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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
A completely α-stereoregular 2,3,4-tri-O-benzyl-(l→6)-α-d-glucopyranan is prepared by ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-benzyl-β-d-glucopyranose according to Scheme I. A strong Lewis acid phosphorus pentafluoride (PF5) is the best catalyst for ring-opening polymerization. Walden inversion at the Cl carbon occurred, causing change of β-configuration of the monomer into α-configuration of the polymer. Debenzylation of the polymer is carried out with sodium in liquid ammonia, that is, by Birch reduction, to give OH-free (1→6)-α-d-glucopyranan: synthetic dextran.
Symmetrical Monomers Containing Other Multiple Bonds
Published in George B. Butler, Cyclopolymerization and Cyclocopolymerization, 2020
1,2,5,6-Diepoxyhexane was polymerized as early as 1964 under the influence of a variety of catalysts to afford soluble polymers for which tetrahydropyran recurring units were proposed. Aluminum isopropoxide, phosphorus pentafluoride-water, diethylzinc and triisobutyl aluminum were employed as catalysts. A diethylzinc-water catalyst system gave the highest molecular weight polymer with limited solubility {η = 0.45 dl/g] for 1,2,5,6-diepoxyhexane. The IR spectrum was consistent with a cyclic ether. An anionic mechanism for polymerization of 1,2,5,6-diepoxyhexane (5-22) was proposed.
Polysaccharides
Published in Stanislaw Penczek, H. R. Kricheldorf, A. Le Borgne, N. Spassky, T. Uryu, P. Klosinski, Models of Biopolymers by Ring-Opening Polymerization, 2018
Phosphorus pentafluoride was found to be the catalyst of choice. The benzyl group was used as the removable protective group. Combination of these two factors afforded successful synthesis of stereoregular polysaccharides. Although synthesis of a 1,6-α-linked polyglucose became possible in this way, the next problem was to achieve the high molecular weight because it is known that cationic polymerization rates of side reactions (i.e., transfer) are relatively large when compared with that of propagation.
Risk assessment of lithium-ion battery explosion: chemical leakages
Published in Journal of Toxicology and Environmental Health, Part B, 2018
Yoo Jung Park, Min Kook Kim, Hyung Sik Kim, Byung Mu Lee
The electrolyte of a lithium-ion battery is flammable and generally contains LiPF6 or other Li salts. When a high temperature is reached, the electrolyte evaporates and discharges from the battery cell, which may ignite immediately. The explosion emits a variety of toxic substances including CO (flue gas) (Li et al. 2018), hydrofluoric acid (HF), phosphorus pentafluoride (PF5), and phosphoryl fluoride (POF3), along with heat and fire. Lithium also reacts with the relative humidity of the air because of its good hydrophilicity. The OH ion supplied from the water in the reaction reacts with Li to produce lithium hydroxide (LiOH) (Larsson et al. 2017; Xu 2004) (Table 4).
Detailed characterization of particle emissions from battery fires
Published in Aerosol Science and Technology, 2022
Vinay Premnath, Yanyu Wang, Nolan Wright, Imad Khalek, Steven Uribe
Battery failure can be categorized into four failure stages. The first stage is when batteries are subjected to an abuse factor such as thermal (over-heating), electrical (over-charging) or mechanical (Lamb et al. 2015; Larsson and Mellander 2014; Ohsaki et al. 2005). Typically, electrolytes used in Li-ion batteries are composed of a Li salt such as lithium hexafluorophosphate (LiPF6) and a solvent. Commonly used solvents include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). These solvents are traditionally stable chemicals, however, the presence of lithium salt catalyzes their breakdown to volatile species in the presence of abuse factors that enhance thermal exposure (Larsson et al. 2017; Zinigrad et al. 2005). As electrical or thermal abuse continues, liquid electrolyte starts transforming to gas. Gases that include solvent vapors, carbon dioxide (CO2), carbon monoxide (CO), water vapor, hydroflouric acid (HF), lithium fluoride (LiF) among others eventually vent from the cell. This is referred to as Stage 2 of failure where the escaping gases may be susceptible to ignition. At this stage, early detection of leakage gases from electrolyte could help prevent thermal runaway if certain measures are implemented to stop abuse from continuing (Cai et al. 2020, 2021; Cai, Stefanopoulou, and Siegel 2019; Essl et al. 2021). If the battery cell continues to get subjected to the abuse factor, gas generation will continue to the point where pressure generated from these gases will eventually result in breaching the separator. This is classified as Stage 3 of failure and there is onset of smoke generation, and thermal runaway is imminent. The significant release of energy that follows separator breakdown results in a fire, and often, explosion (Stage 4). This results in the emissions of various species that include electrolyte solvent vapors, hydrogen, carbon monoxide (CO), volatile organic compounds (such as alkanes), water vapor, carbon dioxide, elemental carbon compounds, in addition to fluorine compounds stemming from electrolyte and electrode materials such as hydrogen fluoride, phosphorus pentafluoride, phosphoryl fluoride among others (Golubkov et al. 2014; Larsson et al. 2014; Larsson, Andersson, and Mellander 2016; Larsson and Mellander 2014; Nedjalkov et al. 2016). Other compounds are also released depending on the battery chemistry. While the above stages are more applicable for thermal and electrical abuse factors that lead to cell heating, mechanical abuse factors may directly result in failure stages 3 and 4 (Aiello et al. 2021; Doose, Haselrieder, and Kwade 2021; Essl, Golubkov, and Fuchs 2020; Feng et al. 2018; Huang et al. 2020; Yokoshima et al. 2019). After onset of thermal runaway, fire and gases could contribute toward heating adjacent cells thereby leading to propagation of thermal runaway (Larsson, Andersson, and Mellander 2016; Liu et al. 2016; Lopez, Jeevarajan, and Mukherjee 2015). Furthermore, these stages may also be influenced by the state-of-charge (SOC) of the cells (Golubkov et al. 2015).