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autoacceleration
Autoacceleration (Gel Effect, Trommsdorff-Norrish Effect) is a dangerous reaction behavior that can occur in free radical polymerization systems. It is due to the localized increases in viscosity of the polymerizing system that slow termination reactions. The removal of reaction obstacles therefore causes a rapid increase in the overall rate of reaction, leading to possible reaction runaway and altering the characteristics of the polymers produced.〔Alger, Mark. Polymer Science Dictionary. New York: Elsevier Applied Science, 1989. 28.〕
==Background==
Autoacceleration of the overall rate of a free radical polymerization system has been noted in many bulk polymerization systems. The polymerization of methyl methacrylate, for example, deviates strongly from classical mechanism behavior around 20 percent conversion; in this region the conversion and molecular weight of the polymer produced increases rapidly. This increase of polymerization is usually accompanied by a large rise in temperature if heat dissipation is not adequate. Without proper precautions, autoacceleration of polymerization systems could cause metallurgic failure of the reaction vessel or, worse, explosion.〔Chekal, Brian P. Understanding the Roles of Chemically-Controlled and Diffusion-Limited Processes in Determining the Severity of Autoacceleration Behavior in Free Radical Polymerization. Diss. Northwestern, 2002. 2002.〕
To avoid the occurrence of thermal runaway due to autoacceleration suspension polymerization techniques are employed to make polymers such as polystyrene. The droplets dispersed in the water are small reaction vessels, but the heat capacity of the water lowers the temperature rise, thus moderating the reaction.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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