Suspension polymerization
Encyclopedia
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.
This process is used in the production of many commercial resins, including polyvinyl chloride (PVC)
, a widely used plastic, styrene resins including polystyrene
, expanded polystyrene, and high-impact polystyrene, as well as poly(styrene-acrylonitrile)
and poly(methyl methacrylate).
agent, enabling high rates of polymerization with little change in the temperature of the polymerizing solution. The reactions are usually done in a stirred tank reactor that mixes the solution using turbulent pressure or viscous shear forces. The stirring action helps to keep the monomer droplets separated and creates a more uniform suspension, which leads to a more narrow size distribution of the final polymer. The polymerization is usually carried to completion. The kinetics of the polymerization within an individual bead are similar to those of typical 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...
process that uses mechanical agitation to mix a 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...
or mixture of monomers in a liquid phase, such as water, while the monomers polymerize, forming spheres of polymer.
This process is used in the production of many commercial resins, including polyvinyl chloride (PVC)
PVC
Polyvinyl chloride is a plastic.PVC may also refer to:*Param Vir Chakra, India's highest military honor*Peripheral venous catheter, a small, flexible tube placed into a peripheral vein in order to administer medication or fluids...
, a widely used plastic, styrene resins including 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...
, expanded polystyrene, and high-impact polystyrene, as well as poly(styrene-acrylonitrile)
Styrene-acrylonitrile resin
Styrene acrylonitrile resin is a copolymer plastic consisting of styrene and acrylonitrile. It is also known as SAN. It is widely used in place of polystyrene owing to its greater thermal resistance...
and poly(methyl methacrylate).
Reaction Conditions
The reaction mixture consists of two phases, a liquid matrix and monomer drops. The monomer and initiator are insoluble in the liquid phase, so they form drops within the liquid matrix. A suspension agent is usually added to hinder monomer drops from coming together. The reaction mixture usually has a volume ratio of monomer to liquid phase of 0.1 to 0.5. The liquid phase acts as a heat transferHeat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
agent, enabling high rates of polymerization with little change in the temperature of the polymerizing solution. The reactions are usually done in a stirred tank reactor that mixes the solution using turbulent pressure or viscous shear forces. The stirring action helps to keep the monomer droplets separated and creates a more uniform suspension, which leads to a more narrow size distribution of the final polymer. The polymerization is usually carried to completion. The kinetics of the polymerization within an individual bead are similar to those of typical radical polymerization.
Particle Morphology
The polymer beads that result can range in size from 100 nm to 5 mm. The size is controlled by the stirring speed, the volume fraction of monomer, the concentration and identity of the stabilizers used, and the viscosities of the different components. Two main morphologies result. If the polymer is soluble in its monomer, the result is a smooth, translucent bead. This occurs for polymers such as [polystyrene] or [poly(methyl methacrylate)]. If the polymer is not soluble in its monomer, the resultant bead will be porus. This occurs for polymers such as [poly(vinyl chloride)] and [polyacrylonitrile]. The morphology of the polymer can be changed by adding a monomer [diluent], an inert liquid that is insoluble with the liquid matrix. The choice of monomer diluent and how soluble the monomer and polymer are in it gives a measure of control over the porosity of the resulting polymer.See also
- Radical PolymerizationRadical polymerizationFree 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...
- PolymerPolymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
- PolymerizationPolymerizationIn polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
- Step-Growth PolymerizationStep-growth polymerizationStep-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally occurring and some synthetic polymers are produced by step-growth...
- Superabsorbent PolymerSuperabsorbent polymerSuperabsorbent polymers are polymers that can absorb and retain extremely large amounts of a liquid relative to their own mass....