StrongLewisacids,thatis,electronacceptors,areoftencapableofinitiatingadditionpolymerizationofmonomerswithelectron-richsubstituentsadjacenttothedoublebond①.CationiccatalystsaremostcommonlymetaltrihalidessuchasAlCl3orBF3.Thesecompounds,althoughelectricallyn...[繼續(xù)閱讀]

    Naturalandsyntheticrubberspossesssomeinteresting,unique,andusefulmechanicalproperties.Noothermaterialsarecapableofreversibleextensionof600%～700%.Noothermaterialsexhibitanincreaseinmoduluswithincreasingtemperature.Itwasrecognizedlongagothatvulcanizationwas...[繼續(xù)閱讀]

    Whenmostmaterialsaresubjectedtoaconstantshearrate(orconstantshearstress)atafixedtemperature,acorrespondingsteady-statevalueofshearstress(orshearrate)issoonestablished①.Thesteady-staterelationbetweenshearstressandshearrateatconstanttemperatureisknownasaflo...[繼續(xù)閱讀]

    Whentheflowpropertiesofpolymermeltsandsolutionscanbemeasuredoverawideenoughrangeofshearing,thelogarithmicflowcurvesappearasinFigure14.1.Itisgenerallyobservedthat:(1)Atlowshearrates(orstresses),a‘lowerNewtonian’regionisreachedwithaso-calledzero-shearviscos...[繼續(xù)閱讀]

    Engineershavetraditionallydealtwithtwoseparateanddistinctclassesofmaterials:theviscousfluidandtheelasticsolid.Designproceduresbasedontheseconceptshaveworkedprettywellbecausemosttraditionalmaterials(water,air,steel,concrete),atleasttoagoodapproximation,fit...[繼續(xù)閱讀]

    Plasticsaresyntheticorman-madematerialswhichhaveuniqueandremarkableproperties.Manydifferentplasticsmaybeobtainedbymanipulatingthemoleculesandchangingthechemicalcombinations.Plasticshaveimportantrolesinagriculture,appliances,clothing,construction,electroni...[繼續(xù)閱讀]

    ThermoplasticMaterialsItisimportanttobecomefamiliarwiththeoutstandingphysicalandchemicalpropertiesofthermoplasticplasticssoyoucanmakewiseselectionsfortheiruse.Youshouldunderstandhowandwhythesematerialscanbeprocessedincertainways.Therelationshipbetweenthep...[繼續(xù)閱讀]

    Vinylresinscoverabroadgroupofmaterialsthatrangeinpropertiesfromhardrigidproductstosoftflexibleformulations.Theyarederivedfromthe“vinyl”radical:CH2CH2.Variousatomsorsidegroupsmaybeattachedtothevinylradicaltoproducepolymersofvaryingproperties.Thelargestpoly...[繼續(xù)閱讀]

    Acopolymerofstyrene,styreneacrylonitrilehasimprovedpropertiesofstiffness,chemicalandscratchresistanceandhigherheatresistance.ItisproducedbythecopolymerizationofacrylonitrileandstyrenetoformtheSANpolymer.Duetothecopolymerization,thewater-whitecolorofpolyst...[繼續(xù)閱讀]

    Therearefewthermoplasticsthathavetheoutstandingengineeringpropertiesofpolycarbonate.Inrecentyearsithastakenitsplaceamongthemostvaluableresinsoftheindustry.Polycarbonateisamemberofthepolyesterfamilyinthatitcontainscarbonandoxygenatomsasthebackboneofthemole...[繼續(xù)閱讀]