emulsion polymerizations using polymeric nanogels as stabilizers

Nanogels made from crosslinked block copolymer micelles are used as stabilizers in the Pickering emulsion polymerization of styrene. The effect of the addition of salt, i.e. NaCl, on the emulsion polymerization is studied. It is shown that an increase in ionic strength of the dispersing medium in these polymerizations led to the formation of latexes of larger diameters. Along with an increase in size, the morphology of these polymer colloids changed from Janus to patchy with an increase in number of nanogels adsorbed on the polymer surface, as a function of the salt concentration in water. In particular, at the highest tested ionic strength, ca. 25 mM, fully armored polymeric particles surrounded by a dense layer of adsorbed stabilizing nanogels were formed. Kinetic studies carried out at varying NaCl concentrations suggested that particle formation in the reaction followed a combination of a coagulative nucleation mechanism, characterized by a clustering process of Janus precursors to form bigger aggregates, and droplet nucleation. Preliminary film formation studies on latexes made with n-butyl acrylate as a comonomer indicated the potential of this technique for the production of coherent polymer films which included a substructure of functional nanogels.


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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Polymer Chemistry Author of the Month: Claude St Thomas

Claude St ThomasClaude St Thomas studied chemistry at the École Normale Supérieure, Université d’État d’Haïti, Port au Prince, Haïti. In 2008, he moved to Mexico where he obtained MSc and PhD degrees in polymer chemistry at the Centro de Investigación en Química Aplicada (CIQA) under the guidance of Dr. Ramiro Guerrero Santos. During his PhD studies, he undertook two research stays at the Laboratory of Chemistry and Processes of Polymerization (LCPP), in Lyon, France under the supervision of Prof Bernadette Charleux and Dr. Franck D’Agosto. He designed a novel dual RAFT/NMP chain transfer agent for a tandem polymerization and investigated its use for preparing the self-assembled nanoparticles. This investigation was awarded with the 2015 Rafael Illescas Frisbie prize from the Mexican Chemistry Society as the best PhD thesis. In the same year, he was promoted as a CONACYT research fellow at CIQA.

His research mainly focuses on the preparation of well-defined multiblock copolymers and the development of novel associative polymers featuring stimuli-responsive groups using reversible deactivation radical polymerization (RDRP) techniques. He is also interested in the rheological properties of polymers for applications in coatings, paints, enhanced oil recovery, and water treatment.

What was your inspiration in becoming a polymer chemist?

In my childhood, I was always fascinated by nature. At the beginning, I dreamed about becoming an agronomist. However, my interest for chemistry started in high school by the teachings from chemistry lecturer Sylvain Jean Desir. There, I understood that chemistry is the basis of life. During my MSc and PhD studies I worked with materials of common and daily use and a special interest for polymer chemistry started rising.

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

In our research group, scientific contributions related to the preparation of water-soluble copolymers have been previously published under the supervision of Dr. Enrique Javier Jiménez Regalado using free radical polymerization. In 2014, the “Consejo Nacional de Ciencía y Tecnología” (CONACYT, México) started a new program for addressing solutions to national problems, where young researchers were engaged and assigned to specific projects. Since, I started in my current position in 2015 and inspired by the versatility of the RAFT polymerization technique, my current research work focuses on the development of novel pathways for preparing well-defined water-soluble associative copolymers.

Inspired by the RDRP techniques and their feasibility for synthesizing polymeric materials with unprecedented properties, our recent contribution describes a new strategy for preparing environmentally-friendly water-soluble associative copolymers using the RAFT technique.

Which polymer scientist are you most inspired by?

A group of scientists have impacted my career. I appreciate the discipline, rigor and professional achievements of both Prof Bernadette Charleux and Dr. Franck D’Agosto. Fascinated by RDRP techniques, I am also inspired by three experts in RDRP: Prof Craig J. Hawker, Prof. San H. Thang and Prof. Krzysztof Matyjaszewski. Their publications describing processes for synthesizing polymers with specific characteristics might allow the use of these materials in different industrial applications.

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

Based on application areas of polymeric materials, it would be difficult to mention researchers who will have a big impact on the field. Notwithstanding, I select Dr. Francesco Picchioni (University of Groningen). His research on the development of chemical materials for application in Enhanced Oil Recovery (EOR) displays great interest and could impact the field. For these researches, I am also impressed by the research works of Dr. Michael F. Cunningham (Queens University) and Sébastien Perrier (University of Warwick)

How do you spend your spare time?

Outside of professional activities, I enjoy spending time with my family (wife and four year-old daughter-Nicole) and visiting natural places. My favorite sport is soccer, so I enjoy playing it with friends. I also enjoy playing guitar and reading about new scientific developments and culture.

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

Probably an agronomist due to my passion for natural sciences, because it was my first dream.

Read Claude’s full article now for FREE until the 31st January!


Preparation of hydrophobically modified associating multiblock copolymers via a one-pot aqueous RAFT polymerization

Graphical abstract: Preparation of hydrophobically modified associating multiblock copolymers via a one-pot aqueous RAFT polymerization

We describe an efficient strategy for the preparation of hydrophobically associating multiblock copolymers using the RAFT technique. Polymerization reactions were carried out by a one-pot aqueous RAFT polymerization at 70 °C using a symmetrical trithiocarbonate as a chain transfer agent (CTA) in aqueous media. The macroRAFT polyacrylamide (PAM) was synthetized and chain extended by polymerization of N,N′-dihexylacrylamide (DHAM) and acrylamide (AM), respectively. The resultant polymers were intensely characterized by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) spectroscopy, diffusion-ordered spectroscopy (DOSY), Fourier transform-infrared (FT-IR) spectroscopy and rheology. The structure and insertion of a hydrophobic block (PDHAM) into the backbone were carefully demonstrated. The rheological measurements confirmed the effect of the hydrophobic block number on the viscosity of polymers at different concentrations and the formation of a reversible physical network of entangled polymers in aqueous media. Moreover, the incorporation of the hydrophobic block (PDHAM) was established by the oscillatory measurement.


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. 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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Polymer Chemistry Author of the Month: Christina Chai

Christina Chai obtained her BSc (Hons) from the University of Canter­bury, Christchurch, New Zealand and her PhD in organic chemistry from the Research School of Chemistry, Australian National University, Canber­ra under the mentorship of the late Professor Athel Beckwith, FRS. Following her PhD, she was awarded a Samuel and Violette Glasstone Research fellowship at the University of Oxford, UK. This was followed by a Faculty position in the Department of Chemis­try, Victoria University of Wellington, NZ (1991-1993) and the Department and Research School of Chemistry, Aus­tralian National University (1994-2004) where she rose to the rank of a Reader. In 2005, Christina moved to Singapore to establish a research programme on synthetic and polymer chemistry at the then newly founded Institute of Chemical and Engineering Sciences, Agency for Science Technology and Research (A*STAR). She returned to a life in academia in 2011 at the Department of Pharmacy, National University of Singapore where she has held many administrative positions. She is currently Professor and the Head of the Department of Pharmacy. Although her major research interest is on bioactive compounds, she moonlights in polymer chemistry with special interest in biomimetic materials.

What was your inspiration in becoming a scientist who works with polymers?

My PhD training was in the area of free radical chemistry with one of the free radical ‘’gods’’, the late Professor Athel Beckwith. At that time, a superb team of chemists in CSIRO Australia had developed the RAFT process which was based on the principles of radical chemistry, and I was fascinated with the numerous possibilities of this process in creating new materials. Although this fascination remained after my PhD studies, I did not have the opportunity to work with polymers until I moved to A*STAR Singapore. I continue to be intrigued with clever ways of designing functional polymers for various applications.

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

When I first joined NUS, I received a grant that allowed me to work on biomimetic materials, specifically mussel-inspired coatings. I was intrigued with the claims that polydopamine (PDA) is a universal coating material, and was amazed with the reported applications of polydopamine. If one read and believed all the literature, one would imagine that PDA is the answer to all our material needs. As we worked to develop PDA functional coatings, we were hampered by the lack of information on the structure of PDA. We wanted to improve the properties of PDA but how do we improve a mystery material? So we set out to understand the oxidation chemistry of dopamine, and the process of coating and of course, to attempt to elucidate the structure of PDA. I was fortunate that my PhD student at that time, Lyu Qinghua was so obsessed with this mystery that he refused to submit his thesis until he knew the answer. I am not convinced that we have completely solved the mystery (although I did manage to persuade the student to submit his thesis) but I believe that we have made significant progress in the structural elucidation. The answer is just around the corner!

Which polymer scientist are you most inspired by?

In view of my training as a free radical chemist, I was most interested in the ability to control polymer synthesis through living free radical polymerisation methods such as ATRP and RAFT. I personally know Professor San Thang, now of Monash University, who is one of the co-inventors of RAFT, and his life story and his humility despite his successes is one of my inspiration. Professor K. Matyjaszewski, the guru of ATRP and Professor Craig Hawker, with his fascinating designs of functional polymers are also heroes in my eyes.

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

Professor Molly Stevens from Imperial College London is a name that comes to mind as her research on materials for biomedical applications will be a game changer.

How do you spend your spare time?

I love reading and travelling. I read fiction and non-fiction for pleasure. My love for travel is not about visiting places of interest but to immerse myself in a different environment and culture.  Although I am an introvert, I am interested in people-watching. People are fascinating subjects for study!

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

A doctor, a nun or a scientist – This is what I would say when I was a child when people asked me what I wanted to be when I grew up. As I doubt that I would be religious enough to qualify as a nun, this just leaves being a doctor as my alternate profession that I would choose. However I love being a scientist! I constantly worry about not having enough funds to support my research. My dream is to win the lottery so that I can support my research for the rest of my career…

Is the end in sight for the structural analysis of polydopamine? What important questions remain to be answered?

Yes, I believe that the end is in sight for the structural analysis of polydopamine. I believe that fundamental studies are important if we want to advance the applications. Without knowing the structure, how do we improve the properties of the material? There are still gaps in PDA technology that needs to be addressed. For example, one would need to know how to reproducibly control the thickness and homogeneity of the material; how to reduce the coloration and improve stability…. There is so much that we do not yet know.

 

Read Christina’s full article now for FREE until the 21st December!


Unravelling the polydopamine mystery: is the end in sight?

Graphical abstract: Unravelling the polydopamine mystery: is the end in sight?

Despite the prominence of polydopamine (PDA) in the field of polymer and materials chemistry since it was first reported by H. Lee, S. M. Dellatore, W. M. Miller and P. B. Messersmith, Science, 2007, 318, 426–430, the structure of PDA has been an unresolved and contentious issue. Current consensus favors polymers derived from the cyclized intermediate 5,6-dihydroxyindole (DHI). In this work, compelling evidence for the possible structure of PDA is shown via detailed mass spectroscopic studies using deuterium-labeled dopamine (DA) precursors. More specifically, the major component of PDA is shown to derive from dopaminochrome (DAC) and uncyclized DA components. One major intermediate, seen at m/z 402, is characterized as a combination of benzazepine + DAC + 2H-pyrrole, which has a chemical formula of C23H20N3O4. Furthermore, DAC forms stable complexes with DA, and is a key control point in the polymerization of PDA. The decay of DAC into DHI is a relatively slow process in the presence of excess DA, and plays a smaller role in PDA formation. This study shows the covalent connectivity in PDA from the starting DA monomer, and represents an important advance in elucidating the structure of PDA.


About the Webwriter

Simon HarrissonSimon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based in the Laboratoire des IMRCP in Toulouse. 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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Polymer Chemistry Author of the Month: April Kloxin

April M. Kloxin, Ph.D., is an Associate Professor in Chemical & Biomolecular Engineering and Materials Science & Engineering at the University of Delaware (UD) and a member of the Breast Cancer Research Program at the Helen F. Graham Cancer Center and Research Institute in the Christiana Care Health System.  She obtained her B.S. and M.S. in Chemical Engineering from North Carolina State University and Ph.D. in Chemical Engineering from the University of Colorado, Boulder, as a NASA Graduate Student Research Program Fellow.  She trained as a Howard Hughes Medical Institute postdoctoral research associate at the University of Colorado before joining the faculty at UD in 2011. Her group aims to create unique materials with multiscale property control for addressing outstanding problems in human health. Her research currently focuses on the design of responsive and hierarchically structured soft materials and development of controlled, dynamic models of disease and regeneration.  Her honors include the Biomaterials Science Lectureship 2019, ACS PMSE Arthur K. Doolittle Award 2018, a Susan G. Komen Foundation Career Catalyst Research award, a NSF CAREER award, and a Pew Scholars in Biomedical Sciences award.

What was your inspiration in working with polymers?

I have always enjoyed building things and had a desire to use those skills to help people.  I discovered my passion for using chemical approaches to build soft polymeric materials possessing unique and useful properties as an undergraduate and Master’s student at North Carolina State University (NCSU).  At NCSU, I had the opportunity to work in a collaborative environment with many extraordinary friends and colleagues having great polymer science and engineering expertise, including my MS thesis advisors Profs. Rich Spontak and Stuart Cooper.  This experience helped me understand the connection between molecular design and synthetic approaches for building polymeric materials with specific properties for a desired application.  I had the opportunity to fully realize and direct this passion working at the interface between polymeric materials and biological systems under the outstanding advisement and mentorship of Prof. Kristi Anseth at the University of Colorado, Boulder, for my Ph.D. and with the many remarkable researchers in her group and at the University.


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

From a biological perspective, my group has a focus on understanding how changes in the structure, mechanical properties, and compositions of tissues in the human body that occur upon injury influence the function and fate of key cells in healing and disease.  In this context, we have been interested in building synthetic mimics of these complex systems and processes, and we wanted to establish simple yet effective approaches for controlling the density and stiffness of soft materials when and where desired for hypothesis testing.  In the Polymer Chemistry manuscript, we were inspired by the work of Prof. Matt Becker (Duke University) amongst others demonstrating how the rate of formation of water-swollen polymer networks, hydrogels, could be used to control defect formation, network heterogeneity, and thereby the mechanical properties of the resulting materials.  We hypothesized that the rate-based control of properties that others observed with catalyzed step growth reactions was translatable to a photo-polymerized system, affording the implementation of a variety of photochemical controls (e.g., wavelength, intensity, time).  In particular, by selecting a wavelength of light that was not centered at the maximum absorption of the photoinitiator, we were better able to control the rate of photopolymerization with an accessible bench-top visible light LED system and thereby defect formation.  We then saw an opportunity to exploit dangling-end defects that were generated with this rate-based approach to increase crosslink density and ‘stiffen’ these materials with a secondary photopolymerization.  We are excited about the potential that this light-triggered rate-based approach for controlling mechanical properties of polymer networks has for a number of applications, including our on-going studies of cell response to matrix stiffening.


Which polymer or materials scientists are you most inspired by?

Oh, there are so many! I am especially inspired by the work and leadership of Prof. Paula Hammond (MIT) and Prof. Kristi Anseth, who continue to blaze trials at the interface between polymers, materials, and biology to solve complex problems, and Prof. Chris Bowman (University of Colorado, Boulder) and the late Prof. Charlie Hoyle (University of Southern Mississippi), who have pioneered the use of light-triggered step growth reactions for creating polymeric materials with diverse and robust properties.


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

It is an exciting time in polymer chemistry with many excellent researchers working from different perspectives to advance not only the field of polymer chemistry, but also to make fundamental breakthroughs that have an impact in biology, medicine, and energy.  Selecting just a few is difficult in this context.  A few that come to mind at the moment whose work I find particularly inspiring are Prof. Aaron Esser Kahn (University of Chicago) in biomolecular design of polymeric materials for rewiring the immune system, Prof. Dominik Konkolewicz (Miami University Ohio) in bioconjugations and dynamic covalent chemistries with polymeric materials, Prof. Rachel A. Letteri (University of Virginia) in peptide-polymer conjugates for multi-scale and dynamic properties, and my own new colleague Prof. Laure Kayser (University of Delaware) in conducting and semiconducting polymers.


How do you spend your spare time?

I enjoy making things, from designing materials at work to preparing satisfying meals in the kitchen at home.  Breakfast foods are my favorite, and I have different recipes that I continue to hone on weekends for quick meals during the week.  I also love being outside walking, hiking, or running with my friends or my husband and our two sons, particularly in the beautiful early autumn weather we currently are having.


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

My obsession with the complexity of biological systems and improving human health would keep me in science and engineering, whether in molecular biology or bioinformatics or more applied in medicine.

 

Read April’s recent Polymer Chemistry article now for FREE until 31st October!


Rate-based approach for controlling the mechanical properties of ‘thiol–ene’ hydrogels formed with visible light

 

The mechanical properties of synthetic hydrogels traditionally have been controlled with the concentration, molecular weight, or stoichiometry of the macromolecular building blocks used for hydrogel formation. Recently, the rate of formation has been recognized as an important and effective handle for controlling the mechanical properties of these water-swollen polymer networks, owing to differences in network heterogeneity (e.g., defects) that arise based on the rate of gelation. Building upon this, in this work, we investigate a rate-based approach for controlling mechanical properties of hydrogels both initially and temporally with light. Specifically, synthetic hydrogels are formed with visible light-initiated thiol–ene ‘click’ chemistry (PEG-8-norbornene, dithiol linker, LAP photoinitiator with LED lamp centered at 455 nm), using irradiation conditions to control the rate of formation and the mechanical properties of the resulting hydrogels. Further, defects within these hydrogels were subsequently exploited for temporal modulation of mechanical properties with a secondary cure using low doses of long wavelength UV light (365 nm). The elasticity of the hydrogel, as measured with Young’s and shear moduli, was observed to increase with increasing light intensity and concentration of photoinitiator used for hydrogel formation. In situ measurements of end group conversion during hydrogel formation with magic angle spinning (MAS 1H NMR) correlated with these mechanical properties measurements, suggesting that both dangling end groups and looping contribute to the observed mechanical properties. Dangling end groups provide reactive handles for temporal stiffening of hydrogels with a secondary UV-initiated thiol–ene polymerization, where an increase in Young’s modulus by a factor of ∼2.5× was observed. These studies demonstrate how the rate of photopolymerization can be tuned with irradiation wavelength, intensity, and time to control the properties of synthetic hydrogels, which may prove useful in a variety of applications from coatings to biomaterials for controlled cell culture and regenerative medicine.

 


About the Webwriter

Simon HarrissonSimon Harrisson is a Chargé de Recherche at the Centre National de la Recherche Scientifique (CNRS), based in the Laboratoire des IMRCP in Toulouse. 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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