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Polymeric Biomaterials
Published in Joyce Y. Wong, Joseph D. Bronzino, Biomaterials, 2007
Hai Bang Lee, Gilson Khang, Jin Ho Lee
The breaking of a double bond can be made with an initiator. This is usually a free radical such as benzoyl peroxide (H5C6COO–OOCC6H5). The initiation can be activated by heat, ultraviolet light, and other chemicals. The free radicals (initiators) can react with monomers and this free radical can react with another monomer and the process can continue on. This process is called propagation. The propagation process can be terminated by combining two free radicals, by transfer, or by disproportionate processes. Some of the free radical polymers are given in Table 3.3. There are three more types of initiating species for addition polymerization beside free-radicals; cations, anions, and coordination (stereospecific) catalysts. Some monomers can use two or more of the initiation processes but others can use only one process as given in Table 3.3.
Acrylic Adhesives
Published in István Benedek, Mikhail M. Feldstein, Technology of Pressure-Sensitive Adhesives and Products, 2008
Initiation is achieved in one of two ways: by homolytic dissociation, using heat or UV light, or by a redox reaction. Two well-known examples of thermal initiators used in solution polymerization are illustrated in Figure 5.20 (for thermal and redox initiators used in emulsion polymerization see Section 5.4.3.2.1). Note that the primary radical must further react with a monomer to begin the polymerization process. A significant fraction of primary radicals are often lost to formation of by-products.
Investigation of Aviation Lubricant Aging under Engine Representative Conditions
Published in Tribology Transactions, 2021
Abdolkarim Sheikhansari, Ehsan Alborzi, Christopher Parks, Spiridon Siouris, Simon Blakey
The proposed mechanism for lubricant thermal degradation through autoxidation is shown in Table 4. The main criterion for the initiation step is based on the low value of activation energy and the order of kinetics. In this regard, reactions between the substrate and molecular oxygen are less probable to be considered as the main initiation step. Therefore, thermal decomposition of hydroperoxides through homolytic fission is proposed to be a possible reaction step for the initiation stage as follows. This reaction can be accelerated by the complex of metals in the lubricant (36–39).
A coupled model of composite synthesis in combustion regime
Published in Combustion Theory and Modelling, 2022
Anna Georgievna Knyazeva, Natalia Valerievna Bukrina
Currently, there are numerous methods for synthesising composites [1–3 and other]. One of the effective methods for composite production is based on combustion synthesis, SHS [4–6]. The method involves the use of the internal energy of initial reagents. After local initiation of the reaction in a thin layer of initial reagents, the reaction front spontaneously propagates along the whole system due to heat transfer from hot products to initial components. This heat initiates and sustains the reaction.