lec7 silicones
TRANSCRIPT
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ChitinAntimicrobialActivity Chitinisthesecondmostabundantbiopolymerinnature..foundinthe
shellsofcrustaceans,thecuticlesofinsects,andthecellwalloffungi.
Chitosan,adeacetylated productofchitin,hasmanyinterestingproperties,suchasantimicrobialactivityandnontoxicity.Itisobtainedfromshrimpandcrabshellchitinbyalkalinedeacetylation
Biomacromolecules,2007,8 (5),pp 13591384
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SiliconeBiomaterials
SourceInformationforthefollowingslides:1)B.Ratner,A.Hoffman,F.Schoen,andJ.Lemons:BiomaterialsScience, 2ndedition(SanDiego:ElsevierAcademicPress.2004).
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SiliconeBiomaterialsChemicalStructureandNomenclature
Otherwiseknownaspolysiloxanes
Inorganicpolymerbackbonewithorganicpendantgroups
Polydimethylsiloxane (PDMS)isthemostcommonmaterialinthisclass
Inorganic/organiccombinationgivesrisetouniqueproperties Fluids,emulsions,compounds,resins,elastomers
Usedinabroadrangeofapplicationsincludingelectronics,aerospace,coatings,adhesives,andbiomaterials
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TMSterminatedPDMSmostcommonamongpolysiloxanes Linearpolymersremainliquidsevenforhighvaluesofn
Generalpropertiesofsilicones LowTg,lowtemperatureflexibility
Propertiesretainedoverawidetemperaturerange(100to250C)
Stabletohightemperatures,oxidation,chemicalandbiologicalenvironments
PropertiesaconsequenceofthelongSiObond(1.64comparedto1.54 forCC)andwideSiOSibondangle(143 comparedto109.5 forCCC)
SiObondisstrongerthanCCbond(450vs.350kJ/mol)
O Si
CH3
CH3O SiSi
CH3
CH3H3C
CH3
CH3CH3
n
(n =0, 1, 2,...)
Trimethylsilyloxy terminated PDMS
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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 81.
ShorthandNotation
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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 81.
ShorthandNotation
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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 80.
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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 82.
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SiliconeElastomers
Siliconepolymersareeasilytransformedintocrosslinked elastomersusingoneofseveralmethods
Radicalcrosslinking
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SiliconeElastomers
Siliconepolymersareeasilytransformedintocrosslinked elastomersusingoneofseveralmethods
Condensationcrosslinking
PreparedfromhydroxyterminatedPDMSandlargeexcessofmethyltriacetoxysilane
Uponexposuretomoisture,acetoxygroupsarehydrolyzedallowingcondensationofresultingsilanols
B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 83.
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Condensationcrosslinking(cont)
B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 84.
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Twopartcondensationcuringusingatetrafunctional alkoxysilane and
organotin catalyst.
Alcoholreleasedresultinginslightshrinkage
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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 85.
ElastomerFiller
Mostsiliconeelastomersincorporatefiller
Fillerreinforcesthecrosslinked matrix
Preferredfillerformostmedicalapplicationsisfumedsilica(CabOSil,
Aerosil) Reinforcementobtainedthroughhydrogenbondinginteractionofsilanol
groupsonhighsurfaceareasilicawiththesiliconepolymer
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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 85.
PhysicochemicalPropertiesofSilicones SiXandCXcompoundsbehaveverydifferently
Lowerelectronegativityofsilicon(Si 1.80vs. C 2.55) resultsinmorepolarbondscomparedtocarbon
Bondpolaritycontributestostrongsiliconbonding,i.e.SiObondishighlyionicandhasalargebondenergy.
Consequently,siliconesareresistanttohomolytic cleavage
PolarSiObondswouldleadtostrong
intermolecularinteractionswithoutprotectionofthemethylgroups. Methylgroupsinteractweaklywithoneanotherandshieldthemainchain
LowbarriertorotationaroundtheSiObondallowssiloxane chaintoadoptconfigurationthatexposesmaximumnumberofmethylgroupstoexterior
Leadstolowsurfaceenergymaterials
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SurfaceActivityofSilicones
LowbarriertorotationaroundtheSiObondallowssiloxanechaintoadoptconfigurationthatexposesmaximumnumberofmethylgroupsatmanyinterfaces Leadstolowsurfacetension
Lowsurfaceenergy
Lowintermolecularinteractions,
Resultinginalowoveralllevelofinteractionsattheirsurfaces..biocompatibility!!
PDMS lowsurfacetensionyieldscapabilityofwettingmostsurfaces
Siliconesingeneralcanwetthemselves,promotesgoodfilmformationandgoodsurfacecoverage
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Otherconsequencesoflowintermolecularinteractioninsilicones Tg verylow
Highfreevolumecomparedtohydrocarbonsresultsinhighsolubilityandhighdiffusioncoefficientofgasesintosilicones
Highpermeabilitytooxygen,nitrogen,watervapor(eventhoughliquid
watercannotwetthesiliconesurface
Compressibilityisalsohigh
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Siliconeelastomers. PeterJerschow. Shawbury,U.K.:Rapra TechnologyLtd.,2001.
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Siliconeelastomers. PeterJerschow. Shawbury,U.K.:Rapra TechnologyLtd.,2001.
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