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Copolymers, Microstructure, and Stereoregularity
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
Stereoregularity is obtained by coordination polymerization in the presence of particular catalysts. The most commonly used systems for the polymerization of α-olefins are referred to as Ziegler–Natta catalysts, a class which actually spans a large variety of particular compounds. The mechanisms of action of these catalysts are typically rather complicated. More recently there have been rapid advances in the development of single-site catalysts, which are usually based on metallocenes: a metal center coordinated to one or more cyclopentadienyl ligands. The terminology refers to the presence of a well-defined catalytic site throughout the polymerization medium, leading to more homogeneous products. These systems are capable of being fine-tuned to regulate a variety of structural features, including stereochemistry and comonomer addition.
Monomers, Polymers, and Plastics
Published in James G. Speight, Handbook of Petrochemical Processes, 2019
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of α-olefins (alpha-olefins, 1-alkenes). Two general classes of Ziegler–Natta catalysts are employed and are distinguished by their solubility: (i) heterogeneous supported catalysts such as those based on titanium compounds which are used in polymerization reactions in combination with co-catalysts—organo-aluminum compounds such as triethylaluminum (Al(C2H5)3) and (ii) homogeneous catalysts usually based on complexes of titanium, zirconium, hafnium which are usually used in combination with a different organo-aluminum co-catalyst, methyl aluminoxane (or methylalumoxane)—these catalysts traditionally contain not only metallocene derivatives but also feature multidentate oxygen- and nitrogen-based ligands.
Chain-Growth Polymerization
Published in Anil Kumar, Rakesh K. Gupta, Fundamentals of Polymer Engineering, 2018
The most important characteristic of the Ziegler–Natta catalyst system is its ability to stereoregulate the polymer. The configuration of the resultant polymer depends on the choice of the catalyst system and its crystalline structure. Stereoregulation is believed to occur as follows:
Degradation of polypropylene-poly-L-lactide blends by Bacillus isolates: a microcosm and field evaluation
Published in Bioremediation Journal, 2022
Kimi Jain, H. Bhunia, M. Sudhakara Reddy
Plastics are an essential and intrinsic part of human life and are used in various applications including packaging, agriculture, textiles, disposable items, and many more. Polyethylene (PE) and polypropylene (PP) are commonly used plastics, which are bioinert in nature because of their high molecular mass, hydrophobicity, and lack of functional groups. This causes accumulation of these materials in the environment and their disposal becomes a major concern across the globe (Arutchelvi et al. 2008). More than 140 million tonnes of plastics are produced worldwide every year (Shimao 2001) and about 79% of it ends up as waste in landfills or in the environment and pollute land and waterbodies including oceans and seas. Polypropylene, a thermoplastic polymer produced from propylene units using Ziegler–Natta catalyst is light in weight, resistant to chemicals, acids, solvents and possesses flexibility and is the second most utilized polymer after PE (Krueger, Harms, and Schlosser 2015). The global demand of PP expected to reach 87.35 million tons by 2022 (Plastemart.com 2016).
Chlorine in waste-derived solid recovered fuel (SRF), co-combusted in cement kilns: A systematic review of sources, reactions, fate and implications
Published in Critical Reviews in Environmental Science and Technology, 2021
Spyridoula Gerassimidou, Costas A. Velis, Paul T. Williams, Marco J. Castaldi, Leon Black, Dimitrios Komilis
Inorganic Cl, consisting of alkali metal chlorides such as NaCl, KCl, CaCl2 (Table 3), is prevalent in the ‘food waste’ fraction. The high proportion of ‘food waste’ in MSW makes NaCl the major contributor to the [Cl] load in MSW (Guo et al., 2001; Ma et al., 2010; Wu, Wang, Chai, Takahashi, & Shimaoka, 2016). But, inorganic Cl is not entirely present only in ‘food waste’. Ziegler-Natta catalysts used in the polymerization of polyolefin are composed of TiCl3 and MgCl2 leading to the presence of Cl in polyofelin plastic (Shamiri et al., 2014). Additionally, packaging components, such as plastic bottles of chlorinated detergents, may often contain remnants of chloride compounds such as sodium hypochlorite - the most common chloride used for bleaching (Zoller, 2008).
Levoglucosenone-derived synthesis of bio-based solvents and polyesters
Published in Green Chemistry Letters and Reviews, 2023
Cicely M. Warne, Sami Fadlallah, Adrian C. Whitwood, James Sherwood, Louis M. M. Mouterde, Florent Allais, Georg M. Guebitz, Con R. McElroy, Alessandro Pellis
Important in the field of polymer synthesis is principle 9 of Green Chemistry, which aims to use catalysts whenever possible (13). Catalysts are commonly used in polymer synthesis, with Ziegler–Natta catalysts being the most popularly employed for polyolefin production (14). For polyester synthesis, biocatalysts are particularly attractive from a sustainable perspective; they are derived from renewable resources and often require mild reaction conditions (15). Another is principle 5 of Green Chemistry, the use of safer solvents and auxiliaries. Solvents represent a significant portion of the environmental impact of a reaction, and ionic liquids, supercritical fluids and bio based solvents have all been tested in polymer synthesis (14).