Polymer Chemistry Blog

Dr. Sci. Georges M. Pavlov studied physics at the State Leningrad University and received his master degree there in 1965. After two years working as a professor of physical sciences in Algeria, GMP began his scientific career at the Institute of Macromolecular Compounds of the USSR Academy of Sciences, where in 1975 he received his Ph.D. with V. N. Tsvetkov and S. Ya. Magarik for investigation on flow birefringence and hydrodynamic solution properties of homologous series of grafted copolymers. At the invitation of prof. V.N. Tsvetkov in 1977 GMP returned to the Department of Physics of the Leningrad State University, where later he was awarded a Dr. Sci. degree for his research on molecular hydrodynamics and optics of natural and synthetic polysaccharides. Pavlov has trained many undergraduates and doctoral students. His research activities are documented in over 200 scientific papers, focused on functional synthetic and biological macromolecular compounds, their properties, establishing the relationship between the chemical structure and corresponding properties of macromolecules. This includes investigation of polyelectrolytes in an extremely wide range of ionic strengths; macromolecules of complex topology (brush-shaped, star-shaped, dendrimer, hyperbranched, associated and supramolecular structures); influence of molecular characteristics of polymers on the properties of their films; methodology of molecular hydrodynamics (velocity sedimentation, translational diffusion, viscous flow of dilute solutions) and birefringence of polymer solutions and polymer films. During his career, he worked for a long time as an invited researcher in the Universities and Scientific Centers of UK, France, the Netherlands and Germany. Currently he is a Leading Researcher in the Institute of Macromolecular Compounds, Russian Academy of Science.

 What was your inspiration in becoming a polymer scientist?

When I was in high school, it was the time of the first sputniks/satellites (not to be confused with a vaccine), there was a lot of talk about the peaceful use of atomic energy. At school, I was more successful in natural science subjects (chemistry and physics) and mathematics. In the end, my choice fell on the Department of Physics of Leningrad University. At the University, when the choice of specialization came, I chose the Cathedra of Polymer Physics, at that time it was the only one in the USSR.

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

In collaboration with our chemist colleagues, at the Institute of Macromolecular Compounds, we investigate water-soluble amphiphilic polymer systems capable of retaining and transferring biologically active substances / drugs into a living organism. Such systems are prone to intra- and intermolecular association. It turned out that this ability can be detected by a well-known (routine ?!) method – by measuring the viscosity of dilute polymer solutions. However, two types of plots/equations of Huggins and Kremer should be applied in the interpretation of experimental data. So the tediousness/scrupulousness allowed this study to be done. Our recommendation is to use both plots in all cases of treating the viscometric data.

Which polymer scientist are you most inspired by?

This is a difficult question because we are known to stand on the shoulders of giants. With regard to polymer science, in particular the molecular physics of polymers, the pioneering fundamental work was done by Werner Kuhn, Paul Flory, Hermann Staudinger, Peter Debye. This list is far from complete, and the names can be arranged in a different order. But I would like to cite the name of Viktor N. Tsvetkov, who began to deal with issues of experimental molecular physics of polymers in the USSR, in particular, flow birefringence of polymer solutions at the beginning of the 40s of the 20th century. Later (in 1958), he organized the first in the USSR Cathedra of Polymer Physics at the Department of Physics of Leningrad University, which was equipped with a whole range of self-made precision devices for studying the molecular properties of macromolecules in solutions and films. His approach was to study the homologous series of different polymers using a complex of molecular hydrodynamics and optics methods, usually 4-5 different methods were used simultaneously. This Cathedra still exists under the name: Molecular Biophysics and Polymer Physics.

How do you spend your spare time?

Traveling, listening to different kinds of music.

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

Choosing a different path, I would choose something related to creativity. For example, I would to be a baker, but in France. However this extrapolation back in time is too long to be reliable and imaginable enough.

Read Georges’ full article now for FREE until 25 July

Mona Semsarilar

Mona Semsarilar completed her MSc. in 2006 in physical chemistry under the supervision of Prof. E. Yilmaz (EMU, Cyprus). She continued her studies by joining Prof. S. Perrier’s team at the University of Leeds and earned her PhD from the University of Sydney in 2010, working on the synthesis of hybrid materials based on cellulose. She then moved to the University of Sheffield (UK) to work on Polymerisation-Induced Self-assembly (PISA) under the supervision of Prof. S. P. Armes (FRS). In 2015 she was recruited by the French national research organization (Centre National de la Recherche Scientifique – CNRS) as a research scientist based in the European Institute of Membranes (Institut Européen des Membranes – IEM) in Montpellier. In 2019, she received her habilitation from the University of Montpellier. Her research team looks into the preparation of materials primarily for applications in membrane and separation science using synthetic chemistry tools. Her current research focus on the design, synthesis and self-assembly of functional block copolymers, polymer-peptide conjugates, hybrid materials based on natural polymers, Metal Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs).

What was your inspiration in becoming a polymer chemist?

As a teenager, I was a big fan of Marie Curie as she was one of the only female figures in the world of Science and Technology. Also, my maternal great grandfather was a herbalist and I enjoyed going through his books and notes that my grandfather had inherited. I was fascinated by the hand-made illustrations and spent hours flicking through the fragile books and trying to copy the pictures! However, becoming a polymer chemist was just fortuitous. It just happened that I got a good offer to study polymer chemistry. I am deeply grateful for this coincidence as it paved my way into joining a family of great scientists that are not only good in what they do but also very kind and supportive individuals.

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

I have been working on the concept of Polymerisation-Induced Self-Assembly (PISA) since 2010. In the early years, we were mainly looking into two factors influencing the in-situ self-assembly; chemical functionalities in the shell-forming block and the solvophilic- solvophobic block ratios. One of our early works on galactose-coated nanoparticles prepared through PISA showed that hydrogen bonding played a crucial role in pushing the morphology towards higher orders. To explore this further, we wanted to use moieties that could provide a variety of supramolecular bonds and for this, peptides were the obvious choice. Now we have a library of monomers containing short sequences of peptides with ability to form hydrogen bonding and pi-pi interactions. Our first paper using these monomers, recently published in Macromolecules, demonstrates that presence of self-assembling peptides in the shell-forming block controls the self-assembly and is the main drive in the formation of interconnected fibrous networks. These results made it very clear that the presence of only few units of self-assembling peptide monomers were enough to push the self-assembly towards higher orders and form the unprecedented structures reported. For us the next obvious step was to see if the same effect could be seen once the self-assembling peptides were placed in the core of the particles, which is the subject of investigation in the current article.

Which polymer scientist are you most inspired by?

I have to say my two mentors (Prof. Perrier and Prof. Armes) have been a great source of inspiration for me. They are both brilliant minds, great scientists as well as very good managers. Their dedication and hard work towards science as well as their approach in managing their research team are admirable. They have a special way of making junior people fall in love with the science they do and create a sense of loyalty towards them and their team that is exceptional.

How do you spend your spare time?

Spare time?! What is spare time?!! Being mother of an energetic three years old does not leave any time to be spared!!! If by any chance I get a bit of time to myself (mainly while commuting) I would think chemistry! However, in the olden days (as Peppa Pig would say!) I used to enjoy reading.

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

I quite enjoy fine manual activities that require attention to details and precise skills. If not designing and making molecular structures, I would have enjoyed being a surgeon, tailor, carpenter or a silversmith. I also have a keen sense of observation and enjoy solving puzzles. So being a spy or a detective could have been the other options.

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 (M_n) 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 (M_w) 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 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

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 20^th 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

Nick 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 Junkers’ research, 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

 

Sam Parkinson, Stephen T. Knox, Richard A. Bourne and Nicholas J. Warren

Ultrafast RAFT polymerisation is exploited under dispersion polymerisation conditions for the synthesis of poly(dimethylacrylamide)-b-poly(diacetoneacrylamide) (PDMAm_x–b-PDAAm_y) 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 PDMAm_x–b-PDAAm_y 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.