View source for Polyethylenimine

{{Not to be confused with|Polyetherimide|text=[[Polyetherimide]] (also known as PEI)}}{{Chembox
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| ImageFile = Polyethylenimin.svg
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| IUPACName = Poly(iminoethylene)
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| OtherNames = Polyaziridine, Poly[imino(1,2-ethanediyl)] 
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| CASNo = 9002-98-6 
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|Section2={{Chembox Properties
| Formula = (C<sub>2</sub>H<sub>5</sub>N)<sub>n</sub>, linear form
| MolarMass = 43.04 ([[repeat unit]]), mass of polymer variable
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'''Polyethylenimine''' ('''PEI''') or '''polyaziridine''' is a [[polymer]] with repeating units composed of the [[amine]] group and two [[carbon]] [[Aliphatic_compound|aliphatic]]  ''CH{{sub|2}}CH{{sub|2}}'' spacers. Linear polyethyleneimines contain all [[Amines#Classification_of_amines|secondary amines]], in contrast to branched PEIs which contain primary, secondary and tertiary amino groups. Totally branched, [[dendrimer]]ic forms were also reported.<ref>
{{cite journal
| last1= Yemul 
| first1= Omprakash 
| last2= Imae 
| first2= Toyoko 
| year= 2008 
| title= Synthesis and characterization of poly(ethyleneimine) dendrimers 
| journal= Colloid & Polymer Science 
| volume= 286 
| issue= 6–7
| pages=747–752 
| doi= 10.1007/s00396-007-1830-6 
| s2cid= 98538201 
}}</ref> PEI is produced on an industrial scale and finds many applications usually derived from its [[polyelectrolyte|polycationic]] character.<ref>
{{cite book 
| last1= Davidson 
| first1= Robert L. 
| last2= Sittig 
| first2= Marshall 
| title= Water-soluble resins 
| year=1968 
| publisher=Reinhold Book Corp. 
| isbn= 978-0278916135 
}}</ref>

{{multiple image
| align = right
| direction = vertical
| width = 230
| image1 = Linear PEI.png
| caption1 = Linear PEI fragment
| image2 = Branched PEI.png
| caption2 = Typical branched PEI fragment
| image3 = G4 dendrimer PEI.png
| caption3 = PEI dendrimer generation 4
| background color = #FFFFFF
}}

==Properties==

The linear PEI is a semi-crystalline solid at [[room temperature]] while branched PEI is  a fully amorphous polymer existing as a liquid at all molecular weights. Linear polyethyleneimine is soluble in hot water, at low pH, in [[methanol]], [[ethanol]], or [[chloroform]].  It is insoluble in cold water, [[benzene]], [[Diethyl ether|ethyl ether]], and [[acetone]]. Linear polyethylenimine has a [[melting point]] of around 67&nbsp;°C.<ref name=":0">{{Cite journal |last1=Soradech |first1=Sitthiphong |last2=Williams |first2=Adrian C. |last3=Khutoryanskiy |first3=Vitaliy V. |date=2022-10-24 |title=Physically Cross-Linked Cryogels of Linear Polyethyleneimine: Influence of Cooling Temperature and Solvent Composition |journal=Macromolecules |volume=55 |issue=21 |language=en |pages=9537–9546 |doi=10.1021/acs.macromol.2c01308 |bibcode=2022MaMol..55.9537S |s2cid=253149614 |issn=0024-9297|doi-access=free }}</ref> Both linear and branched polyethylneimine can be stored at room temperature. Linear polyethylenimine is able to form [[Aerogel#Freeze-Drying|cryogels]] upon freezing and subsequent thawing of its aqueous solutions.<ref name=":0" />

==Synthesis==

Branched PEI can be synthesized by the [[ring opening polymerization]] of [[aziridine]].<ref>Zhuk, D. S., Gembitskii, P. A., and Kargin V. A. Russian Chemical Reviews; Vol 34:7.1965</ref> Depending on the reaction conditions different degree of branching can be achieved. Linear PEI is available by post-modification of other polymers like poly(2-oxazolines) <ref>
{{cite journal 
| last1= Tanaka 
| first1= Ryuichi 
| last2= Ueoka 
| first2= Isao 
| last3= Takaki 
| first3= Yasuhiro 
| last4= Kataoka 
| first4= Kazuya 
| last5= Saito 
| first5= Shogo 
| year= 1983 
| title= High molecular weight linear polyethylenimine and poly(N-methylethylenimine) 
| journal= Macromolecules 
| volume= 16 
| issue= 6
| pages=849–853 
| doi= 10.1021/ma00240a003 
| bibcode= 1983MaMol..16..849T 
}}</ref> or ''N''-substituted polyaziridines.<ref>
{{cite journal |last1= Weyts |first1= Katrien F. |last2= Goethals |first2= Eric J. |year= 1988 |title= New synthesis of linear polyethyleneimine 
| journal= Polymer Bulletin 
| volume= 19 
| issue= 1 
| pages=13–19 
| doi= 10.1007/bf00255018 
|s2cid= 97101501 }}</ref> Linear PEI was synthesised by the hydrolysis of poly(2-ethyl-2-oxazoline)<ref>{{cite journal | last1 = Brissault | first1 = B. | display-authors = etal   | year = 2003 | title = Synthesis of Linear Polyethylenimine Derivatives for DNA Transfection | journal = Bioconjugate Chemistry | volume = 14 | issue = 3| pages = 581–587 | doi=10.1021/bc0200529| pmid = 12757382 }}</ref> and sold as jetPEI.<ref>{{cite web |url=http://www.polyplus-transfection.com/transfection-reagents/high-throughput-screening-jetpei/ |title=High Throughput Screening « Polyplus Transfection |access-date=2010-04-02 |url-status=dead |archive-url=https://web.archive.org/web/20100302173423/http://www.polyplus-transfection.com/transfection-reagents/high-throughput-screening-jetpei/ |archive-date=2010-03-02 }}</ref> The current generation in-vivo-jetPEI uses bespoke poly(2-ethyl-2-oxazoline) polymers as precursors.<ref>{{Cite web | url=http://www.wipo.int/pctdb/en/wo.jsp?WO=2009016507&IA=IB2008002339&DISPLAY=DOCS | archive-url=https://archive.today/20120805235646/http://www.wipo.int/pctdb/en/wo.jsp?WO=2009016507&IA=IB2008002339&DISPLAY=DOCS | url-status=dead | archive-date=2012-08-05 | title=Method for Manufacturing Linear Polyethylenimine (pei) for Transfection Purpose and Linear Pei Obtained with Such Method }}</ref>

==Applications==

Polyethyleneimine finds many applications in products like: detergents, adhesives, water treatment agents and cosmetics.<ref name=Ullmann>{{Ullmann|doi=10.1002/14356007.a03_239.pub2|title=Aziridines|year=2006|last1=Steuerle|first1=Ulrich|last2=Feuerhake|first2=Robert|isbn=3527306730}}</ref> Owing to its ability to modify the surface of cellulose fibres, PEI is employed as a wet-strength agent in the [[Papermaking|paper-making process]].<ref>
{{cite journal
 |last1     = Wågberg
 |first1    = Lars
 |year      = 2000
 |title     = Polyelectrolyte adsorption onto cellulose fibres – a review
 |journal   = Nordic Pulp & Paper Research Journal
 |volume    = 15
 |issue     = 5
 |pages     = 586–597
 |doi       = 10.3183/NPPRJ-2000-15-05-p586-597
 |s2cid = 4942367
 |url       = https://www.researchgate.net/publication/242230437
}}</ref> It is also used as flocculating agent with silica sols and as a chelating agent with the ability to complex metal ions such as zinc and zirconium.<ref>
{{cite book 
| last1= Madkour 
| first1= Tarek M. 
| title= Polymer Data Handbook 
| year=1999 
| publisher= Oxford University Press, Inc. 
| isbn= 978-0195107890 
| page= 490
}}</ref> There are also other highly specialized PEI applications:

===Biology===
PEI has a number of uses in laboratory biology, especially [[tissue culture]], but is also toxic to cells if used in excess.<ref name="Vancha 2004">{{cite journal|year=2004|title=Use of polyethyleneimine polymer in cell culture as attachment factor and lipofection enhancer|journal=BMC Biotechnology|volume=4|pages=23|doi=10.1186/1472-6750-4-23|pmc=526208|pmid=15485583|author=Vancha AR|display-authors=etal |doi-access=free }}</ref><ref>{{cite journal|year=2006|title=Molecular hurdles in polyfectin design and mechanistic background to polycation induced cytotoxicity|journal=Advanced Drug Delivery Reviews|volume=58|issue=14|pages=1523–1531|doi=10.1016/j.addr.2006.09.008|pmid=17079050|last1=Hunter|first1=A. C.}}</ref> Toxicity is by two different mechanisms,<ref>{{cite journal|year=2005|title=A two-stage poly(ethylenimine)-mediated cytotoxicity: implications for gene transfer/therapy|journal=Molecular Therapy|volume=11|issue=6|pages=990–995|doi=10.1016/j.ymthe.2005.02.010|pmid=15922971|last1=Moghimi|first1=S. M.|display-authors=etal|doi-access=free}}</ref> the disruption of the cell membrane leading to necrotic cell death (immediate) and disruption of the mitochondrial membrane after internalisation leading to apoptosis (delayed).

====Attachment promoter====

Polyethyleneimines are used in the cell culture of weakly anchoring cells to increase attachment. PEI is a cationic polymer; the negatively charged outer surfaces of cells are attracted to dishes coated in PEI, facilitating stronger attachments between the cells and the plate.

====Transfection reagent====

Poly(ethylenimine) was the second polymeric transfection agent discovered,<ref>{{cite journal | last1 = Boussif | first1 = O. | display-authors = etal   | year = 1995 | title = A Versatile Vector for Gene and Oligonucleotide Transfer into Cells in Culture and in vivo: Polyethylenimine | journal = Proceedings of the National Academy of Sciences | volume = 92 | issue = 16| pages = 7297–7301 | doi = 10.1073/pnas.92.16.7297 | pmid = 7638184 | bibcode = 1995PNAS...92.7297B| pmc = 41326| doi-access = free }}</ref> after poly-L-lysine. PEI condenses DNA into positively charged particles, which bind to anionic cell surface residues and are brought into the cell via [[endocytosis]]. Once inside the cell, protonation of the amines results in an influx of counter-ions and a lowering of the osmotic potential. Osmotic swelling results and bursts the vesicle releasing the polymer-DNA complex (polyplex) into the cytoplasm. If the polyplex unpacks then the DNA is free to diffuse to the nucleus.<ref name="Rudolf 2000">{{cite journal |year= 2000| title= In vivo gene delivery to the lung using polyethylenimine and fractured polyamidoamine dendrimers| journal= Journal of Gene Medicine | volume= 2| pages= 269–78 | pmid= 10953918 |last1= Rudolph |first1= C |last2= Lausier |first2= J |last3= Naundorf |first3= S |last4= Müller |first4= RH |last5= Rosenecker |first5= J |issue= 4 |doi= 10.1002/1521-2254(200007/08)2:4<269::AID-JGM112>3.0.CO;2-F | s2cid= 31273799}}</ref><ref name="Aknic 2004">{{cite journal |year= 2004| title= Exploring polyethylenimine-mediated DNA transfection and the proton sponge hypothesis | journal= Journal of Gene Medicine | volume= 7| pages= 657–663 | doi=10.1002/jgm.696 |pmid= 15543529 |last1= Akinc |first1= A |last2= Thomas |first2= M |last3= Klibanov |first3= AM |last4= Langer |first4= R |issue= 5 | s2cid= 25740208 }}</ref>

====Permeabilization of gram negative bacteria====
Poly(ethylenimine) is also an effective permeabilizer of the outer membrane of [[Gram-negative bacteria]].<ref name="Helander Alakomi Latva-Kala Koski pp. 3193–3199">{{cite journal | last1=Helander | first1=I. M. | last2=Alakomi | first2=H.-L. | last3=Latva-Kala | first3=K. | last4=Koski | first4=P. | title=Polyethyleneimine is an effective permeabilizer of Gram-negative bacteria | journal=Microbiology | publisher=Microbiology Society | volume=143 | issue=10 | date=1997-10-01 | issn=1350-0872 | doi=10.1099/00221287-143-10-3193 | pages=3193–3199| pmid=9353921 | doi-access=free }}</ref>

===CO<sub>2</sub> capture===

Both linear and branched polyethylenimine have been used for CO<sub>2</sub> capture, frequently impregnated over porous materials. First use of PEI polymer in CO<sub>2</sub> capture was devoted to improve the CO<sub>2</sub> removal in space craft applications, impregnated over a polymeric matrix.<ref>{{cite journal | last1 = Satyapal | first1 = S. | last2 = Filburn | first2 = T. | last3 = Trela | first3 = J. | last4 = Strange | first4 = J. | year = 2001 | title = Performance and Properties of a Solid Amine Sorbent for Carbon Dioxide Removal in Space Life Support Applications| journal = Energy & Fuels | volume = 15 | issue = 2| pages = 250–255 | doi=10.1021/ef0002391}}</ref> After that, the support was changed to MCM-41, an hexagonal mesostructured silica, and large amounts of PEI were retained in the so-called "molecular basket".<ref>{{cite journal | last1 = Xu | first1 = X. | last2 = Song | first2 = C. | last3 = Andrésen | first3 = J. M. | last4 = Miller | first4 = B. G. | last5 = Scaroni | first5 = A. W. | year = 2002 | title = Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2Capture| journal = Energy & Fuels | volume = 16 | issue = 6| pages = 1463–1469 | doi=10.1021/ef020058u}}</ref> MCM-41-PEI adsorbent materials led to higher CO<sub>2</sub> adsorption capacities than bulk PEI or MCM-41 material individually considered. The authors claim that, in this case, a synergic effect takes place due to the high PEI dispersion inside the pore structure of the material. As a result of this improvement, further works were developed to study more in depth the behaviour of these materials. Exhaustive works have been focused on the CO<sub>2</sub> adsorption capacity as well as the CO<sub>2</sub>/O<sub>2</sub> and CO<sub>2</sub>/N<sub>2</sub> adsorption selectivity of several MCM-41-PEI materials with PEI polymers.<ref>X. Xu, C. Song, R. Wincek J. M. Andrésen, B. G. Miller, A. W. Scaroni, ''Fuel Chem. Div. Prepr.'' 2003; 48 162-163</ref><ref>X. Xu, C. Song, B. G. Miller, A. W. Scaroni, ''Ind. Eng. Chem. Res.'' 2005; 44  8113-8119</ref> Also, PEI impregnation has been tested over different supports such as a glass fiber matrix <ref>{{cite journal | last1 = Li | first1 = P. | last2 = Ge | first2 = B. | last3 = Zhang | first3 = S. | last4 = Chen | first4 = S. | last5 = Zhang | first5 = Q. | last6 = Zhao | first6 = Y. | year = 2008 | title = CO2Capture by Polyethylenimine-Modified Fibrous Adsorbent| journal = Langmuir | volume = 24 | issue = 13| pages = 6567–6574 | doi=10.1021/la800791s| pmid = 18507414 }}</ref> and monoliths.<ref>C. Chen, S. T. Yang, W. S. Ahn, R. Ryoo,  "Title" ''Chem. Commun.'' (2009) 3627-3629</ref> However, for an appropriate performance under real conditions in post-combustion capture (mild temperatures between 45-75&nbsp;°C and the presence of moisture) it is necessary to use thermally and hydrothermally stable silica materials, such as [[Santa Barbara Amorphous-15|SBA-15]],<ref>{{cite journal | last1 = Sanz | first1 = R. | last2 = Calleja | first2 = G. | last3 = Arencibia | first3 = A. | last4 = Sanz-Pérez | first4 = E. S. | year = 2010 | journal = Appl. Surf. Sci. | volume = 256 | issue = 17| pages = 5323–5328 |title=CO2 adsorption on branched polyethyleneimine-impregnated mesoporous silica SBA-15 | doi=10.1016/j.apsusc.2009.12.070| bibcode = 2010ApSS..256.5323S }}</ref> which also presents an hexagonal mesostructure. Moisture and real world conditions have also been tested when using PEI-impregnated materials to adsorb CO<sub>2</sub> from the air.<ref>{{cite journal | title=Carbon Dioxide Capture from the Air Using a Polyamine Based Regenerable Solid Adsorbent|last1 = Goeppert | first1 = A. | last2 = Czaun | first2 = M. | last3 = May | first3 = R. B. | last4 = Prakash | first4 = G. K. Surya | last5 = Olah | first5 = G. A. | last6 = Narayanan | first6 = S. R. | year = 2011 | journal = Journal of the American Chemical Society | volume = 133 | issue = 50|pages = 20164–7 | doi=10.1021/ja2100005|pmid = 22103291 }}</ref>

A detailed comparison among PEI and other amino-containing molecules showed an excellent performance of PEI-containing samples with cycles. Also, only a slight decrease was registered in their CO<sub>2</sub> uptake when increasing the temperature from 25 to 100&nbsp;°C, demonstrating a high contribution of chemisorption to the adsorption capacity of these solids. For the same reason, the adsorption capacity under diluted CO<sub>2</sub> was up to 90% of the value under pure CO<sub>2</sub> and also, a high unwanted selectivity towards SO<sub>2</sub> was observed.<ref>{{cite journal | last1 = Sanz-Pérez | first1 = E.S. | last2 = Olivares-Marín | first2 = M. | last3 = Arencibia | first3 = A. | last4 = Sanz | first4 = R. | last5 = Calleja | title=CO2 adsorption performance of amino-functionalized SBA-15 under post-combustion conditions|first5 = G. | last6 = Maroto-Valer | first6 = M.M. | year = 2013 | journal = Int. J. Greenh. Gas Control | volume = 17 | page = 366 | doi=10.1016/j.ijggc.2013.05.011| hdl = 10115/11746 | hdl-access = free }}</ref> Lately, many efforts have been made in order to improve PEI diffusion within the porous structure of the support used. A better dispersion of PEI and a higher CO<sub>2</sub> efficiency (CO<sub>2</sub>/NH molar ratio) were achieved by impregnating a template-occluded PE-MCM-41 material rather than perfect cylindrical pores of a calcined material,<ref>{{cite journal | last1 = Heydari-Gorji | first1 = A. | last2 = Belmabkhout | first2 = Y. | last3 = Sayari | first3 = A. | year = 2011 | title = Polyethylenimine-Impregnated Mesoporous Silica: Effect of Amine Loading and Surface Alkyl Chains on CO2Adsorption| journal = Langmuir | volume = 27 | issue = 20| pages = 12411–6 | doi=10.1021/la202972t| pmid = 21902260 }}</ref> following a previously described route.<ref>{{cite journal | last1 = Yue | first1 = M.B. | last2 = Sun | first2 = L.B. | last3 = Cao | first3 = Y. | last4 = Wang | first4 = Y. | last5 = Wang | first5 = Z.J. | last6 = Zhu | first6 = J.H. | year = 2008 | title = Efficient CO2 Capturer Derived from As-Synthesized MCM-41 Modified with Amine| journal = Chem. Eur. J. | volume = 14 | issue = 11| pages = 3442–51 | doi=10.1002/chem.200701467| pmid = 18283702 }}</ref> The combined use of organosilanes such as aminopropyl-trimethoxysilane, AP, and PEI has also been studied. The first approach used a combination of them to impregnate porous supports, achieving faster CO<sub>2</sub>-adsorption kinetics and higher stability during reutilization cycles, but no higher efficiencies.<ref>{{cite journal | last1 = Choi | first1 = S. | last2 = Gray | first2 = M. L. | last3 = Jones | first3 = C.W. | year = 2011 | title = Amine-tethered solid absorbents coupling high adsorption capacity and regenerability for CO2 capture from ambient air | journal = ChemSusChem | volume = 4 | issue = 5| pages = 628–35 | doi = 10.1002/cssc.201000355 | pmid = 21548105 | bibcode = 2011ChSCh...4..628C }}</ref> A novel method is the so-called "double-functionalization". It is based on the impregnation of materials previously functionalized by grafting (covalent bonding of organosilanes). Amino groups incorporated by both paths have shown synergic effects, achieving high CO<sub>2</sub> uptakes up to 235&nbsp;mg CO<sub>2</sub>/g (5.34&nbsp;mmol CO<sub>2</sub>/g).<ref>{{cite journal | last1 = Sanz | first1 = R. | last2 = Calleja |title=Development of high efficiency adsorbents for CO2 capture based on a double-functionalization method of grafting and impregnation| first2 = G. | last3 = Arencibia | first3 = A. | last4 = Sanz-Pérez | first4 = E.S. | year = 2013 | journal = J. Mater. Chem. A | volume = 1 | issue = 6| page = 1956 | doi = 10.1039/c2ta01343f }}</ref> CO<sub>2</sub> adsorption kinetics were also studied for these materials, showing similar adsorption rates as impregnated solids.<ref>{{cite journal | last1 = Sanz | first1 = R. | last2 = Calleja |title=CO2 Uptake and Adsorption Kinetics of Pore-Expanded SBA-15 Double-Functionalized with Amino Groups| first2 = G. | last3 = Arencibia | first3 = A. | last4 = Sanz-Pérez | first4 = E.S. | year = 2013 | journal = Energy & Fuels | volume = 27 | issue = 12| page = 7637 | doi=10.1021/ef4015229}}</ref> This is an interesting finding, taking into account the smaller pore volume available in double-functionalized materials. Thus, it can be also concluded that their higher CO<sub>2</sub> uptake and efficiency compared to impregnated solids can be ascribed to a synergic effect of the amino groups incorporated by two methods (grafting and impregnation) rather than to a faster adsorption kinetics.

===Low work function modifier for electronics===

''Poly(ethylenimine) and poly(ethylenimine) ethoxylated'' (PEIE) have been shown as effective low-work function modifiers for organic electronics by Zhou and Kippelen et al.<ref>{{cite journal |doi=10.1126/science.1218829|title=A Universal Method to Produce Low-Work Function Electrodes for Organic Electronics|year=2012|last1=Zhou|first1=Y.|last2=Fuentes-Hernandez|first2=C.|last3=Shim|first3=J.|last4=Meyer|first4=J.|last5=Giordano|first5=A. J.|last6=Li|first6=H.|last7=Winget|first7=P.|last8=Papadopoulos|first8=T.|last9=Cheun|first9=H.|last10=Kim|first10=J.|last11=Fenoll|first11=M.|last12=Dindar|first12=A.|last13=Haske|first13=W.|last14=Najafabadi|first14=E.|last15=Khan|first15=T. M.|last16=Sojoudi|first16=H.|last17=Barlow|first17=S.|last18=Graham|first18=S.|last19=Bredas|first19=J.-L.|last20=Marder|first20=S. R.|last21=Kahn|first21=A.|last22=Kippelen|first22=B.|journal=Science|volume=336|issue=6079|pages=327–332|pmid=22517855|bibcode=2012Sci...336..327Z|s2cid=9949593}}</ref> It could universally reduce the work function of metals, metal oxides, conducting polymers and graphene, and so on. It is very important that low-work function solution-processed conducting polymer could be produced by the PEI or PEIE modification. Based on this discovery, the polymers have been widely used for organic solar cells, organic light-emitting diodes, organic field-effect transistors, perovskite solar cells, perovskite light-emitting diodes, quantum-dot solar cells and light-emitting diodes etc.

=== Use in delivery of HIV-gene therapies ===
Polyethylenimine (PEI), a cationic polymer, has been widely studied and shown great promise as an efficient gene delivery vehicle. Likewise, the HIV-1 Tat peptide, a cell-permeable peptide, has been successfully used for intracellular gene delivery.<ref>{{Cite journal|last1=Yamano|first1=Seiichi|last2=Dai|first2=Jisen|last3=Hanatani|first3=Shigeru|last4=Haku|first4=Ken|last5=Yamanaka|first5=Takuto|last6=Ishioka|first6=Mika|last7=Takayama|first7=Tadahiro|last8=Yuvienco|first8=Carlo|last9=Khapli|first9=Sachin|last10=Moursi|first10=Amr M.|last11=Montclare|first11=Jin K.|date=2014-02-01|title=Long-term efficient gene delivery using polyethylenimine with modified Tat peptide|url=https://www.sciencedirect.com/science/article/pii/S0142961213013501|journal=Biomaterials|language=en|volume=35|issue=5|pages=1705–1715|doi=10.1016/j.biomaterials.2013.11.012|pmid=24268201 |issn=0142-9612}}</ref>

==See also==
* [[Tetraethylenepentamine]]
* [[Ethylenediamine]]
* [[Polyetherimide]] (Also goes by PEI)
* [[Polyimine]]

==References==
{{reflist|30em}}

[[Category:Polyelectrolytes]]
[[Category:Polymers]]
[[Category:Amines]]