Editing Living polymerization (section)

{{Short description|Chain-growth polymerization without the ability to terminate}}
{{Use dmy dates|date=February 2020}}
In [[polymer chemistry]], '''living polymerization''' is a form of [[chain growth polymerization]] where the ability of a growing [[polymer chain]] to [[chain termination|terminate]] has been removed.<ref>{{Cite journal | doi = 10.5254/1.3535823| title = Recent Advances in Anionic Polymerization| journal = Rubber Chemistry and Technology| volume = 54| issue = 3| pages = 627–640| year = 1981| last1 = Halasa | first1 = A. F. }}</ref><ref>Moad, Graeme and Solomon, David H. (2006) ''The Chemistry of Radical Polymerization''. 2nd ed. Elsevier. {{ISBN|0-08-044286-2}}</ref> This can be accomplished in a variety of ways. [[Chain termination]] and [[chain transfer reaction]]s are absent and the rate of [[chain initiation]] is also much larger than the rate of [[chain propagation]]. The result is that the polymer chains grow at a more constant [[reaction rate|rate]] than seen in traditional chain [[polymerization]] and their lengths remain very similar (i.e. they have a very low [[polydispersity index]]).  Living polymerization is a popular method for synthesizing [[block copolymer]]s since the polymer can be synthesized in stages, each stage containing a different [[monomer]]. Additional advantages are predetermined [[molar mass]] and control over [[end-group]]s.

{{Quote box
| title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition
| quote = '''Living polymerization''':  A chain polymerization from which chain transfer and chain termination are absent.

''Note'': In many cases, the rate of chain initiation is fast compared with the rate of chain propagation, so that the number of kinetic-chain carriers is essentially constant throughout the polymerization.<ref>{{cite journal|title=Glossary of basic terms in polymer science (IUPAC Recommendations 1996)|journal=[[Pure and Applied Chemistry]]|year=1996|volume=68|issue=12|pages=2287–2311|doi=10.1351/pac199668122287|url=http://pac.iupac.org/publications/pac/pdf/1996/pdf/6812x2287.html|last1=Jenkins|first1=A. D.|last2=Kratochvíl|first2=P.|last3=Stepto|first3=R. F. T.|last4=Suter|first4=U. W.|doi-access=free}}</ref>
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Living polymerization is desirable because it offers precision and control in macromolecular synthesis.  This is important since many of the novel/useful properties of polymers result from their microstructure and molecular weight.   Since [[molecular weight]] and [[dispersity]] are less controlled in non-living polymerizations, this method is more desirable for materials design<ref name=Cowie /><ref name=Principles />

In many cases, living polymerization reactions are confused or thought to be synonymous with controlled polymerizations.  While these polymerization reactions are very similar, there is a distinction between the definitions of these two reactions.  While living polymerizations are defined as polymerization reactions where termination or chain transfer is eliminated, controlled polymerization reactions are reactions where termination is suppressed, but not eliminated, through the introduction of a dormant state of the polymer.<ref name=Cowie /><ref name=Principles /> However, this distinction is still up for debate in the literature.

The main living polymerization techniques are:
* [[Living anionic polymerization]]
* [[Living cationic polymerization]]
* Living [[ring-opening metathesis polymerization]]
* [[Living free radical polymerization]]
* Living chain-growth polycondensations