In polymer chemistry, autoacceleration (gel 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.[1] It is also known as the Trommsdorff–Norrish effect after German chemist Johann Trommsdorff and British chemist Ronald G.W. Norrish.