Volume 48 Issue 5

October 2020

Special Issue for 100 Years of Polymer Science

From the Editor

Dear readers of the Hacettepe Journal of Biology and Chemistry,

The year 2020 marks the 100th anniversary of a milestone paper published in 1920 by Hermann Staudinger. He introduced the groundbreaking hypothesis of the existence of long chain molecules, formed by a large number of covalently linked monomeric units. This and related papers can be considered as a beginning of the field of macromolecular chemistry and polymer science.
To celebrate the 100th Anniversary of the Polymer Science, Hacettepe Journal of Biology and Chemistry has invited Prof. Dr. Olgun Güven, who is the leading Turkish scientist in polymer science and engineering as a guest editor to prepare this special issue to combine the insights of the researchers working on this area in the form of reviews, trends, or perspectives on the current, past and future developments in macromolecular chemistry. I would like to thank all contributors for making this issue possible. These contributions have been made available in 'open access' format and we invite you to explore these perspectives on what the future of the field might hold.

Prof. Dr. Adil Denizli

100 Years of Polymer Science

On June 12, 1920 Hermann Staudinger, an organic chemist working at the Swiss Federal Institute of Technology in Zurich published a paper titled “Über Polymerisation” that have revolutionized chemistry1. Before 1920 the chemistry community believed that very high molecular weights of certain compounds was the result of formation of molecular aggregates termed as colloids. Staudinger strongly disagreed on this colloidal explanation and said that appearently high molecular weight compounds such as rubber, cellulose, etc. were in fact composed of a series of smaller molecules bonded to each other with covalent bonds, proposing that these are macromolecules. But this was in total contradiction with the scientific opinion of those times. Even the Nobel Laureates Emil Fischer (1902) and Heinrich Otto Wieland (1927) were in complete disagreement of Staudinger’s theory of high molecular weights. Skepticism of Wieland was evident in his advise to Staudinger2: “Dear Colleague, abandon your idea of large molecules, organic molecules with molecular weights exceeding 5000 do not exist. Purify your products such as rubber, they will crystallize and turn out to be low molecular weight compounds.” Staudinger did not step back and after his paper “On Polymerization” in another paper on hydrogenation of natural rubber published in 1922 he used the term “macromolecule”. Despite heavy opposition and even sarcasm of his colleagues Staudinger completely quit his traditional field of research and to focus exclusively on polymer research he moved to the University of Freiburg in 1926 where he remained for the rest of his career, until his retirement in 1951. Staudinger wrote in his memoirs: “Those colleagues who were aware of my early publications in the field of low molecular weight chemistry asked me why I decided to quit these beautiful fields of research and why I devoted myself to such disgusting and ill-defined compounds such as rubber and synthetic polymers which are in view of their properties were referred to as grease chemistry.”

Over the years however, Staudinger provided ample experimental evidence by investigating the reactivity of rubber and cellulose and using viscosimetry to measure molecular weights. The concept was slowly acccepted in the late 1920s and early 1930s. It was only in 1935 that Faraday Society accepted the macromolecular concept. He founded the first polymer chemistry journal “Die Makromolekulare Chemie” (today’s Macromolecular Chemistry and Physics) in 1940. Staudinger’s research was published in more than 800 publications. He summarized his research in his autobiography “Arbeitserinnerungen” published in 1970. His collected Works entitled “Das wissenschaftliche werk von Hermann Staudinger” were edited by his wife Magda Staudinger and published between 1969 and 1976. His decades long effort in developing and promoting his concept of polymers was honored in 1953 when he received the Nobel Prize in Chemistry “for his discoveries in the field of polymer chemistry”. The father of polymer chemistry died on September 8, 1965.

On the occasion of the anniversary of 100 years of polymer science various events and activities have been planned and organized in the World in 2020 via National, International Meeetings or Conferences which were unfortunately shadowed by the COVID-19 pandemic restrictions. Special issues of leading polymer science journals have been dedicated to celebrate this important event to look back at the past, view the present and look ahead to the future. It is an honor for us to publish this special issue of Hacettepe Journal of Chemistry and Biology through the initiative of Prof. Adil Denizli, editor-in-chief of the journal to commemorate Staudinger’s landmark paper. As the guest editor of this issue I am very grateful to internationally renowned Turkish polymer scientists who acccepted our invitation to present their current research in polymer science contributing to this special issue. The list of contributors to this issue is by no means exhaustive, size limitation of the volume bounded are hands to invite more scientists.

We hope that this special issue will be a stimulus for the Turkish scientific community for furthering this exciting subject in the second century of polymer science.

I would like to conclude by referring to the following statement made by Lord Alexander Todd, Nobel Laureate 1957: “I am inclined to think that the development of polymerization is, perhaps, the biggest thing that chemistry has done, where it has the biggest effect on everyday life”.

Prof. Dr. Olgun Güven
Ayvalık, 22 September 2020

  1. H. Staudinger, “Über Polymerisation” Ber. Dtsch. Ges., 53, 1920, 1073-85.
  2. R. Mülhaupt, “Herman Staudinger and the Origin of Polymer Chemistry”, Angew. Chemie Int. Ed., 43, 2004, 1054-63.

Synthesis of Polymer Brushes by Surface-Initiated Controlled/Living Free Radical Polymerization Techniques

The surface modifications are necessary to alter the inherent surface physical/chemical properties of materials in terms of adhesion, wettability, friction, biocompatibility etc. for using in textile, electronic and biomedical industries. Surface modifications are usually made by grafting of polymer brushes to the solid substrates. The grafting process allows controlling and manipulation of surface properties without changing the chemical structure of polymers. Besides their chemical structures, grafting density of polymer brushes and average distance between the polymer chains attached to the surface are also important parameters, affecting the intended use of the grafted materials. Synthesis of functional polymer brushes is generally carried out by one of surface-initiated controlled/living free radical polymerization techniques, namely Atom Transfer Radical Polymerization (ATRP), Nitroxide-Mediated Polymerization (NMP), Photoiniferter-Mediated Polymerization (PIMP) and Reversible Addition-Fragmentation Chain Transfer Polymerization (RAFT). This review reports the strategies of these techniques for generating polymer brushes and summarizes the applications of polymer brushes in multiple fields.

395 - 405
Micro and Nanogels for Biomedical Applications

Micro and nano hydrogels developed from natural and synthetic polymers have garnered great deal of attention in sci- entific and industrial realms due to their higher surface area, degree of swelling and active material loading capacity, softness and flexibility, as well as their similarity to natural tissues. Particularly, biocompatible, non-toxic, and biodegradable micro/nano vehicles with tailor made design and functionalization facilitates their use with excellent feasibility for a variety of biomedical applications such as tissue engineering, bioimaging and drug delivery. However, these platforms require rational design and functionalization strategies to cope with barriers of in vivo environment to pass into clinical use. Firstly, an ideal carrier should be biocompatible, and capable of evasion from immune elimination, specifically target at desired sites and sustainably release the therapeutic cargo in response to microenvironment conditions. Despite the few setbacks in micro/nano vehicle design and several successful formulations translated to clinical use and majority of the carries are yet to achieve complete success for all biological criteria. In this review, design and functionalization strategies of micro and nanogels have been summarized. Also, the recent progress in biomedical applications of microgels and nanogels have been outlined with a primary focus placed on drug and biomolecule delivery applications.

407 - 424
Polyurethanes: Design, Synthesis and Structure-Property Behavior of Versatile Materials

Polyurethanes are one of the most important classes of polymeric materials. This is mainly due to the availability of a very large number of inherently different starting materials that allows the design and synthesis of polyurethane based materials with a wide range of properties for numerous applications. In this short review, important physical and chemical factors and parameters that have a significant effect on the properties of polyurethanes are discussed. Critical contribution of hydrogen bonding on the structure-morphology-property behavior of these materials was emphasized by both experimental data and molecular simulation studies. Influence of the chemical structures, solubility parameters and molecular weights of the soft and hard segments on morphology and properties were discussed. Important issues regarding the reaction chemistry, synthetic method used and thermal history on structure and performance of polyurethanes were explained. We hope this article, which is prepared to celebrate the 100th anniversary of Polymer Science, will be useful to those who are newcomers to the field, but also to the experienced researchers to better understand the structure-property behavior of polyurethanes and tailor-design novel structures for various applications.

425 - 445
Industrial Applications of Superhydrophobic Coatings: Challenges and Prospects

The use of the superhydrophobic coatings and materials in industry is not satisfactory after the intensive activity in research laboratories in the last two decades. We discussed the reasons for this adverse situation under several topics in this review article. The most important issues are the insufficient mechanical resistance and inevitable contamination of the SH surfaces under outdoor conditions, resulting in short useful life-time. The fabrication of a SH surface requires a rough structure with tiny textures on it and this frail framework has a poor mechanical resistance. The topics of superfluous production of small scale and expensive SH surfaces, the difficulty to obtain transparent and also self-healing SH surfaces, the inefficient anti-icing applications of the SH coatings are also discussed.

447 - 457
Electrospun Nanofibers for Wound Dressing and Tissue Engineering Applications

Electrospinning has received tremendous attention in the fabrication of nanofibrous scaffolds over recent years and employed in different biomedical applications because of their biomimetic nature. Especially, the electrospun nanofibers exhibit several beneficial features including natural extracellular matrix (ECM), interconnected pores, large surface area, ease of functionalization and mechanical performance that holds huge importance in influencing the cell adhesion, differentiation and proliferation behaviour. To date, acknowledging the wide range of beneficial features, the electrospun nanofibers have been used in wound dressing and tissue engineering applications. This review summarizes various efforts have been made in these areas with several representative examples indicating use of various materials and approaches. Further the concerns for future direction regard to clinical phase transfer has been discussed.

459 - 481
Radiation-Grafted Polymer Electrolyte Membranes for Fuel Cells

Fuel cells are one of the most efficient energy conversion systems to produce electricity. A solid ion-conducting polymer membrane is employed as both separator and electrolyte for polymer electrolyte membrane fuel cells and anion-exchange membrane fuel cells. Radiation-induced graft polymerization is a versatile method for the fabrication of low-cost alternatives to commercial polymer membranes. In this method, typically a base polymer is exposed to ionizing radiation which generates active radical sites within the polymer substrate. Then a suitable vinyl monomer is polimerized on these active sites to form a graft copolymer. Finally, a subsequent chemical treatment is performed to introduce hydrophilic groups to hydrophobic polymer backbone so that an ion conducting membrane is formed. There are various studies about the influence of radiation grafting parameters on membrane properties. Moreover, the favorable fuel cell relevant and polarization properties of such radiation-grafted membranes were reported. Thus, radiation-grafted polymer membranes are one of the significant low-cost alternatives for fuel cells. This review focuses on the preparation, characterization of fuel cell relevant properties and fuel cell performance of radiation-grafted membranes.

483 - 506
Self-Healing and Shape-Memory Hydrogels

Hydrogels are soft and smart materials with great similarity to biological systems. In the past decade, a significant progress has been achieved to produce mechanically strong and tough hydrogels. Another major challenge in gel science is to generate self-healing and shape-memory functions in hydrogels to extend their application areas. Several strategies have been developed to create self-healing ability in hydrogels by replacing the chemically cross-linked polymer network with a reversible one. Moreover, a combination of strong and weak physical cross-links was used to produce hydrogels with both self-healing and shape-memory behavior. In this review, I present recent developments in the field of self-healing and shape memory hydrogels by mainly focusing our achievements.

507 - 525
Stimuli-Responsive Polymers Providing New Opportunities for Various Applications

Stimuli-responsive polymers significantly change their physical or chemical properties when there is a small change in the conditions of their environments. Depending on the changes on conditions, they can self-assemble to form various nanosized structures having important usages in different fields. In this review, we report an analysis of some of the recent literatures on the basic subjects such as the architectures of different environmentally sensitive polymers, their classifications according to susceptibility and applications in various areas. During the last two decades, there have been great reports in the strategies for the preparation of novel stimuli-responsive polymers and/or polymeric materials which are suitable for various applications including materials science, nanotechnology, biotechnology, colloid and surface science, etc. In order to make this very broad polymer type more understandable to readers, basic concepts/topics are generally schematized. Furthermore, the strategies that can be followed in the production of these materials are tried to be given at a sufficient level.

527 - 574
Molecular Imprinting Technology for Biomimetic Assemblies

The term biomimetic can be simply defined as the examination of nature. The scientist inspired from the enormous diversity of nature to solve human problems or facilitate the daily life by mimicking natural models, systems and elements especially in biomedical and therapeutic applications to make better drugs, artificial organs, sensing instruments etc. Biological recognition elements like proteins, antibodies, enzymes, DNA, lectins, aptamers, cells and viruses have been heavily used to ensure specificity in such applications in spite of their lack of stability and reusability. However, in the last two decades molecularly imprinted polymers, MIPs, have been synthesized as an alternative to mimic natural biological interactions for a broad spectrum of templates by means of coordinating functional monomers around template in the presence of cross-linker. This review will outline the broad contours of biomimetics prepared by molecular imprinting techniques and their practical applications in the separation techniques, tissue engineering applications, biomimetic surfaces, sensors, artificial membranes and drug delivery systems.

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