Improvement of corrosion protection of steel by incorporation of a new phosphonated fatty acid in a phosphorus-containing polymer coating obtained by UV curing

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T

OULOUSE

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uverte (

OATAO

)

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To link to this article : doi:

10.1016/j.porgcoat.2013.10.002

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http://dx.doi.org/10.1016/j.porgcoat.2013.10.002

To cite this version : Millet, France and Auvergne, Rémi and Caillol,

Sylvain and David, Ghislain and Manseri, Abdelatif and Pébère,

Nadine Improvement of corrosion protection of steel by incorporation

of a new phosphonated fatty acid in a phosphorus-containing polymer

coating obtained by UV curing. (2014) Progress in Organic Coatings,

vol. 77 (n° 2). pp. 285-291. ISSN 0300-9440

Any correspondance concerning this service should be sent to the repository

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Improvement

of

corrosion

protection

of

steel

by

incorporation

of

a

new

phosphonated

fatty

acid

in

a

phosphorus-containing

polymer

coating

obtained

by

UV

curing

France

Millet

_,

_Rémi

_Auvergne

_,

_Sylvain

_Caillol

_,

_Ghislain

_David

_,

Abdelatif

Manseri

_,

_Nadine

_Pébère

a_{UniversitédeToulouse,CIRIMAT,UPS/INPT/CNRS,ENSIACET,4alléeEmileMonsoBP44362,31030ToulouseCedex4,France}

b_{InstitutCharlesGerhardtUMRCNRS5253,LaboratoireIngénierieetArchitectureMacromoléculaire,EcoleNationaleSupérieuredeChimiedeMontpellier,}

8ruedel’EcoleNormale,34296MontpellierCedex05,France

Keywords:

Phosphonatedmethacrylate Coating

Phosphonatedfattyacid Inhibitor

Electrochemicalimpedancespectroscopy

a

b

s

t

r

a

c

t

Sixformulationscontainingdiacrylatemonomers(from89to92.5%(w/w))aswellasaphosphonated

methacrylatemonomer(from1to10%(w/w))wereprepared.AllformulationswereUV-curedandthe

corrosionperformanceoftheresultingcoatingsappliedontoasteelsubstratewasassessedby

elec-trochemicalimpedancespectroscopy(EIS).Itwasfirstshownthatthecoatingscontainingphosphonic

acidmethacrylate(MAPC1(OH)2)insteadofmethacrylatephosphonicdimethylester(MAPC1)presented

highercorrosionprotectionrelatedtothestrongadhesivepropertiesofphosphonicacidonthemetal

substrate.AminimumMAPC1(OH)2contentof2.5%wasdeterminedtoprovidethehighestimpedance

values(bestefficiency).Then,anewbio-basedcompound,i.e.phosphonicacid-bearingoleicacid

(phos-phonatedfattyacid),wassynthesizedandaddedasaninhibitortotheformulations.Inthepresenceof

thiscompound,thecorrosionprotectionwasnotablyimproved.Thebeneficialeffectofphosphonated

fattyacidwasexplainedbyitsinhibitiveactionatthesteel/coatinginterfaceandbytheimprovementof

thebarrierproperties.

1. Introduction

Inrecentyears,phosphorus-containingproductshavegained significantdevelopmentduetotheirinterestingpropertiesin var-ious applications. For example, dental adhesives, ion-exchange resinsand adhesion promotors are three ofthe more common applications[1–7].Furthermore,flameretardantscontaining phos-phorus atoms progressively came to replace halogenatedones [8–12].Phosphorus-containingcompoundsareexcellent promo-tors withrespecttoadhesion,and thus improve anti-corrosion effects.Commercialanti-corrosionpolymersaregenerallyformed from Sipomer® _{or Phosmer}® _{monomers, which are}

phosphate-type(meth)acrylates,andcanbereadilypolymerizedviaemulsion or solution [13,14]. Sheffer et al. [15] reported the enhanced corrosionprotectionof sol–gelfilmsonaluminum substrateby entrappingphosphonategroupinorganosilanes.However, phos-phonategroupswhichremainasadditivesinaphysicalmixture can lead to dynamic phenomena such as aggregation, phase separation or leaching by solvent or water with time. Such

∗ Correspondingauthor.Tel.:+33534323423. E-mailaddress:nadine.pebere@ensiacet.fr(N.Pébère).

disadvantages can be overcomeif the phosphonates form part ofpolymer network.Kannanetal.[16,17]reportedthe synthe-sisofahighlycross-linkedmethacrylate-phospho-silicatehybrid bycopolymerizing2-(methacryloyloxy)ethyl phosphate(EGMP), containing a polymerizable methacrylate group and functional phosphategroupwith3-[(methacryloyloxy)propyl] trimethoxysi-lane(MEMO)whichpossessesapolymerizablemethacryloxygroup atoneendandalkoxysilanegroupscapableofforminginorganic networksvia sol–gelrouteat theotherend.Protection ofsteel substrateswiththesehybridcoatingswasexplainedbythestrong interfacialacid–baseinteractionsofP–O−_{groupsfromphosphate}

withtheMn+_{fromthemetalsubstrate[17].Polymerswithsome}

phosphonatefunctionalityhavelongbeenestablishedasexcellent adhesivesandanti-corrosioncompounds[18–25].However,there hasbeenverylittleinvestigationintotheuseofphosphonate-type methacrylatesforthesamepurpose[13,14,26].Inaneffortto syn-thetizenewtypesofphosphonatedmethacrylatemonomers,we haveproposedaseriesofmonomerswiththefollowinggeneral formula: CH2 C(CH3)C(O)O(CH2)nP(O)(OR1)(OR2).The synthesis

wasachievedbyusingseveralorganicpathwayssuchasthe well-knownArbusovreaction[27,28]orbyusinghydroxyl-phosphonate compoundsunderSchotten–Baumanconditions[29]endingwith methacrylates bearing spacer n values from 1 to 11. More

recently, new N,N-amino-bisphosphonic-containing methacry-lates (MACnNP2) [30] and new gem-bisphophonic-containing

methacrylates(MACnP2)[31]havealsobeensynthesizedand

poly-merizedunderUV-light.Theresultingcoatings,evaluatedbysalt spraytest,showedefficientcorrosionprotectionofsteelafterover 900h of exposure. Posner et al. [32] already reported UV cur-ablecoatingsbasedonacrylate/styrenecopolymerstobeefficient againstcorrosion, but no phosphonate-containingmethacrylate compoundhasbeenusedsofar.

Theaimof the presentstudy wastoevaluate thecorrosion protectionof coatingsobtained from UV polymerization based on (meth)acrylate compounds and more specifically diacrylate monomersaswellasphosphonatedmethacrylatemonomers.The coatingswereappliedon a steelsubstrate and thebehavior of thesteel/coatinginterfacewascharacterizedduringimmersionin 0.1MNaClbyelectrochemicalimpedancespectroscopy[33–37]. Inthefirstpartofthestudy,theinfluenceofthephosphonicacid methacrylatecontentonthecorrosionprotectionwasinvestigated. Then,inasecondstep,anewphosphonatedfattyacidwas synthe-sizedandaddedtotheformulationpriortotheUVpolymerization. NotethatthismoleculedoesnotparticipateintheUVcross-linking withacrylatemonomersbutwasincorporatedintheformulation asaninhibitivecompoundtoenhancethecorrosionprotectionof thesteel.

2. Experimental 2.1. Materials

AllchemicalswerepurchasedfromAldrichandusedwithout furtherpurification.

Two phosphonated methacrylate monomers MAPC1 and MAPC1(OH)2weresynthesizedaccordingtoapreviouslydescribed

procedure[26].TheirchemicalstructureisshowninFig.1. Low-carbon steel Q-Panel plates (SAE1008/1010, R type) 150mm×75mm×0.8mmwereusedassubstrate.

2.2. Synthesisofanewphosphonatedfattyacid(phosphonic acid-bearingoleicacid)

Inafirststep,thephosphonationofmethyloleatewascarried outinaglassreactorcontaining0.249g(0.00170mol)of di-tert-butylperoxide,10g(0.034mol)ofmethyloleateandtwomolar equivalents of dimethyl phosphite. The mixture washeated to 125◦_{Cfor12h.Aftercoolingtoroomtemperature,excessdimethyl}

phosphite wasremovedunder highvacuum.Phosphonic ester-bearing oleic methyl ester was obtained with 78% yield. This synthesiswasperformedbySpecificPolymersandsoldunderthe SP-3S-10-001trademark.

1_HNMR(CDCl

3,ı,ppm):3.70(d,6H,PO(OCH3)2),3.63(s,3H,

COOCH3), 2.26(t,2H, CH2-COOCH3), 0.84 (t, 3H, CH3-CH2).31P

(CDCl3,ı,ppm):37.7.

Inasecondstep,10g(0.025mol)ofphosphonicester-bearing oleic methylester and 50g of dioxanewere introduced into a single-necked round bottom flask equipped with a condenser

Fig.1.Structuresofthemonomers:(a)methacrylatephosphonicdimethylester (MAPC1)and(b)phosphonicacidmethacrylate(MAPC1(OH)2).

Table1

Compositionofthedifferentformulationspreparedfortheelectrochemical charac-terization.Eachformulacontains6%Darocur.

Formulation Acrylates (wt.%) MAPC1(wt. %) MAPC1(OH)2 (wt.%) Newphosphonated fattyacid(wt.%) 1 92.7 1.3 – – 2 92.7 – 1.3 – 3 91.5 – 2.5 – 4 89 – 5 – 5 84 – 10 – 6 89 – 2.5 2.5

and a magneticstirrer.Subsequently, two molarequivalents of hydrochloricacidwereaddeddropwise.Then,thesolutionwas vig-orouslystirredunderdioxanerefluxingfor6h.Afterpurification, phosphonicacid-bearingoleicacidwasobtainedwith55%yield. Thissynthesiswasperformedbyspecificpolymersandsoldunder theSP-3S-10-009trademark.

1_HNMR(CD

3OD,ı,ppm):5.03 (s,4H,PO(OH)2),2.30 (t,2H,

CH2-COOH),0.92(t,3H,CH3-CH2).31P(CD3OD,ı,ppm):33.2.

The chemical structure of the products was determined by

1_{H and} 31_{P NMR(Bruker AC400MHz)atroom temperaturein}

CDCl3 solutions.Abbreviationss,d,t,q,mstandforsinglet,

dou-blet,triplet,quadrupletandmultiplet,respectively.TheINVGATE procedurewithdelayD1of 10swasusedtoquantify thefinal yield.

2.3. UVphotopolymerizationofmethacrylatemonomersand coatingpreparation

TheUVpolymerizationof mixturesof(meth)acrylates (com-posedoftripropyleneglycoldiacrylate,hexanedioldiacrylateand phosphonatedmethacrylateMAPC1orMAPC1(OH)2),andDarocur

1173(6%,w/w)asaphotoinitiatorwasstudiedbyrealtimeFT-IR spectroscopywithaNicoletNexusapparatuswith2cm−1

accu-racyusingOMNICsoftware.TheUVintensitywasmeasuredusing aSolatellUVspectroradiometerapparatus(4DControlsLimited, Cornwall,UK).Thekineticsof(meth)acrylate monomer conver-sionhavealreadybeenpublished[38].Thereagentswereblended without solvent.Six different formulations wereprepared. The compositionsareindicatedinTable1.Thefirstcomposition(F1) wascomposedofacrylates,MAPC1andphotoinitiator,whilethe foursubsequentcompositions(F2–F5)containedacrylatesand var-ious amounts of theMAPC1(OH)2 with photoinitiator. The last

formulation(F6)contained2.5%MAPC1(OH)2aswellas2.5%new

phosphonatedfattyacid.

Thesteelsubstratesweredegreasedwithmethylethylketone (MEK) and dried in warmair for 30min. Then, theliquid for-mulationwasuniformlyappliedonthesteelsampletoobtaina uniformlayeraftercuring.ThefilmswereappliedwithaSHEEN barcoater.Coatedsampleswerethenphotopolymerized.TheUV sourcewasplacedperpendiculartothesamplesurfaceandinduced thecrosslinkingreaction,monitoredinreal-timeviaFT-IR. Com-pleteconversionofmonomertopolymerwasobtainedafterca.60s, confirmedbyfollowingtheintensityofIRabsorptionat812cm−1

(characteristicoftheC C methacrylatemonomerdoublebond). Thedryfilmthicknesswas20±2mm(measuredbyaBykotest7500 digitalmeter).

2.4. Electrochemicalmeasurements

A three-electrode electrochemical cell was used in electro-chemicalimpedancemeasurements.Acoatedspecimenwasused asworkingelectrode.AcylindricalPlexiglastubewasassembled ontopofthecoatedsample(exposedsurfacearea:29cm2_)and

filledwiththeaggressivesolutionpreparedfromdistilledwater byadding0.1MNaCl(reagentgrade).Alargeplatinumsheetand asaturatedcalomelelectrodewereusedascounterandreference electrodes,respectively.Theelectrochemicalcellwaskeptatroom temperatureandopentoair.Electrochemicalimpedance measure-mentswerecarried outusing a Solartron1287electrochemical interfaceconnectedtoaSolartron1250frequencyresponse anal-yser.Impedancediagramswereobtainedoverafrequencyrangeof 65kHztoafewmHzwithsixpointsperdecadeusinga20mV peak-to-peaksinusoidalvoltage.Thelinearityofthesystemwaschecked byvaryingtheamplitudeoftheacsignalappliedtothesample.The electrochemicalbehaviorofthesteel/coatingsinterfacewas char-acterizedfordifferentexposuretimestotheaggressivesolution rangingfrom2hto72h(3days).

2.5. Scanningelectronmicroscopy(SEM)observations

SEM,coupledwithX-raydiffraction(SEM-EDX),wasusedto visualize the morphology of the coatings and define localized concentrationsofphosphorus.Analyseswereperformedon cross-sectionsofthecoatingmaterial.SEM-EDXanalyseswereperformed usingaLEO435VPelectronmicroscopeoperatingat8kV.The phos-phorusprofileswereobtainedfrom64measurementsthroughthe wholecoatingthickness.

3. Resultsanddiscussion

Impedance measurements were performed to evaluate the effectsofthephosphonatedmethacrylatemonomersonthe cor-rosionprotectionofthesteelcoatedbythedifferentformulations. First, the influence of the methacrylate monomers (MAPC1 or MAPC1(OH)2)wasinvestigated.Then,theinfluenceoftheaddition

ofthenewphosphonatedfattyacidwasstudied.Itcanbe men-tionedthatcorrosionappearedrelativelyrapidlyindicatingthat thecoatingsofferedalowcorrosionprotection.Albeit unsatisfac-toryitishelpfultorapidlydiscriminatetheeffectoftheadditives. Forthisreason,theimpedanceresultswerecomparedforonly24h ofimmersionintheNaClsolution.

3.1. Theeffectofboththenatureandthecontentofthe phosphonatedmethacrylatemonomer(esteroracidgroups)on corrosionprotection

Fig.2reports theimpedancediagramsobtainedafter24hof immersioninthe0.1MNaClsolutionforthetwoformulations(F1 andF2).Thediagramsarecharacterizedbytwo timeconstants: thehigh-frequency(HF)partofthediagrams(from105_to1Hz)is

relatedtothecoatingandattributedtothebarrierpropertiesof

102 103 104 105 106 107 108 0 20 40 60 80 10-3 10-2 10-1 100 101 102 103 104 105 F2 F1 Impedance modulus / Ω c m 2 Phase angle / degree Frequency / Hz

Fig.2.Electrochemicalimpedancediagrams(Boderepresentation)obtainedforthe F1andF2samplesafter24hofimmersionin0.1MNaClsolution.

0 2 106 4 106 6 106 8 106 1 107 2 3 4 5 Z3 m H z / Ω c m 2 Formulation

Fig.3.|Z|3mHzafter24hofimmersionin0.1MNaClsolutionfortheformulations

withdifferentMAPC2(OH)2concentrations.

thefilm,whilethelow-frequency(LF)part(from1to10−3_Hz)

cor-respondstothereactionsoccurringatthemetal/coatinginterface throughdefectsandporesinthecoating[39,40].FortheF1 coat-ing,thebarriereffect(HFrange)issignificantlylowerthanforthe F2coating:theimpedancevalueisonly2×104_cm2_(plateauin

theHFrange).Inaddition,theimpedancemodulusat3mHzislow whichindicatesthattheF1coatingispoorlyefficientatprotecting thesteelsurfacewhichisalsoaconsequenceofthepoorbarrier effect.ThediagramfortheF2coatingrevealsahigherimpedance modulusintheHFrange(2×106_cm2_{)comparedtoF1indicating}

thatthebarriereffectwasimproved.Thebarriereffectleadstoa decreaseofthesurfaceareaincontactwiththeelectrolyte(high impedancemodulusintheLFrange)andasaconsequencecoating F2wasmoreprotective.

Fromthisfirstsetofexperiments,itcanbeconcludedthatthe coatingcontainingacidmethacrylateinsteadofestermethacrylate conferredamoreefficientcorrosionprotectiontothemetal sub-strate.Thus,inthereminderofthestudyonlyMAPC1(OH)2 was

used.

Theinfluence oftheMAPC1(OH)2 contentin thecoatingfor

thecorrosionprotectionofthesteelwasinvestigated.Similar for-mulationswerepreparedandonlytheMAPC1(OH)2contentwas

changed(1%,2.5%,5%and10%).Theimpedancediagramspresented thesameshapeandarenotreportedhere.Itcanbementionedthat theHFpartoftheimpedancediagramswaspoorlymodifiedinthe presenceofdifferentMAPC1(OH)2concentrationsandonlytheLF

partchanged.ThisresultindicatesthatMAPC1(OH)2actsmainlyat

themetal/coatinginterface.ItwasproposedbyKitteletal.[41]and thegroupofBierwagen[42–44]thattheimpedancemodulusatlow frequencies(|Z|3mHzinthepresentstudy)couldserveasan

esti-mationofthecorrosionprotectionofapaintedmetal.Fig.3reports |Z|3mHzafter24hofimmersionintheNaClsolutionforthefour

for-mulationswithdifferentMAPC1(OH)2contents.Itcanbeseenthat

theimpedancemodulusisthehighestfortheF3formulation(2.5%) anddecreaseswhentheMAPC1(OH)2concentrationincreases(F4

andF5).However,thedecreaseisnotsignificantandthedatain Fig.2allowaminimumefficientMAPC1(OH)2concentrationtobe

determined.Thisconcentrationisaround2.5%.

3.2. Influenceoftheadditionofnewphosphonatedfattyacidon thecorrosionprotectionofcoatedsteel

3.2.1. Newphosphonatedfattyacid

In the present study, the phosphonation of methyl oleate wasinvestigated.Thechemicalincorporationofphosphonicacid moitiesontomethyloleatewasdoneviaatwo-steppathway,as depictedbelow:

Fig.4.1_HNMR(CDCl

3)ofphosphonate-bearingmethyloleate. (a)

Fig.5.1_HNMRand31_PNMR(CDCl

102 103 104 105 106 107 108 0 20 40 60 80 10-3 ₁₀-2 ₁₀-1 ₁₀0 ₁₀1 ₁₀2 ₁₀3 ₁₀4 ₁₀5 F6 F3 F4 Impedance modulus / Ω c m 2 Phase angle / degree Frequency / Hz

Fig.6.Electrochemicalimpedancediagrams(Boderepresentation)obtainedfor samplesF3,F4andF6after24hofimmersionin0.1MNaClsolution.

Thefirststepcorrespondstotheradicaladditionofdimethyl phosphite ontotheunsaturated C C of theacid.Aswith thiol-eneradicalcoupling[45],radicaladditionofmethyloleate(MO) withdimethylphosphite,usedaschaintransferagent(CTA),was carriedoutathightemperaturewithanexcessofCTAcompared todoublebond.Inthesereactionconditions,phosphonationwas accomplishedafter12handtheresultingMO-phosphonatewas obtainedat about80%yield. In Fig.4, 1_{H NMR shows thatthe}

CH3protonsofthemethylphosphonateesterappearat3.70ppm.

Moreover,thevinylprotonsofMO,centeredat5.34ppm,areno longerpresent,indicatingsuccessfulphosphonation.Furthermore,

31_{PNMRshowedasinglepeakcenteredat37.7ppm(notreported}

here).

Phosphonated fatty acid was obtained in a second step by hydrolysisofmethylestergroupsofphosphonatemoietieswith hydrochloricacidinadioxanesolution.Inthesereaction condi-tions,themethylesterofmethyloleatewasalsohydrolyzedto leadtothecorrespondingcarboxylicacid.Fig.5showsthe1_HNMR

and31_{PNMRspectraofthephosphonatedfattyacid.TheCH}

3

pro-tonsofthemethylphosphonateester,centeredat3.70ppm,areno longerpresent,indicatingsuccessfulhydrolysis.Insupportofthis, thepeakofP O CH3at37.7ppmisshiftedto33.2ppmforP OH.

3.2.2. Thecorrosionprotectionofcoatedsteelwiththeadditionof oleicacidphosphonicacid

ItwasseenthatinthepresenceofmethacrylateMAPC1(OH)2,

thehighestimpedancevaluewasobtainedwhenitwas incorpo-ratedintotheformulationataconcentrationof2.5%(F3coating). The performance of the coating containing the phosphonated fattyacid(F6formulation)wascomparedtotheF3coating.The impedancediagramsobtainedafter24hofimmersionintheNaCl solutionarereportedinFig.6.TheimpedanceoftheF4coating(5% MAPC1(OH)2)isalsoshowninordertoseparatetheroleplayed

Fig.8.SEMmicrograph(cross-section)forcoatingF6.

bytheadditionofthephosphonatedfattyacidandtheroleofthe acidinthemethacrylateMAPC1(OH)2.ItcanbeseeninFig.6,that

theadditionofphosphonatedfattyacidimprovedthebarrier prop-ertiesofthecoating.FortheF3andF4coatings,theimpedance valuesintheHFrangewerebetween2×106 _and3×106_cm2_.

Withtheadditionofthephosphonatedfattyacid,theimpedance valueintheHFrangewasabouttentimeshigher(2×107_cm2_).

Theimpedancemodulusat3mHzwas4×107_cm2_showingthat

thecorrosionprotectionwasimproved.

Photographsoftheelectrodesurfaceweretakenattheendof theelectrochemicaltest(72hofimmersionintheNaClsolution) andareshowninFig.7.ThesurfaceofcoatingF6appearspoorly corroded,andincontrast,thesurfacesofthecoatingsF3andF4 aredamagedandcorrosionproductsareclearlyvisible.The pho-tographscorroboratetheelectrochemicalresultsandunderlinethe beneficialeffectoftheadditionofphosphonatedfattyacidonthe corrosionprotectionofthesteelsurface.

Toanalyzetheroleofphosphonatedfattyacid,SEM/EDX analy-seswereperformed.Theaimwastodetectthephosphorusthrough thewholecoatingthicknessandparticularlyatthemetal/coating interfaceandtoshow(ifpossible)aphosphorusgradient concen-tration.Foreachsampletwodifferentzoneswerestudied.Fig.8 showsacross-sectionoftheF6coating.Thecoatinghasauniform thickness.PhosphorusprofileswereobtainedforF4andF6coatings (Fig.9).InFig.9a,itcanbeseenthatthroughthewholecoating thickness,thequantityofphosphorusisconstant.Aprogressive decreasecanbeobservedattheouterpartofthecoatingwhichcan beexplainedbytheSEMproberesolution.Incontrast,inFig.9b,the phosphorusprofilesaresignificantlymodifiedatthemetal/coating interfaceandrevealahigherphosphoruscontent.Itcanbeseen thatabout3mmoftheinternalzoneofthecoatingwasenriched inphosphorus.However,EDXisnotasuitabletechniqueto deter-minethethicknessofthisinterfacialzoneaccurately.Thedifference betweenthetwosamples(Fig.9aandb)wasonlythepresenceof thephosphonatedfattyacid.Thus,itcanbeconcludedthatinthe F6coatingthephosphonatedfattyacidcanmigratethroughthe

0 200 400 600 800 1000 20 15 10 5 0 F4 coating Counts number Coating thickness / µm Metal/coating interface 0 200 400 600 800 1000 20 15 10 5 0 F6 coating Counts number Coating Thickness / µm Metal coating interface

Fig.9.PhosphorusprofilesalongthecoatingthicknessforcoatingsF4andF6(,♦: resultsoftwoindependentmeasurementsonthesamesample).

filmandreachthesubstratetoinhibitthecorrosionofthesteel [46,47].Asaconsequence,corrosionresistancewasimproved.It canbenotedthatthephosphoruscontentwashigherfortheF4 coatinginagreementwiththehigherMAPC1(OH)2content.

4. Conclusions

Differentformulationscontainingdiacrylatemonomers, phos-phonicmethacrylateandanewlysynthesizedphosphonatedfatty acidweredepositedonacarbonsteelsubstrateandpolymerized byUVcuring.Thecorrosionprotectionaffordedbythedifferent coatingswasinvestigatedbyEIS.Fromtheimpedancedata,itwas foundthat:

(i)Phosphonicacidmethacrylateprovidedhighercorrosion resis-tanceincomparisonwithestermethacrylate.

(ii)Thebestcorrosionprotectionwasobtainedwith2.5% phos-phonicacidmethacrylate.Anincreaseoftheconcentrationdid notimprovethecorrosionresistanceofthesteel.

(iii)Theadditionofthesynthesizedphosphonatedfattyacidinthe formulationsignificantlyenhancedtheprotectiveproperties ofthecoating.Thisperformancewasexplainedbyboththe bar-rierpropertiesandthecorrosioninhibitionatthesteelsurface duetothepresenceofthephosphonicgrouponthemolecule. Finally,integratingphosphonatedfattyacidinabio-based coat-ingusingvegetableoils[48]seemstobepromising.Thisstudyis stillunderinvestigationandshouldbethesubjectofaforthcoming publication.

Acknowledgments

TheauthorsgratefullyacknowledgeYannickThebaultforhis mostvaluableassistanceintheareaofSEM-EDX.Theauthorsalso

gratefullyacknowledgeSpecificPolymersforprovidingthe phos-phonatedfattyacidmolecule.

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