Bulk polymerization or mass polymerization is carried out by adding a soluble

radical initiator In chemistry, radical initiators are substances that can produce radical species under mild conditions and promote radical reactions. These substances generally possess weak bonds—bonds that have small bond dissociation energies. Radical i ...

to pure

monomer In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization. Classification Mo ...

in liquid state. The initiator should dissolve in the monomer. The reaction is initiated by heating or exposing to radiation. As the reaction proceeds the mixture becomes more viscous. The reaction is exothermic and a wide range of molecular masses are produced. Bulk polymerization is carried out in the absence of any solvent or dispersant and is thus the simplest in terms of formulation. It is used for most step-growth polymers and many types of chain-growth polymers. In the case of chain-growth reactions, which are generally exothermic, the heat evolved may cause the reaction to become too vigorous and difficult to control unless efficient cooling is used.

Advantages and disadvantages

Bulk

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

has several advantages over other methods, these advantages are:Abdullah Youssef, Abdal-Rhman. (2019). Solution & Bulk polymerization. 10.13140/RG.2.2.16472.96001/2. * The system is simple and requires thermal insulation. * The

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

obtained is pure. * Large castings may be prepared directly. *

Molecular weight distribution The molar mass distribution (or molecular weight distribution) describes the relationship between the number of moles of each polymer species (Ni) and the molar mass (Mi) of that species. In linear polymers, the individual polymer chains rarely have ...

can be easily changed * The product obtained has high optical clarity Disadvantages: * Heat transfer and mixing become difficult as the viscosity of reaction mass increases. * The problem of heat transfer is compounded by the highly exothermic nature of free radical addition polymerization. * The polymerization is obtained with a broad molecular weight distribution due to the high

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

and lack of good heat transfer. * very high molecular weights are obtained. * Gel effect. For reducing the disadvantages of bulk polymerization, the process can be carried out in a solution. This is known as

solution polymerization Solution polymerization is a method of industrial polymerization. In this procedure, a monomer is dissolved in a non-reactive solvent that contains a catalyst or initiator. The reaction results in a polymer which is also soluble in the chosen solv ...

Classification

There are two main types of bulk polymerization:

Quiescent bulk polymerization

There is no agitation in this type of bulk polymerization. This is often used to synthesize

cross-linked In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

and

thermosetting In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and ...

polymers. Due to dormant nature of the system, the Trommsdorff effect is significantly present, which in turn leads to longer chains and tougher material. The major disadvantages of this type of polymerization include entrapped bubbles (or voids) due to monomer boil-off and inability to convert all monomers.

Stirred bulk polymerization

Continuous stirring of the monomer happens in this type of polymerization. Very specific designs of reactors are used depending upon the

of the polymer. In some applications, the completed polymer melt is transferred from the reactor using a gear pump or applying moderate external pressure. It differs from the solution polymerization in a way that the monomer itself acts as a solvent.

References

{{Reflist Polymerization reactions fr:Procédé de polymérisation#Polymérisation en masse