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Emergence, Chemical Nature, Classification, Environmental Impact, and Analytical Challenges of Various Plastics
Published in Hyunjung Kim, Microplastics, 2023
It is quite challenging to produce an adequate definition of the word “plastics,” all plastics materials, before compounding with additives, consist of a mass of very large molecules (macromolecules), which, in turn, are composed of many repeating small pieces molecules called monomers. The chemical reaction in which macromolecules are formed from monomers is known as polymerization. There are two main types of polymerization, namely chain reaction polymerization and step reaction polymerization, often referred to by their older names, addition, and condensation polymerization (Billmeyer, 1984; Young and Lovell, 2011).
Polyhexahydrotriazines: Synthesis and Thermal Studies
Published in Didier Rouxel, Sabu Thomas, Nandakumar Kalarikkal, Sajith T. Abdulrahman, Advanced Polymeric Materials, 2022
Nitish Paul Tharakan, J. Dhanalakshmi, C. T. Vijayakumar
A polymer is a large molecule or macromolecule, composed of many repeated subunits. Because of their broad range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as deoxyribonucleic acid and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals [1].
Green Hydrogen Energy: Storage in Carbon Nanomaterials and Polymers
Published in Neha Kanwar Rawat, Tatiana G. Volova, A. K. Haghi, Applied Biopolymer Technology and Bioplastics, 2021
Brahmananda Chakraborty, Gopal Sanyal
A polymer is a substance having a molecular structure composed of essentially from a huge number of collectively bonded similar units [161]. Polymerization is the process by which macromolecules are formed by linking together monomer molecules through chemical reactions [162]. For their organic nature, the polymeric frameworks consist of light elements providing a burden-advantage in many purposes. The long-chain nature sets polymers apart from other materials and gives rise to their characteristic properties. Depending on the nature of the skeletal structure they possess, polymers can be classified as linear, branched, and network or cross-linked polymers [163]. It is the skeletal structure’s variation which is responsible for major difference in their properties. A higher crosslink density imparts superior rigidity to a polymer.
Fabrication of polymer-based self-assembly nanocarriers loaded with a crizotinib and gemcitabine: potential therapeutics for the treatment of endometrial cancer
Published in Journal of Biomaterials Science, Polymer Edition, 2022
Jiaolin Yang, Hongrui Guo, Jing Lei, Sanyuan Zhang, Shaoguo Zhang, Jirong Bai, Sufen Li
According to the features of a nanoparticle delivery structure mentioned earlier, the investigation into the use of diverse materials, as a nanocarrier precursor, is a critical necessity to enhance the adaptability and results obtained by such systems [19–21]. Polymers are macromolecules that comprise a linear or a branching chain, produced by the covalent union of one or many kinds of the unit known as monomers. These monomers may have any structure if they contain two functional groups, at least when they can react with another monomer [22]. Ideally, a polymer might be produced to achieve specific characteristics by selecting the correct type of monomer. Polymers include a particular sort of substance and allow the researchers to adapt them according to needs or ultimate purposes due to their highly synthetic versatility [22–25]. Polymeric tailoring may be carried out on biopolymers directly by chemical derivation to achieve characteristics. The fabrication of polymeric materials from their monomers is another approach, resulting in a wide variety of structures and uses. Therefore, nanotechnology generally takes on more importance polymeric materials and is employed for drug delivery systems as a promising nanoparticle [22–28].
Revisiting the Early History of Synthetic Polymers: Critiques and New Insights
Published in Ambix, 2018
Macromolecular polymers and plastics comprise a ubiquitous chemical technology in modern society, and their production represents a significant aspect of chemical industry today.1 The modern view of polymers as macromolecular chains of covalently-linked repeating units (“many parts,” the literal sense of the Greek-derived word “poly-mer”) was introduced by the German chemist Hermann Staudinger (1881–1965) in the 1920s,2 an event that constituted a major development in our understanding of molecular structure. However, the chemical study of these materials long predates the macromolecular concept. Natural polymers were chemically modified in an empirical fashion at an early date, followed in the nineteenth century by the production of completely synthetic substances that we now understand to be polymers, including polyaniline, polystyrene, cuprene, poly(vinyl chloride), polyisobutylene, and polyisoprene (these are of course their common contemporary names; the chemical structures of some of these substances are shown in Figure 1).3
Ground-state calculations of confined hydrogen molecule H2 using variational Monte Carlo method
Published in Molecular Physics, 2018
S. B. Doma, F. N. El-Gammal, A. A. Amer
Now, we introduce a simple chemical analysis concerning the catalytic role of enzymes [39, 40]. Enzymes are macromolecular biological catalysts which play a central role in life due to their catalytic properties. The molecules at the beginning of the process are called substrates and the enzyme converts these into different molecules, called products. The active site is always a non-rigid polar cavity, or crevice, where the substrate will be rearranged into products. Considering a confined molecule with the energy given in point A, there are two cases for converting from the confined state to the free state. In the first case, let us assume a sudden release of the constraint; this will relax the bonding electron into the free state with similar internuclear distance R. In this hypothesis, the vertical transition of the electrons from A → B (or from confined to unconfined state) leads to a change in the free molecule state and leaves it in a vibrational excited state. In the second case, if the switch-off of the constraint is slower, the relaxation pathway becomes A → C. In this relaxation pathway, the nuclei have time to move and so they gain kinetic energy.