Editing Polymerization (section)

=== Photopolymerization ===
{{Main|Photopolymer}}
Most '''photopolymerization''' reactions are chain-growth polymerizations which are initiated by the absorption of visible<ref>{{cite journal |last1=McKenzie |first1=Thomas G. |last2=Fu |first2=Qiang |last3=Wong |first3=Edgar H. H. |last4=Dunstan |first4=Dave E. |last5=Qiao |first5=Greg G. |date=2015-06-23 |title=Visible Light Mediated Controlled Radical Polymerization in the Absence of Exogenous Radical Sources or Catalysts |journal=Macromolecules |volume=48 |issue=12 |pages=3864–3872 |doi=10.1021/acs.macromol.5b00965 |issn=0024-9297 |bibcode=2015MaMol..48.3864M |url=https://figshare.com/articles/journal_contribution/2155795/files/3789646.pdf}}</ref> or ultraviolet light. Photopolymerization can also be a step-growth polymerization.<ref>{{Cite journal |last=Kaya |first=Kerem |date=January 2023 |title=A green and fast method for PEDOT: Photoinduced step-growth polymerization of EDOT |url=https://linkinghub.elsevier.com/retrieve/pii/S1381514822003091 |journal=Reactive and Functional Polymers |language=en |volume=182 |pages=105464 |doi=10.1016/j.reactfunctpolym.2022.105464}}</ref> The light may be absorbed either directly by the reactant monomer (''direct'' photopolymerization), or else by a ''photosensitizer'' which absorbs the light and then transfers energy to the monomer. In general, only the initiation step differs from that of the ordinary thermal polymerization of the same monomer; subsequent propagation, termination, and chain-transfer steps are unchanged.<ref name=":0" />
In step-growth photopolymerization, absorption of light triggers an addition (or condensation) reaction between two comonomers that do not react without light. A propagation cycle is not initiated because each growth step requires the assistance of light.<ref name="Soto 2014">{{cite journal |last=Soto |first=Marc |author2=Sebastián, Rosa María |author3=Marquet, Jordi |year=2014 |title=Photochemical Activation of Extremely Weak Nucleophiles: Highly Fluorinated Urethanes and Polyurethanes from Polyfluoro Alcohols |journal=J. Org. Chem. |volume=79 |issue=11 |pages=5019–5027 |doi=10.1021/jo5005789 |pmid=24820955}}</ref>

Photopolymerization can be used as a photographic or printing process because polymerization only occurs in regions which have been exposed to light. Unreacted monomer can be removed from unexposed regions, leaving a relief polymeric image.<ref name=":0" /> Several forms of [[3D printing#Photopolymerization|3D printing]]—including layer-by-layer [[stereolithography]] and [[two-photon absorption#3D photopolymerization|two-photon absorption 3D photopolymerization]]—use photopolymerization.<ref>{{cite journal |title=Additive manufacturing of ceramics from preceramic polymers |journal=Additive Manufacturing |volume=27 |pages=80–90 |doi=10.1016/j.addma.2019.02.012 |date=May 2019 |arxiv=1905.02060 |last1=Wang |first1=Xifan |last2=Schmidt |first2=Franziska |last3=Hanaor |first3=Dorian |last4=Kamm |first4=Paul H. |last5=Li |first5=Shuang |last6=Gurlo |first6=Aleksander |s2cid=104470679}}</ref>

[[Multiphoton polymerization]] using single pulses have also been demonstrated for fabrication of complex structures using a [[digital micromirror device]].<ref>{{cite journal |last1=Mills |first1=Benjamin |last2=Grant-Jacob |first2=James A |last3=Feinaeugle |first3=Matthias |last4=Eason |first4=Robert W |date=2013-06-17 |title=Single-pulse multiphoton polymerization of complex structures using a digital multimirror device |journal=Optics Express |language=EN |volume=21 |issue=12 |pages=14853–8 |doi=10.1364/oe.21.014853 |pmid=23787672 |issn=1094-4087 |bibcode=2013OExpr..2114853M |url=https://eprints.soton.ac.uk/356463/1/oe-21-12-14853.pdf |doi-access=free}}</ref>