Array ( [0] => {{Short description|Chemical reaction to form polymer chains}} [1] => {{TopicTOC-Polymer}} [2] => {{Use American English|date=November 2020}} [3] => {{Use dmy dates|date=November 2020}} [4] => [5] => In [[polymer chemistry]], '''polymerization''' ([[American English]]), or '''polymerisation''' ([[British English]]), is a process of reacting [[monomer|monomer molecule]]s together in a [[chemical reaction]] to form [[polymer]] chains or three-dimensional networks.{{cite book |doi=10.1351/goldbook.P04740 |doi-access=free |chapter=Polymerization |title=The IUPAC Compendium of Chemical Terminology |year=2014}}{{Cite book |last=Young |first=Robert J. |url= |title=Introduction to polymers |publisher=Chapman and Hall |year=1981 |isbn=0-412-22170-5 |location=London |oclc=8086791}}{{Cite book |last1=Clayden |first1=Jonathan |url= |title=Organic chemistry |last2=Greeves |first2=Nick |last3=Warren |first3=Stuart |publisher=Oxford University Press |year=2001 |isbn=0-19-850347-4 |location=Oxford |pages=1450–1466 |oclc=43338068}} There are many forms of polymerization{{Cite book |last=Manas |first=Chanda |title=Introduction to Polymer Science and Chemistry:A Problem-Solving Approach |publisher=CRC Press |year=2023 |isbn=978-1-4665-5385-9 |edition=2nd |publication-date=2013}} and different systems exist to categorize them. [6] => [7] => [[File:IUPAC definition for polymerization.png|thumb|right|550px|link=https://doi.org/10.1351/goldbook.P04740|IUPAC definition for polymerization]] [8] => [9] => In [[chemical compound]]s, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to the [[functional group]]s present in the reactants and their inherent [[steric effects]]. In more straightforward polymerizations, [[alkenes]] form polymers through relatively simple [[free-radical reaction|radical reactions]]; in contrast, reactions involving substitution at a [[carbonyl group]] require more complex synthesis due to the way in which reactants polymerize. [10] => [11] => [[File:Polystyrene formation.PNG|thumb|right|400px|An example of '''alkene polymerization''', in which each [[styrene]] monomer's double bond reforms as a single bond plus a bond to another styrene monomer. The product is [[polystyrene]].]] [12] => [13] => As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such as [[polyethylene]] and [[polyvinyl chloride]] (PVC), which are produced in high tonnages each year due to their usefulness in manufacturing processes of commercial products, such as piping, insulation and packaging. In general, polymers such as PVC are referred to as "'''homopolymers'''", as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one monomer unit are referred to as [[copolymer]]s (or co-polymers).{{Cite book |last=Cowie |first=J. M. G. |url= |title=Polymers : chemistry and physics of modern materials |publisher=CRC Press |others=V. Arrighi |year=2008 |isbn=978-0-8493-9813-1 |edition=3rd |location=Boca Raton |pages=4 |oclc=82473191}} [14] => [15] => {| align="right" class="infobox" style="text-align:center;" [16] => [17] => | [18] => [19] =>
Homopolymers
[20] => [21] => :A + A + A+... \rightarrow AAAA ... [22] => [23] => [24] =>
Copolymers
[25] => [26] => :A + B + A+B... \rightarrow ABAB ... [27] => :A + B + A+B... \rightarrow AABB ... [28] => :A + B + A+B... \rightarrow BBAB ... [29] => |} [30] => [31] => Other monomer units, such as formaldehyde hydrates or simple aldehydes, are able to polymerize themselves at quite low temperatures (ca. −80 °C) to form [[trimer (chemistry)|trimer]]s; molecules consisting of 3 monomer units, which can [[cyclization|cyclize]] to form ring cyclic structures, or undergo further reactions to form [[tetramer]]s, or 4 monomer-unit compounds. Such small polymers are referred to as [[oligomer]]s. Generally, because formaldehyde is an exceptionally reactive electrophile it allows [[nucleophile|nucleophilic]] addition of [[hemiacetal]] intermediates, which are in general short-lived and relatively unstable "mid-stage" compounds that react with other non-polar molecules present to form more stable polymeric compounds. [32] => [33] => Polymerization that is not sufficiently moderated and proceeds at a fast rate can be very hazardous. This phenomenon is known as [[autoacceleration]], and can cause fires and explosions. [34] => [35] => ==Step-growth vs. chain-growth polymerization== [36] => Step-growth and chain-growth are the main classes of polymerization reaction mechanisms. The former is often easier to implement but requires precise control of stoichiometry. The latter more reliably affords high molecular-weight polymers, but only applies to certain monomers. [37] => [38] => [[File:Polymerization classification ENmod.png|thumb|A classification of the polymerization reactions|alt=|440x440px]] [39] => [40] => ===Step-growth=== [41] => {{Main|Step-growth polymerization}} [42] => [43] => In step-growth (or step) polymerization, pairs of reactants, of any lengths, combine at each step to form a longer polymer molecule. The [[Molar mass distribution#Number average molar mass|average molar mass]] increases slowly. Long chains form only late in the reaction.{{Cite book |last1=Allcock |first1=H. R. |url= |title=Contemporary polymer chemistry. |last2=Lampe |first2=Frederick Walter |last3=Mark |first3=James E. |publisher=Pearson/Prentice Hall |others=Frederick Walter Lampe, James E. Mark |year=2003 |isbn=0-13-065056-0 |edition=3rd |location=Upper Saddle River, N.J. |pages=29–30 |oclc=51096012}}{{Cite book |last=Fried |first=Joel R. |url= |title=Polymer science and technology |publisher=Prentice Hall Professional Technical Reference |year=2003 |isbn=0-13-018168-4 |edition=2nd |location=Upper Saddle River, NJ |pages=23 |oclc=51769096}} [44] => [45] => Step-growth polymers are formed by independent reaction steps between functional groups of monomer units, usually containing [[heteroatoms]] such as nitrogen or oxygen. Most step-growth polymers are also classified as [[condensation polymer]]s, since a small molecule such as water is lost when the polymer chain is lengthened. For example, [[polyester]] chains grow by reaction of [[Alcohol (chemistry)|alcohol]] and [[carboxylic acid]] groups to form [[ester]] links with loss of water. However, there are exceptions; for example [[polyurethane]]s are step-growth polymers formed from [[isocyanate]] and alcohol bifunctional monomers) without loss of water or other volatile molecules, and are classified as [[addition polymer]]s rather than condensation polymers. [46] => [47] => Step-growth polymers increase in molecular weight at a very slow rate at lower conversions and reach moderately high molecular weights only at very high conversion (i.e., >95%). '''Solid state polymerization''' to afford polyamides (e.g., nylons) is an example of step-growth polymerization.{{Ullmann |doi=10.1002/14356007.a21_487.pub3|title=Polyethylene|year=2014|last1=Jeremic|first1=Dusan|pages=1–42|isbn=9783527306732}} [48] => [49] => ===Chain-growth=== [50] => {{Main|Chain-growth polymerization}} [51] => In chain-growth (or chain) polymerization, the only chain-extension reaction step is the addition of a monomer to a growing chain with an active center such as a [[free radical]], [[cation]], or [[anion]]. Once the growth of a chain is initiated by formation of an active center, chain propagation is usually rapid by addition of a sequence of monomers. Long chains are formed from the beginning of the reaction. [52] => [53] => Chain-growth polymerization (or addition polymerization) involves the linking together of unsaturated monomers, especially containing carbon-carbon [[double bonds]]. The pi-bond is lost by formation of a new sigma bond. Chain-growth polymerization is involved in the manufacture of polymers such as [[polyethylene]], [[polypropylene]], [[polyvinyl chloride]] (PVC), and [[acrylate]]. In these cases, the alkenes RCH=CH2 are converted to high molecular weight alkanes (-RCHCH2-)n (R = H, CH3, Cl, CO2CH3). [54] => [55] => Other forms of chain growth polymerization include [[cationic addition polymerization]] and [[anionic addition polymerization]]. A special case of chain-growth polymerization leads to [[living polymerization]]. [[Ziegler–Natta polymerization]] allows considerable control of [[Branching (polymer chemistry)|polymer branching]]. [56] => [57] => [[File:Ethylene polymerization.png|thumb|right|Polymerization of [[ethylene]]]] [58] => [59] => Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is temperature control, also called [[heat management]], during these reactions, which are often highly exothermic. For example, for the polymerization of ethylene, 93.6 kJ of energy are released per mole of monomer. [60] => [61] => The manner in which polymerization is conducted is a highly evolved technology. Methods include [[emulsion polymerization]], [[solution polymerization]], [[suspension polymerization]], and [[precipitation polymerization]]. Although the polymer [[dispersity]] and molecular weight may be improved, these methods may introduce additional processing requirements to isolate the product from a solvent. [62] => [63] => === Photopolymerization === [64] => {{Main|Photopolymer}} [65] => Most '''photopolymerization''' reactions are chain-growth polymerizations which are initiated by the absorption of visible{{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}} or ultraviolet light. Photopolymerization can also be a step-growth polymerization.{{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}} 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. [66] => 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.{{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}} [67] => [68] => 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. 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.{{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}} [69] => [70] => Multiphoton polymerization using single pulses have also been demonstrated for fabrication of complex structures using a [[digital micromirror device]].{{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}} [71] => [72] => ==See also== [73] => {{Div col|colwidth=22em}} [74] => * [[Cross-link]] [75] => * [[In situ polymerization|''In situ'' polymerization]] [76] => * [[Metallocene]] [77] => * [[Plasma polymerization]] [78] => * [[Polymer characterization]] [79] => * [[Polymer physics]] [80] => * [[Reversible addition−fragmentation chain-transfer polymerization]] [81] => * [[Ring-opening polymerization]] [82] => * [[Sequence-controlled polymer]]s [83] => * [[Sol-gel]] [84] => {{Div col end}} [85] => [86] => ==References== [87] => {{Reflist}} [88] => [89] => {{Authority control}} [90] => [[Category:Polymerization reactions| ]] [] => )
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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 forms of polymerization and different systems exist to categorize them.

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