View source for Polypropylene glycol

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| Name           = Polypropylene glycol
| OtherNames      = Propylene oxide homopolymer<BR />Poly (propene oxide) <BR />
| ImageFile      = Polypropylenglycol.svg
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'''Polypropylene glycol''' or '''polypropylene oxide''' is the [[polymer]] (or macromolecule) of [[propylene glycol]].<ref>{{Cite web |work = PubChem |title=2-(2-Hydroxypropoxy)propan-1-ol |url=https://pubchem.ncbi.nlm.nih.gov/compound/32881 |access-date=2022-11-14 |publisher = U.S. National Library of Medicine |language=en}}</ref> Chemically it is a [[polyether]], and, more generally speaking, it's a polyalkylene glycol (PAG) H S Code 3907.2000. The term polypropylene glycol or '''PPG''' is reserved for polymer of low- to medium-range [[molar mass]] when the nature of the [[end-group]], which is usually a [[hydroxyl]] group, still matters. The term "oxide" is used for high-molar-mass polymer when end-groups no longer affect polymer properties. Between 60 and 70% of propylene oxide is converted to [[Polyol#Polyols in polymer chemistry|polyether polyols]] by the process called [[alkoxylation]].<ref>{{Ullmann|vauthors =  Adam N, Avar G, Blankenheim H, Friederichs W, Giersig M, Weigand E, Halfmann M, Wittbecker FW, Larimer DR, Maier U, Meyer-Ahrens S, Noble KL, Wussow HG | display-authors = 6 |date=2005 |title=Polyurethanes |doi=10.1002/14356007.a21_665.pub2}}</ref>

== Polymerization ==
Polypropylene glycol is produced by [[ring-opening polymerization]] of [[propylene oxide]]. The [[Radical initiator|initiator]] is an [[Alcohol (chemistry)|alcohol]] and the [[catalyst]] a [[base (chemistry)|base]], usually [[potassium hydroxide]]. When the initiator is [[ethylene glycol]] or [[water]] the polymer is linear. With a multifunctional initiator like [[glycerine]], [[pentaerythritol]] or [[sorbitol]] the polymer branches out.

[[File:Polypropyleneglycol.svg|300px|center|Polypropylene glycol]]

Conventional [[polymerization]] of propylene oxide results in an [[atactic]] polymer. The [[isotactic]] polymer can be produced from [[optically active]] propylene oxide, but at a high cost.  A [[salen ligand|salen]] [[cobalt]] [[catalyst]] was reported in 2005 to provide isotactic polymerization of the [[prochiral]] propylene oxide<ref name="pmid16104709">{{cite journal | vauthors = Peretti KL, Ajiro H, Cohen CT, Lobkovsky EB, Coates GW | title = A highly active, isospecific cobalt catalyst for propylene oxide polymerization | journal = Journal of the American Chemical Society | volume = 127 | issue = 33 | pages = 11566–7 | date = August 2005 | pmid = 16104709 | doi = 10.1021/ja053451y }}</ref>

[[File:Polypropylene oxide catalyst.svg|thumb|Cobalt catalyst for isotactic polypropylene oxide]]

== Properties ==
PPG has many properties in common with [[polyethylene glycol]]. The polymer is a liquid at room temperature. [[Solubility]] in water decreases rapidly with increasing [[molar mass]]. Secondary hydroxyl groups in PPG are less reactive than primary hydroxyl groups in polyethylene glycol. PPG is less toxic than PEG, so biotechnologicals are now mainly produced with PPG.<ref>{{cite journal | vauthors = Thurman EM, Ferrer I, Rosenblum J, Linden K, Ryan JN | title = Identification of polypropylene glycols and polyethylene glycol carboxylates in flowback and produced water from hydraulic fracturing | journal = Journal of Hazardous Materials | volume = 323 | issue = Pt A | pages = 11–17 | date = February 2017 | pmid = 26947804 | doi = 10.1016/j.jhazmat.2016.02.041 | series = Special Issue on Emerging Contaminants in engineered and natural environment | doi-access =free  }}</ref><ref>{{cite journal | vauthors = Wang R, Hughes T, Beck S, Vakil S, Li S, Pantano P, Draper RK | title = Generation of toxic degradation products by sonication of Pluronic® dispersants: implications for nanotoxicity testing | journal = Nanotoxicology | volume = 7 | issue = 7 | pages = 1272–1281 | date = November 2013 | pmid = 23030523 | pmc = 3657567 | doi = 10.3109/17435390.2012.736547 }}</ref><ref>{{Cite journal | vauthors = Thangavelu SA, Mukherjee M, Layana K, Kumar CD, Sulthana YR, Kumar RR, Ananthan A, Muthulakshmi V, Mandal AB | display-authors = 6 |date=2020-06-15 |title=Biodegradable polyurethanes foam and foam fullerenes nanocomposite strips by one-shot moulding: Physicochemical and mechanical properties |journal=Materials Science in Semiconductor Processing |language=en |volume=112 |pages=105018 |doi=10.1016/j.mssp.2020.105018 |s2cid=213206957 |issn=1369-8001}}</ref>

[[File:PPG4000vsPPG400WaterSolubility.jpg|thumb|Difference in water solubility of PPG4000 and PPG400]]

== Uses ==
PPG is used in many [[polyurethane]] formulations.<ref>{{Cite journal | vauthors = Chattopadhyay DK, Raju NP, Vairamani M, Raju KV |date=2008-04-01 |title=Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI) based polyurethane prepolymer by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-mass spectrometry |journal=Progress in Organic Coatings |language=en |volume=62 |issue=2 |pages=117–122 |doi=10.1016/j.porgcoat.2007.09.021 |issn=0300-9440}}</ref><ref>{{Cite journal | vauthors = Xu Z, Cui Y, Li T, Dang H, Li J, Cheng F |date=July 2020 |title=Enhanced Mechanical and Shape Memory Properties of Poly(propylene glycol)‐Based Star‐Shaped Polyurethane |journal= Macromolecular Chemistry and Physics |language=en |volume=221 |issue=13 |pages=2000082 |doi= 10.1002/macp.202000082 |s2cid=225563251 |issn=1022-1352}}</ref> Synthesis of waterborne polymers has been a feature with this substance.<ref>{{Cite patent | inventor = Kim KJ, Hu R, Grove JL | assign1 = Arkema Inc | country = US | title = Water soluble polymers and polymer adducts along with aqueous solutions thereof Patent | number = 10920011 | gdate = 16 February 2021 }}</ref> As the basic building block is [[propylene oxide]], there are 3 carbons per oxygen on the backbone. This confers some degree of water miscibility though not as good as [[ethylene oxide]] based molecules.<ref>{{cite thesis | vauthors = Howarth GA | title = Synthesis of a legislation compliant corrosion protection coating system based on urethane, oxazolidine and waterborne epoxy technology | pages = 36-28, 52-60 | degree = Master of Science | date = April 1997 | publisher = Imperial College | location = London }}</ref> It is used to synthesize the [[epoxy]] [[reactive diluent]] and flexibilizer, [[Poly(propylene glycol) diglycidyl ether]].<ref>{{Cite journal | vauthors = Crivello JV |date=2006 |title=Design and synthesis of multifunctional glycidyl ethers that undergo frontal polymerization |url=https://doi.org/10.1002/pola.21761 |journal=Journal of Polymer Science Part A: Polymer Chemistry |volume=44 |issue=21 |pages=6435–6448 |doi=10.1002/pola.21761 |bibcode=2006JPoSA..44.6435C |issn=0887-624X|url-access=subscription }}</ref><ref>{{Cite patent|country=US|pubdate=1992-11-10|assign1=[[Novartis#Ciba-Geigy|Ciba-Geigy Corp.]]|number=5162547|title=Process for the preparation of glycidyl ethers|=|inventor = Roth M, Wolleb H, Truffer MA }}</ref> Another use of PPG is as a surfactant, wetting agent and  dispersant in leather finishing.<ref>{{cite journal | vauthors = Zgoła-Grześkowiak A, Grześkowiak T, Zembrzuska J, Łukaszewski Z | title = Comparison of biodegradation of poly(ethylene glycol)s and poly(propylene glycol)s | journal = Chemosphere | volume = 64 | issue = 5 | pages = 803–809 | date = July 2006 | pmid = 16343594 | doi = 10.1016/j.chemosphere.2005.10.056 | bibcode = 2006Chmsp..64..803Z }}</ref> PPG is also employed as a reference and calibrant in [[mass spectrometry]] and [[High-performance liquid chromatography|HPLC]].<ref>{{cite journal | vauthors = Rychłowska J, Zgoła A, Grześkowiak T, Lukaszewski Z | title = Isolation of poly(propylene glycol)s from water for quantitative analysis by reversed-phase liquid chromatography | journal = Journal of Chromatography A | volume = 1021 | issue = 1–2 | pages = 11–17 | date = December 2003 | pmid = 14735971 | doi = 10.1016/j.chroma.2003.09.003 }}</ref><ref>{{Cite journal | vauthors = Castillo M, Ventura F, Barceló D |date=1999-04-01 |title=Sequential solid phase extraction protocol followed by liquid chromatography–atmospheric pressure chemical ionization–mass spectrometry for the trace determination of non ionic polyethoxylated surfactants in tannery wastewaters |url=https://www.sciencedirect.com/science/article/pii/S0956053X99000045 |journal=Waste Management |language=en |volume=19 |issue=2 |pages=101–110 |doi=10.1016/S0956-053X(99)00004-5 |issn=0956-053X|url-access=subscription }}</ref> PPG and derivatives may be used as [[defoamer]]s in drilling and other applications.<ref>{{Cite journal | vauthors = Tan SN, Pugh RJ, Fornasiero D, Sedev R, Ralston J |date= February 2005 |title=Foaming of polypropylene glycols and glycol/MIBC mixtures ] |journal=Minerals Engineering |series=Reagents '04 |language=en |volume=18 |issue=2 |pages=179–188 |doi=10.1016/j.mineng.2004.08.017 |issn=0892-6875}}</ref><ref>{{Cite book | vauthors = Bava L, Mahmoudkhani A, Wilson R, Levy L |date=2013-03-23 |title=New Generation of Green Defoamers for Challenging Drilling and Cementing Applications |chapter=New Generation of "Green" Defoamers for Challenging Drilling and Cementing Applications |chapter-url=https://onepetro.org/SPEOKOG/proceedings/13POS/All-13POS/SPE-164504-MS/177686 |language=en |publisher=OnePetro |doi=10.2118/164504-MS}}</ref> It is also used as a primary ingredient in the making of [[paintball]]s.<ref>{{Cite journal | vauthors = Dhiman M, Singh K, Gupta DP, Singh DP, Upmanyu A |date=2020-05-04 |title=Study of excess acoustical and thermo-dynamical parameters of binary solutions of polypropylene glycol-400 and n-alkanols at 303 K |url=https://aip.scitation.org/doi/abs/10.1063/5.0001107 |journal=AIP Conference Proceedings |volume=2220 |issue=1 |pages=080001 |doi=10.1063/5.0001107 |s2cid=218923617 |issn=0094-243X|url-access=subscription }}</ref> It has been evaluated as a [[corrosion inhibitor]].<ref>{{Cite journal | vauthors = Solomon MM, Umoren SA, Israel AU, Etim IG |date= January 2016 |title=Synergistic inhibition of aluminium corrosion in H2SO4 solution by polypropylene glycol in the presence of iodide ions  |journal=Pigment & Resin Technology |volume=45 |issue=4 |pages=280–293 |doi=10.1108/PRT-01-2015-0010 |issn=0369-9420}}</ref>

== References ==
{{Reflist}}

==External websites==
* [https://monumentchemical.com/products/solvents-intermediates?id=558455&category_id=557047  Polypropylene Glycol (PPG) | Monument Chemical]
* [https://cameochemicals.noaa.gov/chemical/9002  POLYPROPYLENE GLYCOL | CAMEO Chemicals | NOAA]
* [https://polymerdatabase.com/polymers/polypropyleneglycol.html Poly(propylene glycol) (polymerdatabase.com)]
* [http://www.ampolymer.com/SDS/PolypropyleneGlycolSDS.html Polypropylene Glycol '''Safety Data Sheet''']

[[Category:Polyethers]]