Radical polymerization

Radical polymerization

Free radical polymerization is a method of polymerization by which a polymer forms by the successive addition of free radical building blocks. Free radicals can be formed via a number of different mechanisms usually involving separate initiator molecules...

 of pure styrene causes the viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 to increase. This retards the deactivation of the free radicals by radical-radical reactions, but it does not have such a great effect on the reaction of the radicals with styrene. Hence the concentration of free radicals increases and the rate of reaction increases, which can lead to thermal runaway

Thermal runaway

Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result...

. While the autoacceleration

Autoacceleration

Autoacceleration 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...

 seen with pure styrene is the classic example taught to chemistry

Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 undergraduates, this effect can occur during the polymerization

Polymerization

In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 of other monomer

Monomer

A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

s such as methyl methacrylate

Methyl methacrylate

Methyl methacrylate is an organic compound with the formula CH2=CCOOCH3. This colourless liquid, the methyl ester of methacrylic acid is a monomer produced on a large scale for the production of poly .-Production:...

.http://www.chem.rochester.edu/~chem421/autoac.htm

Avoiding thermal runaway is one of the reasons why suspension polymerization

Suspension polymerization

Suspension polymerization is a heterogeneous radical polymerization process that uses mechanical agitation to mix a monomer or mixture of monomers in a liquid phase, such as water, while the monomers polymerize, forming spheres of polymer....

 is such a popular way of making polystyrene

Polystyrene

Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...

. The droplets dispersed in the water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 are small reaction vessels, but the heat capacity

Heat capacity

Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...

 of the water lowers the temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

rise, thus moderating the reaction.