Two- and Three-Dimensional Smectic Ordering of Single-Handed Helical Polymers
Figure1.Two-andthree-dimensionalsmecticorderingofhelicalpolymers.(A)Schematicillustrationofthehelix-senseselectivelivingpolymerizationofL-1withµ-ethynediylPt-Pdcomplex(2),yieldingamixtureofdiastereomeric,right-andleft-handedhelicalpoly-L-1’swithdifferentmolecularweightsandanarrowMWD,whichcanbefurtherseparatedintoeachsingle-handedhelicalpoly-L-1.Two-dimensional(B)and3D(C)smecticorderingoftheone-handedhelicalpoly-L-1’sonsubstrateandinLCstate.
distribution(MWD),thusformingalyotropiccholestericLCphaseinconcentratedsolutions,whosehelicalsensewasroughlydictatedbythepolymerizationsolventandtemperature.8Nolteandco-workerspreparedaseriesofpeptide-boundhelicalpolyisocyanidesstabilizedbyintramolecularhydrogenbondsfromopticallypureisocyanopeptidesusingnickeloracidcatalysts,whichresultedintheformationofasimilarcholestericLCphaseduetoitspolydispersenature.5d,6c,9HereinweshowthatthelivingpolymerizationofL-1withtheµ-ethynediylPt-Pdcatalyst(2)simultaneouslycreatesbothalmostcompletelyright-andleft-handedhelicalpolyisocyanides(poly-L-1)withadifferentmolecularweightandsufficientlynarrowMWD(Figure1A).Eachhelicalpoly-L-1canbeseparatedinafacilewayandexhibitswell-definedtwo(2D)-andthree-dimensional(3D)smecticorderingonasubstrateandinanLCstate,asdirectlyobservedbyatomicforcemicroscopy(AFM)andrevealedbyX-raydiffraction(XRD),respectively(BandCofFigure1).
ResultsandDiscussion
ThepolymerizationofD-orL-1with2([1]/[2])50,100,or200(mol/mol))astheinitiator,whichisknowntopromotethelivingpolymerizationofarylisocyanide,10wasconducted
(8)Kajitani,T.;Okoshi,K.;Sakurai,S.-i.;Kumaki,J.;Yashima,E.J.Am.
Chem.Soc.2006,128,708-709.
(9)(a)Metselaar,G.A.;Adams,P.J.H.M.;Nolte,R.J.M.;Cornelissen,J.
J.L.M.;Rowan,A.E.Chem.Eur.J.2007,13,950-960.(b)Metselaar,G.A.;Wezenberg,S.J.;Cornelissen,J.J.L.M.;Nolte,R.J.M.;Rowan,A.E.J.Polym.Sci.,PartA:Polym.Chem.2007,45,981-988.(c)Metselaar,G.A.;Cornelissen,J.J.L.M.;Rowan,A.E.;Nolte,R.J.M.Angew.Chem.,Int.Ed.2005,44,1990-1993.(d)Cornelissen,J.J.L.M.;Graswinckel,W.S.;Rowan,A.E.;Sommerdijk,N.A.J.M.;Nolte,R.J.M.J.Polym.Sci.,PartA:Polym.Chem.2003,41,1725-1736.(e)Cornelissen,J.J.L.M.;Sommerdijk,N.A.J.M.;Nolte,R.J.M.Macromol.Chem.Phys.2002,203,1625-1630.(f)Cornelissen,J.J.L.M.;Donners,J.J.J.M.;deGelder,R.;Graswinckel,W.S.;Metselaar,G.A.;Rowan,A.E.;Sommerdijk,N.A.J.M.;Nolte,R.J.M.Science2001,293,676-680.
(10)(a)Takei,F.;Hayashi,H.;Onitsuka,K.;Kobayashi,N.;Takahashi,S.
Angew.Chem.,Int.Ed.2001,40,4092-4094.(b)Onitsuka,K.;Joh,T.;Takahashi,S.Chem.Eur.J.2000,6,983-993.(c)Onitsuka,K.;Joh,T.;Takahashi,S.Angew.Chem.,Int.Ed.Engl.1992,31,851-852.230J.AM.CHEM.SOC.
9
intetrahydrofuran(THF)at55°Candquantitativelyproducedrodlikehelicalpolyisocyanides([D-orL-1]/[2])100forpoly-D-1orpoly-L-1,[L-1]/[2])50forpoly-L-150,and[L-1]/[2])200forpoly-L-1200).Sizeexclusionchromatography(SEC)ofpoly-L-1detectedbyUV(254nm)andcirculardichroism(CD)(364nm)revealedabimodaldistributionwithasharpmainpeaktogetherwithasmallpeakinthelowermolecularweight(Mw)regionwhoseCDsignswereopposite,negative,andpositive,respectively(Figure2A),suggestingamixtureofright-andleft-handedheliceswithdifferentMw’s.Wefoundthateachhelicalpoly-L-1couldbeeasilyseparatedbyfractionationwithacetoneintoacetone-insolubleand-solublefractionswhichshowedunimodalchromatogramswithnegativeandpositiveCDsignsat364nmforthehigh-Mwpoly-L-1(-)andlow-Mwpoly-L-1(+),respectively(BandCofFigure2).TheCDspectraofpoly-L-1(-)andpoly-L-1(+)inthen-π*transitionoftheiminochromophoreregionsofthepolymerbackbones(280-480nm)aswellasinthependantaromaticregions(240-280nm)10,11arealmostmirrorimagesofeachotherwithagreaterintensitythantheintensityofthosebeforethefractionation(Figure2D).Theseresultsindicatethattheas-preparedpoly-L-1isindeedamixtureofright-andleft-handedhelices.12Wenotethattheyarenotenantiomers,butdiastereomerswitha
(11)(a)Hase,Y.;Mitsutsuji,Y.;Ishikawa,M.;Maeda,K.;Okoshi,K.;Yashima,
nJ.2007,2,755-763.(b)Ishikawa,M.;Maeda,K.;Mitsutsuji,Y.;Yashima,E.J.Am.Chem.Soc.2004,126,732-733.(12)ThedifferenceintheMw’sofpoly-L-1(-)andpoly-L-1(+)canbeexplained
onthebasisofthedifferenceinpropagationratesofthetwogrowingspecies,givinghigh-andlow-Mwpolymers,respectively.Plotsofthenumber-averagemolecularweight(Mn)ofleft-handedhelicalpoly-L-1(-)andright-handedhelicalpoly-L-1(+)versusfeedmolarratioofthemonomerL-1totheinitiator(2)([L-1]/[2])gaveanalmostlinearcorrelation(FigureS10),whichisindicativeofamechanisminwhichdiastereomericoligomersofL-1withbothhelicalsensesareformedduringtheinitialstageofpolymerizationandoneofthetwoappearstopropagaterapidlyovertheother,producingright-andleft-handedhelicalpoly-L-1’swithdifferentMw’s.ThereasonwhydiastereomericoligomerswithbothhelicalsensesareformedduringtheinitialstageofpolymerizationofL-1isnotclearatpresent,butitmaybecorrelatedwiththepreviousobservationsthattheconventionalpolymerizationofL-1withNiCl2asacatalystproducedpoly-L-1’s,whosehelicalsenseswereconsiderablyinfluencedbythepolymer-izationsolventandtemperature.
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