Photopolymerization

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Photopolymerizations (also photoinitiated polymerization ) are polymerizations by the absorption initiated by visible or ultraviolet light, typically by a photoinitiator . Depending on the type of initiator and its decomposition reaction, radical or ionic chain polymerizations can be initiated. As a rule, the only difference between photopolymerization and conventional chain polymerization is the initiation step; the following steps, such as chain growth and chain termination, are identical. Photosensitizers are often used for photopolymerization . They absorb the light and transfer the energy absorbed to the actual initiator of the polymerization, whereby the sensitizer is not consumed in the reaction. Compounds such as acetophenone , benzophenone and thioxanthone are used as photosensitizers .

Photopolymerizations of synthetic resins , such as, for example, unsaturated polyester resins or vinyl ester resins , which are mixtures of prepolymers and monomers, lead to crosslinking , with thermosets being formed. The prepolymers of the two examples carry two vinyl groups or several C =C double bonds, which lead to crosslinking in independent chain growth reactions. Cross-links are also possible if the main chains of the prepolymers carry chromophores that form free radicals with photoinitiation and thus initiate polymerization. Photopolymerizations are usually carried out as bulk polymerizations.

Applications

Photopolymerizations are used to harden special printing inks , tooth fillings , coatings of glass fibers and discs and photoresists (photoresist).

If synthetic resins are applied to carrier materials and exposed to targeted exposure, polymerisation only takes place in regions that were exposed to light. The remaining regions can then be removed. This is used in photolithography in semiconductor technology. This principle can be extended three-dimensionally so that photopolymerization is used in 3D printing .

See also

Individual evidence

  1. ↑ Entry on photoinduced polymerization . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.P04618 Version: 2.3.3.
  2. ↑ Ulrich Jonas, Patrick Theato: IUPAC Recommendations: Glossary of terms related to kinetics, thermodynamics and mechanisms of polymerizations , Angew. Chem. , 2009, 121, p. 9734.
  3. ^ Entry on photosensitization . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.P04652 Version: 2.3.3.
  4. ↑ a b Jürgen Falbe, Manfred Regitz (Ed.): CD Römpp Chemie Lexikon , Thieme, Stuttgart, 1995.