Properties and Processing of Engineering Materials
Properties and Processing of Engineering Materials MATSE 259
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Date Created: 11/01/15
Topics to be Covered Elements of Addition Polymerization Brarzching and T acticity The Effect of Crystallinity orz Properties Chapters 1 d 2 in CD Polymer Science and Engineering What Are Polyolefins The term polyole n embraces all polymers that are derived from simple unsaturated aliphatic hydrocarbons that contain one double bond per monomer Examples include The most important polyole ns in terms of production volume are polyethylene PE polypropylene PP and the ethylenepropylene copolymers EP Other signi cant polyole ns include polybutlene poly4methylpentlene and polyisobutene PIB Low Density Polyethylene 1890 s j CHzNz 39CH2n 39 N2 1930 s ICI chemical reactions under pressure Ethylene Benzaldehyde r Low Density Polyethylene 394va a v a k mx a A modern cable coating The original ICI pilot plant This allowed l I mi p 39 quotE ll 39 gammamm mun mm LG5139 ITSHIEHSNLE up TO TUV39O39LDGK U5T quotMT FDQLWI OG I I am ruumsamcuimr runrlmumT um urns 39 Tun mmnm mu 71 um Em HAIEIERS 8H1 BACH TO THE ru nmmu Tun mm m uim39 1 mm Mm Low Density Polyethylene Chain Polymerizations Monomers Polymer One type of Plus residual re c monomer and monomer A R I very sma 7 amountl of growing chains A 39 Characteristics of Chain Polymerizations Need 1 0 consider H Ressszsamc z 9 gquot 1 Im a on x x 2 Propagafion 3 Terminafion Rest of Chain I ll 4 Chain Transfer CH239 CgC zg Active site Chain Polymerizations Various Olefins and CH2 CHX mel Monomers CH2 CX CH CH2 Various Dienes C H C H Acetylene C I Caprolactam N c z H2 Ethylene Oxide Izat Polymer Chain Ic view list Chain Polymerizations H Rest of Chain 39 C39 X R t fc 39 922J 239L39CHZ clH CHz X gtlt9 Chain Polymerizations Types nature of the active site H ReSJSLSILal39LCHZ fc f 9quot Free Radical x x Anionic H m Cationic R t f c 39 es3amCH2 9 CH2 9H Coordmatlon Catalyst X X Anion or Cation 39139 Re L ZfJ l EE39CHZ elll CH2 9 X X Characteristics of Chain Polymerizations Need 1 0 consider H ReSJSLS39L 39LCHZ 9 CH2 9quot 1 Inifiafion x x 2 Propagafion Active site 3 Terminafion H Rest of Cham 4 Chain Transfer Iclir X X Free Radical Polymerization Initiation INITIATION ROOR gt 2R0 Peroxide Peroxide Radical RO CH2CHX gt quot39 ROCHzC 2 Free Radical Polymerization Propagation H Rest of Chain 39 quotquotquotquotquotquotquotquotquotquot CH2 C39 C 2 9H Rest of Chain IHcHz Free Radical Polymerization Termination H H Rest of Chain 39 39 Rest of Chain cl cl X X cH2 CH2 X X Rszwsbziquot 2 Re558121mc CHX Hzxc CHZ39ESLBLEPE Short Chain Branching in Polyethylene CH2 CH2 CH2 CH CH2 H CH2 Formafion of shorf chain branches in polyefhyene CHz CH2 CH2 CH CHZ CH2H CH2 CH2 C4H9 C4H9 CH2 CH CH2 CH2 gt CH2 CH CH2 CH2 CH2 CH2 CH2 CH2 Linear and Branched Polymers Linear Branched z z z Crystallinity in Polymers Let39s establish a simple connection between structure and properties right from the beginning We39ll explore polymer morphology in more detail later but simplistically we can get RANDOM C OILS SEMI CR YS T ALLINE POL YMERS Like cooked spaghetti A bit like quotuncooked spaghetti The Effect of Crystallinity on Properties We will be asking how crystallinitj affects S rr39eng rh S riffness Toughness Bar39r39ier39 ProperTies Soubi Ii ry Tr39anspar39ency Ther39ma Pr39oper39Ties ETc Linear and Branched Polymers Linear Branched z z z Which of fhese is more likely f0 crysfallize The answer is linear 39 Various grades of polyeThylene are produced commercially and are ofTen referred To as high densiTy or low densiTyquot Which do you Think is The high densiTy polyeThylene A The linear more crystalline stu B The somewhat branched less crystalline stu The answer is still linear Chains ThaT cannoT cr39ysTallize eg highly branched ones or39 even linear chains ThaT ar39e heaTed above Their39 cr39ysTalline melTing poinTs acTually look someThing like cooked spagheTTi or39 random coils n They do noT pack as closely TogeTher as in The cr39ysTalline sTaTe The Effect of Crystallinity on Proportles The Type of polyeThylene ThaT goes inTo milk Jugs is sTronger sTiffer buT more opaque less opTically clear Than The Type of polyeThylene ThaT is used To make film wrap greaTer opTical clariTymore flexible buT less sTrong Can you figure ouT which Type of polyeThylene is used To make film wrap A High densiTy B Low densiTy Property Change with Increasing Degree of Crystallinity IIIIIIIIIIIIIIIIIiIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Strength E Generally increases with degree of crystallinity IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Stiffness Generally increases with degree of crystallinity IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Toughness Generally decreases with degree of crystallinity IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Generally decreases with increasing degree of crystallinitySemicrystalline polymers usually appear opaque because of the difference in refractive index of the amorphous and crystalline domains which leads to scattering Will depend upon crystallite size IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Small molecules usually cannot penetrate or diffuse through the crystalline domains hence barrier propertiesquot which make a polymer useful for things like food wrap increase with degree of crystallinity Optical Clarity Barrier Properties IIIIIIIIIIIIIIIII Similarly solvent molecules cannot penetrate the crystalline domains which must be melted before the polymer will dissolve Solvent resistance increases with degree of crystallinity Solubility What is the Problem with Propylene First The Metal Oxide Catalysts and Linear Polyethylene Hogan and Banks synthesized polypropylene and linear polyethylene in a low pressure process using metal oxide catalysts A Company Maker The Hula Hoop The French can make even polyethylene look sexy Ziegler and Natta Ziegler and the Organometallic Catalysts In his lecture at the Nobel Prize award ceremony Ziegler described his preliminary worka thus The development began at the end of 1953 when Holzkamp Breil Martin and myself in a few almost dramatic days observed that the gas ethylene could be polymerized at 100 20 or 5 atmospheres and finally even at atmospheric pressure very rapidly in the presence of certain easily prepared catalysts to give a high molecular weight plastic High Pressure Ziegler Metal Oxide Polyethylene Polyethylene Polyethylene Molecular Weight Mn 20000 15000 15000 Number of Me groups1000 Carbons 30 6 lt 015 Density gcc 0 92 0 95 0 96 Crystalline Melting Point C 108 130 133 Natta and Stereoregularity In the middle of 1954 Natta and his coworkers having been informed by Ziegler of the nature of his original HDPE catalyst used it to polymerize propylene and obtained a partially crystalline essentially isolaclic polypropylene more on this shortly Subsequently Natta and his coworkers made changes to the catalyst replacing TiCl4 with TiCl3 which increased the isotacticity of polypropylene from 5070 to 8090 Into Court Natta s research in this area was funded by the Italian company Montecatini and a patent was led jointly soon thereafter Unfortunately this caused considerable bad blood between Ziegler and Natta and resulted in one of the longest lasting patent cases of all time he Many Uses 0 39 Polypropylene Summary 1950 1953 ZieglerNatta Catalysts Metal Oxide Catalysts Lin ear PE and stereoregular polyole ns Coordination Polymerization X Resl igll ic z 6H u u Catalyst 039 i CH2 9H X Isomerism in Polymers Sequence isomerism 395Ter39eoisomer39ism in vinyl polymers 395Tr39ucTur39al isomerism in diene polymers Two molecules are said to be isomers if th ey are made up of the same number and types of atoms but differ in the arrangement of th ese atoms Stereoisomerism in Vinyl Polymers Polymeriza rion of a Vinyl monomer CH2 CHX where amThing excep r hydrogen lea s o polymers wiT micros rruc rures Tha r are described in Terms of Tadicify Mesa Diad Racemic Diad Isotactic Chains Part of an isoiuciic polypropylene chain seen from the side The same chain seen more from the top Syndiotactic Chains Here are Two more polypropylene chains bo ih shown as if we were looking down from on Topquot One of These consists of Llnl l39S That are all racemic To one anoTher and is called syndiofac c The oTher has a random arrangement of Llnl l39S and we call such chains aTacT c Which one is The a iac iic chain A a A Tacticity in Some Commercially Important Polymers Polys ryrene a rac ric Polypropylene largely iso rac ric PVC largely a rac ric Some syndiofacfic sequences 9 PMMA a rac ric