Responsive polymers for analytical applications: A review

Stimuli-responsive polymers are capable of translating changes in their local environment to changes in their chemical and/or physical properties. This ability allows stimuli-responsive polymers to be used for a wide range of applications. In this review, we highlight the analytical applications of stimuli-responsive polymers that have been published over the past few years with a focus on their applications in sensing/biosensing and separations. From this review, we hope to make clear that while the history of using stimuli-responsive polymers for analytical applications is rich, there are still a number of directions to explore and exciting advancements to be made in this flourishing field of research.     

Analytical characterization of polymers used in conservation and restoration by ATR-FTIR spectroscopy

In the last few decades many new polymers have been synthesized that are now being used in cultural heritage conservation. The physical and chemical properties and the long-term behaviors of these new polymers are determined by the chemical composition of the starting materials used in their synthesis along with the nature of the substances added to facilitate their production. The practical applications of these polymers depend on their composition and form (foam, film, sheets, pressure-sensitive adhesives, heat-seal adhesives, etc.). Some materials are used in restoration works and others for the exhibition, storage and transport of works of art. In all cases, it is absolutely necessary to know their compositions. Furthermore, many different materials that are manufactured for other objectives are also used for conservation and restoration. The technical information about the materials provided by the manufacturer is usually incomplete, so it is necessary to analytically characterize such materials. FTIR spectrometry is widely used for polymer identification, and, more recently, ATR–FTIR has been shown to give excellent results. This paper reports the ATR-FTIR analysis of samples of polymeric materials used in the conservation of artworks. These samples were examined directly in the solid material without sample preparation.     

Progresses on electrospun metal–organic frameworks nanofibers and their wastewater treatment applications

Metal–organic frameworks (MOFs) have been proven to be outstanding adsorbent materials which possess excellent pollutant removal performances in wastewater treatment. However, MOFs consumption, loss, or blockage in reactor pipelines as well as the long and complicated recycling process severely limit their practical applications. Therefore, construction of novel MOFs composites with extremely high ease-of-use property has become a research hotspot, such as two-dimensional (2D) MOFs fibrous membranes. In this review, the exploitation of MOFs nanofibrous membranes via electrospinning and their applications in wastewater treatment are summarized. The MOFs nanofibers (NFs) architectures are established systematically by five routes: (1) direct electrospinning of MOFs-polymer; (2) induced growth of MOFs on electrospun NFs containing seeds; (3) growth of MOFs on electrospun organic NFs’ (4) growth of MOFs on electrospun inorganic NFs; and (5) simultaneous electrospinning and electrospraying. Furthermore, the applications of different types of MOFs nanofibrous membranes and their derivatives in water treatment and purification are discussed, including oil-water separation, the removal of heavy metal ions, organic dyes, personal care products, non-steroidal anti-inflammatory drugs (NSAIDs) and so on. The adsorption properties and mechanisms of electrospun MOFs nanofibrous membranes towards various environmental pollutants are discussed. Finally, the challenges of electrospun MOFs NFs, the limitations of their applications, and future development trends are prospected.     

Chitin and Chitosan Fibers

Chitin and chitosan are natural polymers extracted from various plants and animals. In recent years, these two polymers have attracted much interest because of their biodegradability, biocompatibility, wound-healing acceleration and many other unique properties. As a natural renewable resource, they offer many potential applications in a number of diversified fields. Chitin and chitosan fibers have been found useful as a biomaterial for potential applications such as sutures and wound dressings. This article presents a brief introduction to the properties of chitin and chitosan, and reviews the various attempts for the production of fibers from the two polymers. © 1997 John Wiley & Sons, Ltd.     

Comments on the Status and Future of Interfacial Polycondensation

Abstract

Interfacial polycondensation came into prominence in the 1950′s with the work of Schnell on polycarbonates, Conix on polyesters, and Wittbecker, Morgan and co-workers on polyurethanes, polyamides and other polymer classes. There were a few earlier patent references. The method has several variations and is a highly effective procedure for the rapid preparation of many polymers on a small scale. It is particularly appropriate for polymers which are thermally unstable or unmeltable, for use with volatile or unstable intermediates and for polymers with reactive functional groups. Literally thousands of polymers have been made by this process. There are a number of short-comings to the process, most of which can be overcome by adjustment of the polymerization conditions. Polycarbonates and aromatic polyamides are reported to be prepared commercially by stirred interfacial processes. Another application is the encapsulation of pesticides, inks, and other materials. As to the future, the processes are a basic part of the chemist's tool kit and will continue to be used in the laboratory for rapid syntheses and for those polymers which are not obtained as readily by other means. The basic tests of commercial use of these processes, as with any other process, will be attainment of results not available by other routes, economic considerations, and safety and environmental factors.     

Macromolecules containing bipyridine and terpyridine metal complexes: towards metallosupramolecular polymers

The ability of a broad range of N-heterocycles to act as very effective and stable complexation agents for several transition metal ions, such as cobalt(II), copper(II), nickel(II), and ruthenium(II), has long been known in analytical chemistry. This behavior was later utilized in supramolecular chemistry for the construction of highly sophisticated architectures, such as helicates, racks, and grids. The discovery of macromolecules by Staudinger in 1922 opened up avenues towards sophisticated materials with properties hitherto completely unknown. In the last few decades, the combination of macromolecular and supramolecular chemistry has been attempted by developing metal-complexing and metal-containing polymers for a wide variety of applications that range from filtration to catalysis. The stability of the polymer-metal complex is a fundamental requirement for such applications. In this respect, the use of bi- and terpyridines as chelating ligands is highly promising, since these molecules are known to form highly stable complexes with interesting physical properties with transition-metal ions. A large number of different structures have been designed for many different applications, but polymers based on the application of coordinative forces have been prepared in a few cases only. Furthermore, the synthetic procedures applied frequently resulted in low yields. During the last few years, strong efforts have been made in the direction of self-assembling and supramolecular polymers as novel materials with "intelligent" and tunable properties. In this review, an overview of this active area at the interface of supramolecular and macromolecular chemistry is given.     

Polymers and supercritical fluids: opportunities for vibrational spectroscopy

Supercritical fluids are used for enhanced processing of polymeric materials. Therefore, there is a need to understand how supercritical fluids interact with polymeric materials and how they may modify many facets of process operations. In situ spectroscopy provides a route for understanding and optimising polymer processing with supercritical fluids. In situ spectroscopy probes interactions between supercritical CO₂ and polymers at a molecular level and provides a fundamental understanding of the origin of the plasticising effect of supercritical carbon dioxide on glassy polymers. The changes in polymers subjected to supercritical fluids have been elucidated via in situ ATR(Attenuated Total Reflectance)-IR spectroscopy. The key feature of our new approach is the use of a modified diamond ATR accessory to measure spectra of polymers subjected to high-pressure gas, supercritical fluids or near-critical water. A variety of novel applications for the use of in situ ATR-IR spectroscopy to polymers are described.     

Electrospinning: a fascinating method for the preparation of ultrathin fibers

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.     

Thermal Degradation and Fire Behavior of High Performance Polymers

Abstract

High performance and high temperature polymers are a class of polymeric materials exhibiting high thermal stability and their resistance to fire makes them valuable assets for many applications. Those applications include as typical examples high temperature gas separation membranes, automotive and aerospace industry as well as the construction industry. The high performance polymers have been synthesized since the early 1960s, and have developed rapidly over the past few decades. Most high performance polymers comprise a highly aromatic backbone, linear chains, and strong inter-chain interactions. This review deals mostly with commercial polymeric materials. Studies regarding their thermal behavior, degradation mechanism and their reaction to fire have been synthetically combined in order to bring out potential insight concerning the effect of the thermal decomposition and thermal behavior on the fire properties of those polymers.     

Crystallization-driven self-assembly of semicrystalline block copolymers and end-functionalized polymers: A minireview

Self-assembly has been a powerful method to fabricate the polymer materials with well-defined structures and morphologies. Such assembled materials have shown wide potential applications in many fields such as nanomaterial, nanomedicine, lithography, and microelectronic. Crystallization has been a general behavior of stereoregular polymers. Besides the various noncovalent interactions, crystallization of polymer blocks or end groups can be an efficient way to manipulate the self-assembly pathway and assembled structures of polymers in both solid and solution. Crystallization-driven self-assembly has been widely implemented for the semicrystalline block copolymers (BCPs) and end-functionalized polymers. This minireview briefly presents the recent progresses in the crystallization-driven self-assembly of BCPs and end-functionalized polymers in both solid and solution states. Formation process, mechanism, and hierarchical structure of the crystallization-induced assemblies for BCPs and end-functionalized polymers are highlighted.     

Characterization of Engineering Polymers by Dynamic Mechanical Analysis

There is a growing need for the use of polymers in high-strength and engineering applications, and many new materials and composites have been developed to satisfy this need. Traditionally, thermosetting polymers have been employed as high-strength materials, with the incorporation of various fillers or additives to improve shortcomings in strength and temperature performance. Although these materials are largely unrivaled in high-temperature performance, some of the newer engineering thermoplastics, such as poly(ether ether ketone)(PEEK), poly(ether sulfone) (PES), poly(pheny1ene sulfide) (PPS), and the new backbone liquid-crystal polymers are becoming much more widely used. With this widespread use and with the increasing complexity of polymer blends and composites, there is a strong requirement for a universal means of characterizing such materials in terms of mechanical properties and high-temperature performance. A powerful and versatile analytical technique which is capable of application to a very wide range of materials is that of dynamic mechanical spectrometry. This technique can be used to establish basic material relaxation temperatures and frequencies, the modulus and loss behavior, as well as factors such as degree of cure, fder/matrix bonding, and phase separation.     

Coupling of waste water treatment with storage polymer production

Applied Biochemistry and Biotechnology - Storage polymers in bacterial cells can be extracted and used as biodegradable thermoplastics. However, widespread applications have been limited by high...     

Polymeric Scaffolds for Cartilage Tissue Engineering

Polymeric scaffolds are three-dimensional, porous structures that may be used as a vehicle to deliver cells or therapeutic factors to repair tissue defects. Both biodegradable and non-biodegradable polymers have been developed for this purpose. In this review, we survey the polymers that have been investigated for cartilage tissue engineering and discuss the critical parameters for successful applications in the future.     

Advanced Developments in Cyclic Polymers: Synthesis,Applications, and Perspectives

Due to the topological effect, cyclic polymers demonstrate different and unique physical and biological properties in comparison with linear counterparts having the same molecular-weight range. With advanced synthetic and analytic technologies, cyclic polymers with different topologies, e.g. multicyclic polymers, have been reported and well characterized. For example, various cyclic DNA and related structures, such as cyclic duplexes, have been prepared conveniently by click chemistry. These types of DNA have increased resistance to enzymatic degradation and have high thermodynamic stability, and thus, have potential therapeutic applications. In addition, cyclic polymers have also been used to prepare organic–inorganic hybrids for applications in catalysis, e.g. catalyst supports. Due to developments in synthetic technology, highly pure cyclic polymers could now be produced in large scale. Therefore, we anticipate discovering more applications in the near future. Despite their promise, cyclic polymers are still less explored than linear polymers like polyolefins and polycarbonates, which are widely used in daily life. Some critical issues, including controlling the molecular weight and finding suitable applications, remain big challenges in the cyclic-polymer field. This review briefly summarizes the commonly used synthetic methodologies and focuses more on the attractive functional materials and their biological properties and potential applications.     

The fire retardant behaviour of huntite and hydromagnesite - A review

Naturally occurring mixtures of hydromagnesite and huntite have found important industrial use. Their endothermic decomposition over a temperature range similar to that of commonly used polymers and their release of water and carbon dioxide, has led to such mixtures being successfully used as fire retardants. They have replaced aluminium hydroxide and magnesium hydroxide in many applications. The current understanding of the thermal decomposition mechanism of both minerals and their combination in natural mixtures has been reviewed and related to their fire retardant action. Both minerals contribute to the reduction in flammability of polymers although the extent of these interactions has not been fully investigated. However, the fire retardant mechanism of these minerals appears more complicated than either aluminium hydroxide or magnesium hydroxide.     

Characterization of internal structure of hydrated agar and gelatin matrices by cryo‐SEM

There has been a considerable interest in recent years in developing polymer gel matrices for many important applications such as 2DE for quantization and separation of a variety of proteins and drug delivery system to control the release of active agents. However, a well‐defined knowledge of the ultrastructures of the gels has been elusive. In this study, we report the characterization of two different polymers used in 2DE: Gelatin, a naturally occurring polymer derived from collagen (protein) and agar, a polymer of polysaccharide (sugar) origin. Low‐temperature SEM is used to examine the internal structure of these gels in their frozen natural hydrated states. Results of this study show that both polymers have an array of hollow cells that resembles honeycomb structures. While agar pores are almost circular, the corresponding Gaussian curve is very broad exhibiting a range of radii from nearly 370 to 700 nm. Gelatin pores are smaller and more homogeneous reflecting a narrower distribution from nearly 320 to 650 nm. Overall, these ultrastructural findings could be used to correlate with functions of the polymers.     

Zinc‐Catalyzed Depolymerization of End‐of‐Life Polysiloxanes

Polymers occupy an important role in our current society. Besides their great success, an issue is the accumulation of huge amounts of end‐of‐life polymers. Currently, the waste management is based primarily on landfills, thermal recycling, and downcycling. Notably, only a small portion of end‐of‐life materials is recycled by depolymerization, which refers to the creation of synthetic precursors that can be polymerized to new polymers to close the cycle. Widely used polymers in modern times are silicones (polysiloxanes), the intrinsic properties of which make their depolymerization demanding; only a few high‐temperature or less environmentally friendly processes have been reported. In this regard, we have established an efficient low‐temperature protocol for the depolymerization of silicones with benzoyl fluoride in the presence of cheap zinc salts as precatalysts to yield defined products. Notably, the products can be useful synthetic precursors for the preparation of new polymers, so that an overall recycling process is feasible.     

Recent Advances in Fullerene‐free Polymer Solar Cells: Materials and Devices

What is the most favorite and original chemistry developed in your research group? We focus on developing new organic photovoltaic materials and exploring their applications in photovoltaic devices. Based on the new materials, we can figure out the correlations among chemical strictures, optoelectronic properties, and photovoltaic behaviors. Our group originally demonstrated quite a few build blocks for making conjugated polymers for photovoltaic applications, some of them have been broadly used by the researchers in the field. How do you get into this specific field? Could you please share some experiences with our readers? I got into this field when I was a graduate student in 2002, just because my supervisor gave me a research topic for synthesis of new conjugated polymers. At that moment, as a fresh graduate student, I had no chance to say yes or no, but to do it. The field of organic solar cells is oriented by the new organic photovoltaic materials. In the past decades, the materials have been updated for a few generations, which promoted the device performance to be higher and closer to practical applications. We have to concentrate on the fundamental problems but also need to follow the pace of the filed. How do you supervise your students? In my opinion, the students need more specific projects to get into the field so as to be well trained at the beginning. In the later stage, I prefer to encourage them to find and creatively figure out the real fundamental problems. I used to give them a few questions: Why do you need to do this project? How to make a clear definition for the problem? Can you suggest a new and better approach to solve it? What is the most important personality for scientific research? Passion, perseverance and sense of innovation. What is your favorite journal(s)? The journals publishing the latest and/or systematic research works in chemistry and material science.