Megasupramolecules

Dr. Julie Kornfield, Chemistry and Chemical Engineering, Caltech


19 January 2017 at 10:30

Location: BSB - B136

Megasupramolecules

 

Ultralongpolymers(weight-averagemolecularweightMw≥5000 kg/mol)exhibit striking effectson fluiddynamicsevenatlowconcentration.For example,at100 ppm, theycancontrolmistandreduceturbulentdrag,thankstotheirabilitytostoreenergyas theystretch,suchthatthefluidasawholeresistselongation.Unfortunately,ultralong backbonesundergochainscissionduringroutinehandlingbecausehydrodynamictension buildsup alongthebackbonetoalevelthatbreakscovalentbonds;this“shear degradation”continuesuntilthetheirvaluableeffectsarelost(Mw<1000 kg/mol).After

9/11,wetookafreshlookatpolymersfor mistcontrolinthehopeof discoveringa polymerthatmightmakeitimpossibletouseajumbojettobringdown askyscraper.For useinfuel,thepolymerwouldneedtobeeffectiveatverylowconcentration.Prior literatureshowedthatself-assemblyof end-associativepolymerscreatessupramolecules thatbreakandreassociatereversibly,butformationof ultra-longsupramoleculesatlow concentrationhadneverbeenachieved.Statisticalmechanicsshowedus how todesign polymersthatself-assembleintomegasupramolecules(5000kg/mol)atlow concentration(0.3%wt).  Theoreticaltreatmentof thedistributionof individual subunitsend-functionalpolymersamongcyclicandlinearsupramoleculespredicts that megasupramoleculescanformatatlowtotalpolymerconcentrationif,andonlyif,

thebackbonesarelong(>400kg/mol)andend-associationstrengthisoptimal. Viscometry andscatteringmeasurementsof longtelechelicpolymershaving polycyclooctadienebackbonesandacidor amineendgroups verifytheformationof megasupramolecules.Theyinhibitmisting(thecauseof fuelfireballs)andreducedragin thesamemannerasultralongcovalentpolymers.Withindividualbuildingblocksshort enoughtoavoidhydrodynamicchainscission(weight-averagemolecularweightsof 400 to1000 kg/mol)andreversiblelinkagesthatprotectcovalentbonds, overcomingthe obstaclesof sheardegradationandengineincompatibility.Megasupramoleculesconfera varietyof benefitsbeyondmistcontrolandarecurrentlybeingevaluatedfor commercialization.


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