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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).
Biodegradable Polymers
Published in Ram K. Gupta, Conducting Polymers, 2022
Eman Abdallah Ismail, Mbuso Faya, Edith Amuhaya, Calvin A. Omolo, Thirumala Govender
Addition polymerization is also defined as chain-growth polymerization. Unlike condensation polymerization, addition polymerization reactions do not involve the loss of a small molecule. The monomers that usually undergo addition polymerization are those that are unsaturated, such as aldehydes, olefins, and acetylenes. This reaction proceeds in a stepwise fashion by forming reactive intermediates. This polymerization is usually exothermic because it involves the conversion of a p bond in the monomer into a sigma bond in the polymer. Polymers that are synthesized through this process are characterized by high molecular weights. While this process is mainly used to prepare straight-chain polymers, cross-linking can be achieved by using monomers containing two double bonds [22]. There are three possible mechanisms through which polymers can be prepared: anionic polymerization, cationic polymerization, and radical polymerization. The exact mechanism will depend on the reaction conditions used as well as the presence of electron-withdrawing or electron-donating groups on the monomers.
Molecular Description of Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
Polymerization is a process leading to the synthesis of large molecules (polymers or macromolecules) as a result of the binding of molecular building blocks called monomers. Molecules obtained by binding only a relatively small number of monomer units are usually denoted as oligomers. Particularly for heterophase polymerization, one must consider the fact that the properties of oligomers greatly differ from that of polymers. Important differences exist with respect to their physical properties (aggregation state, mobility, solubility, association, and swelling behavior) and all mechanical properties. In addition, the shorter the chain length, the stronger the influence of the end groups on these properties. The bonds between monomer units can be chemical (e.g., covalent bonds) or physical (e.g., hydrogen bonding, metal coordination). When monomer units are physically bonded, the resulting macromolecules are denoted as supramolecularpolymers [41, 42].
Recent advances in the synthesis of and sensing applications for metal-organic framework-molecularly imprinted polymer (MOF-MIP) composites
Published in Critical Reviews in Environmental Science and Technology, 2023
Yongbiao Hua, Deepak Kukkar, Richard J. C. Brown, Ki-Hyun Kim
Generally, the target analyte itself is used as the template when synthesizing MOF-MIPs. However, templates that are toxic, expensive, dangerous (e.g., virus), or chemically labile (e.g., proteins) under the necessary polymerization conditions (e.g., heating) could hinder the development and application of MOF-MIPs. Therefore, dummy template technology (using a structural analogue of the target compound as a template) should be developed. In addition, optimizing polymerization systems (i.e., template, functional monomer, solvent, and cross-linker) is laborious, environmentally unfriendly, and expensive. Therefore, the computational approach (e.g., DFT) is a useful first step in designing MOF-MIPs with high efficiency and environmental-friendliness. Computational modeling could improve understanding of the interactions between the monomer and template, thereby providing better guidance for constructing MOF-MIPs. Accordingly, more efforts should be made to develop theoretical approaches for optimizing MOF-MIPs with good selectivity and low LODs for target analyte sensing. In addition, efforts have been made to assess the potential of the covalent organic framework (COF) as an alternative of MOF for the construction of MIP-based sensors. However, the limited number and complicated fabrication process of COFs may restrict their application for the MIP-based sensors relative to MOFs. The application of MOF-MIPs is expected to offer intriguing possibilities for analyzing various compounds at ultra-trace concentrations in complex sample matrices.
3-Dimensional membrane capsules: Synthesis modulations for the remediation of environmental pollutants – A critical review
Published in Critical Reviews in Environmental Science and Technology, 2022
Imran Ali, Juying Li, Changsheng Peng, Muhammad Qasim, Zahid M. Khan, Iffat Naz, Muhammad Sultan, Muhammad Rauf, Waheed Iqbal, Hafiz Muhammad Adeel Sharif
Polymerization can be described as a method of reacting monomers in a chemical reaction to develop polymer chains or 3-D networks. There have been varieties of reaction mechanisms that vary in their convolution due to different functionalities in the reactants and their fundamental steric properties (Hadizade et al., 2017; X. Huang et al., 2019; K. Zhang et al., 2014). Various researchers have employed this route to synthesize 3-D MCs for environmental remediation, as details have been discussed in Table 1, and their pictorial demonstration has been provided in the supplementary information (Figure S6). For instance, chelate resin (SPADNS incorporated into Ceralite IR-400 beads) was encapsulated into polystyrene through interfacial polymerization with W/O/W emulsions for the preparation of polystyrene microcapsules to adsorb and recover Cd2+ from mixed metal solutions (Singh & Srivastava, 2005). Moreover, various uncommon or nonconventional techniques have also been employed for the fabrication of different kinds of 3-D MCs (Table 1). Figure S7 shows a pictorial illustration of these synthetic methods. Further, Table 2 depicts the pros and cons of the synthetic techniques. Overall, the titration gel/sol-gel and chemical crosslinking techniques are assumed to be green, environmentally friendly, economical and practically suitable for the remediation of environmental pollutants, although other techniques also have their own advantages and disadvantages (Table 2).
Evolution in the surface modification of textiles: a review
Published in Textile Progress, 2018
Ayoub Nadi, Aicha Boukhriss, Aziz Bentis, Ezzoubeir Jabrane, Said Gmouh
Homopolymerization generally denotes the formation of a linear polymer formed from a monomer or an oligomer, and may be accomplished in many ways, including addition polymerization, step-growth polymerization and ring-opening polymerization. Addition polymerization describes the method where monomers are added one-by-one to an active site on the growing chain. In step-growth polymerization, the molecular weight of the polymer chain builds up slowly and there is only one reaction mechanism for the formation of polymer; ring-opening polymerization is a reaction in which the rings of cyclic monomers are opened, allowing them to be joined together linearly. The polymer types used for affixing these homopolymers to the fibre are diverse, namely polyurethane, polydimethylsiloxane and polyacrylic acid [40].