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Thermal initiation involves initiating a reaction in the presence of heat, usually at very high temperatures. Heating a reaction can result in radical initiation of the substrate(s). [ 6 ] In the presence of heat, a monomer can self-initiate and react with other monomers or pairs of monomers.
As a result, in the case of chemical or thermal initiation, it is reasonable to assume that it is the N-chloroammonium ion which affords the ammonium free radical. The situation changes, however, when the reaction is initiated upon irradiation with UV light.
Initiation is the first step of the polymerization process. During initiation, an active center is created from which a polymer chain is generated. Not all monomers are susceptible to all types of initiators. Radical initiation works best on the carbon–carbon double bond of vinyl monomers and the carbon–oxygen double bond in aldehydes and ...
Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is temperature control, also called heat management, during these reactions, which are often highly exothermic. For example, for the polymerization of ethylene, 93.6 kJ of energy are released per mole of ...
High energy initiation refers to the generation of chain carriers by radiation. Chemical initiation is due to a chemical initiator. For the case of radical polymerization as an example, chain initiation involves the dissociation of a radical initiator molecule (I) which is easily dissociated by heat or light into two free radicals (2 R°).
For chain-growth polymerization, the overall activation energy is = +, where i, p and t refer respectively to initiation, propagation and termination steps. The propagation step normally has a very small activation energy, so that the overall value is negative if the activation energy for termination is larger than that for initiation.
Even though all these steps can appear in one chain reaction, the minimum necessary ones are Initiation, propagation, and termination. An example of a simple chain reaction is the thermal decomposition of acetaldehyde (CH 3 CHO) to methane (CH 4) and carbon monoxide (CO).
Inorganic peroxides function analogously to organic peroxides. Many polymers are often produced from the alkenes upon initiation with peroxydisulfate salts. In solution, peroxydisulfate dissociates to give sulfate radicals: [3] [O 3 SO-OSO 3] 2− ⇌ 2 [SO 4] −. The sulfate radical adds to an alkene forming radical sulfate esters, e.g. .