Reagents for Polymerization

Find polymerization reagents for materials science polymer applications

Polymerization occurs when monomers react with each other to form long chains and can occur in various manners.

Addition polymerization occurs when the chain grows one unit at a time to incorporate monomers that usually have double or triple bonds. The double or triple bonds break and the electrons are then used to form new bonds. Addition polymerization occurs in three steps: initiation, propagation and termination. Chain growth starts very rapidly and continues steadily until termination. Conversely, condensation polymerization is generally a slower process that occurs between any two molecular units. Growth does not have to occur one unit at a time. Monomers for condensation polymerization usually have an alcohol, amine or carboxylic acid functionality. Bond formation results in the release of a small molecule (often water), hence, the term "condensation polymerization."

Initiators are often used to start the polymerization reaction. Free-radical initiation is the common initiation method. The free radicals necessary for this step can be generated either thermally (thermal initiators) or photochemically (photoinitiators).

During the polymerization process, additives can be used to adjust properties of the chemicals. Depending on the desired properties, plasticizers can be added to increase flexibility, dopants can be added for increased conductivity or cross-linking agents can be added to induce additional cross-chain bonds that ultimately increase polymer strength/rigidity.

Engineering polymers are a special class of desirable compounds that have achieved superior physical properties. These materials or material mixes have favorable mechanical properties such as stiffness, toughness or low creep. Polyamides, polyimides, polyesters and polysulfones fall into this category. These engineering polymers may incorporate fillers or additives to achieve the desired properties.