PC chap1 5

Information about PC chap1 5

Published on October 16, 2007

Author: Marigold

Source: authorstream.com

Content

Slide1:  Basic Principles and Introduction Prof. Y.M. Lee School of Chemical Engineering, College of Engineering Hanyang University Polymer Chemistry Slide2:  We live in a polymer age!! Plastics Fibers Elastomers Coatings Adhesives Rubber Protein Cellulose Slide3:  Polymer: large molecules made up of simple repeating units Greek poly, meaning many, and mer, meaning part Synonymous Term: Macromolecules Synthesis of Polymer: Synthesized from simple molecules called “monomers” Ethylene Styrene 1) Addition Polymerization Slide4:  2) Condensation Polymerization -H2O Ethylene glycol 4-Hydroxymethyl benzoic acid -H2O Slide5:  Historical Milestones in Polymer Science Prehistory – 19th Century Mankind relies on natural polymeric materials like wood, bone, and fur. 1833 Polymer was first used by the Swedish chemist Berzelius. 1839 Charles Goodyear vulcanizes natural rubber with sulfur, launches rubber industry. The polymerization of styrene was firstly reported. 1860s Poly(ethylene glycol) and poly(ethylene succinate) was published. Slide6:  1870 John Wesley Hyatt invents Celluloid through chemical treatment of natural cellulose (nitrated cellulose). 1887 Count Hilaire deChardonnet spins cellulose nitrate into Chardonnet silk 1909 American inventor Leo Baekeland (who had already earned considerable success with his light-sensitive photographic paper) treated phenol with formaldehyde to produce Bakelite, the first successful fully synthetic polymer material. Historical Milestones in Polymer Science Slide7:  Historical Milestones in Polymer Science 1920 German chemist Hermann Staudinger proposes his Macromolecular Hypothesis, claims giant molecules exist (revealing view is that plastics are assemblies of small molecules). Staudinger is widely criticized but eventually becomes the first polymer chemist to win the Nobel Prize in Chemistry (in 1953). 1928 German chemists Kurt Meyer and Herman Mark confirm the existence of macromolecules through x-ray studies. Slide8:  Historical Milestones in Polymer Science 1928 DuPont hires Professor Wallace Hume Carothers from Harvard to start first basic R&D lab in the USA. 1930s - An explosion of new materials. Wallace Carothers - Polyamide (Nylon) Polychloroprene (Neoprene) Waldo Semon - Polyvinyl chloride (PVC) Roy Plunket - Polytetrafluoroethylene (Teflon) Paul Flory - Theory of gelation 1940s WWII leads to synthetic rubber program Professor Peter Debye develops light scattering for MW measurement Flory and Huggins develop theory of polymer thermodynamics Slide9:  Historical Milestones in Polymer Science 1953 German chemist Karl Ziegler and Italian chemist Giulio Natta develop effective catalysts for olefin polymerization allowing large scale production of polyethylene and polypropylene. They receive the Nobel Prize in 1963. 1974 Professor Paul Flory is awarded the Nobel Prize in Chemistry for his many contributions to polymer science. 1986 Chemical Engineering Professor Robert Langer and Medical Doctor Joseph Vacanti demonstrate the use of polymers in tissue engineering. Liver cells grown on a special polymer can be transplanted and still function. Slide10:  Historical Milestones in Polymer Science 2000 The Nobel Prize in Chemistry is given “for the discovery and development of electrically conductive polymers.” Professor Alan J. Heeger at the University of California at Santa Barbara, USA Professor Alan G. MacDiarmid at the University of Pennsylvania, USA Professor Hideki Shirakawa at the University of Tsukuba, Japan Polymer Science and Technology remains a vital and exciting field! Slide11:  Important Advances in Polymer Science High thermal and oxidation-stable polymer: high performance aerospace applications Engineering plastics – polymers designed to replace metals High strength aromatic fibers – a variety of applications from tire cord to cables for anchoring oceanic oil-drilling platforms Non flammable polymers – emit a minimum of smoke or toxic fumes Degradable polymers – allow controlled release of drugs or agricultural chemicals Polymer for a broad spectrum of medical applications – from degradable sutures to artificial organs Conducting polymers – exhibit electrical conductivities comparable to those of metals Polymer that serve as insoluble support for catalysts or for automated protein or nucleic acid synthesis (Bruce Merrifield, who originated solid-phase protein synthesis, was awarded the Nobel Prize in Chemistry in 1984) Slide12:  Chap 2. Types of Polymers & Definitions Polymer: a large molecule whose structures depends on the monomer or monomers used in preparation Oligomer: low-molecular weight polymer (a few monomer units) Repeating unit (RU): monomeric units (examples: polyethylene) Degree of polymerization (DP): the total number of structural units, including end groups. It is related to both chain length and molecular weight Vinyl acetate (a important industrial monomer) n If DP (n) = 500, for example, M.W.= 500 × 86(m.w. of structural unit) = 43,000 Because polymer chains within a given polymer sample are almost always of varying lengths (except for certain natural polymers like proteins), we normally refer to the average degree of Polymerization (DP). - 2 Slide13:  Definitions Slide14:  (a) Linear (b) Branched (c) Network (a) Star (b) Comb (c) Ladder (d) Semiladder Representation of polymer types Slide15:  Network polymers arise when polymer chains are linked together or when polyfunctional instead of difunctional monomers are used. Ex) Vulcanized rubber Polymer Chains crosslink Excellent dimensional stability X-polymers will not melt or flow and cannot be molded. (thermosetting or thermoset  thermoplastic) 3. Usually insoluble, only swelling Network Polymers (Crosslinked polymers) Slide16:  Traditionally, polymers have been classified into two main groups: 1) addition polymers and 2) condensation polymers (first proposed by Carothers) 1. Polyester from lactone and ω-hydroxycarboxylic acid: 2. Polyamide from lactam and ω-amino acid Polymerization processes (traditional) Slide17:  3. Polyurethane from diisocyanate and diol 4. Hydrocarbon polymer from ethylene and ,ω-dibromide by the Wurtz reaction Slide18:  In more recent years the emphasis has changed to classifying polymers according to whether the polymerization occurs in a stepwise fashion (step reaction or step growth) or by propagating from a growing chain (chain reaction or chain growth). 1. Step reaction polymerization Reactive functional group in one molecule Two difunctional monomers Ex) Polyesterification  diol + dibasic acid or intermolecularly between hydroxy acid molecules Polymerization processes (recent) Slide19:  If one assumes that there are No molecules initially and N molecules (total) after a given reaction period, then amount reacted is No-N. The reaction conversion, p, is then given by the expression or Carothers’ equation Slide20:  2. Chain-reaction polymerization Chain-reaction polymerization involves two distinct kinetic steps, initiation and propagation. Initiation Propagation + . + . In both addition and ring-opening polymerization, the reaction propagates at a reactive chain end and continues until a termination reaction renders the chain end inactive (e.g., combination of radicals), or until monomer is completely consumed. Slide21:  3. Comparison of step-reaction and chain-reaction polymerization Step reaction Growth occurs throughout matrix by reaction between monomers, oligomers, and polymers DP low to moderate Monomer consumed rapidly while molecular weight increases slowly No initiator needed; same reaction mechanism throughout No termination step; end groups still reactive Polymerization rate decreases steadily as functional groups consumed Chain reaction Growth occurs by successive addition of monomer units to limited number of growing chains DP can be very high Monomer consumed relatively slowly, but molecular weight increases rapidly Initiation and propagation mechanisms different Usually chain-terminating step involved Polymerization rate increases initially as initiator units generated; remains relatively constant until monomer depleted Slide22:  Vinyl polymers Nomenclatures Slide23:  Nonvinyl polymers Slide24:  Nonvinyl polymers Slide25:  Plastics Commodity plastics Industiral polymers Slide26:  Engineering plastics Slide27:  Thermosetting plastics Slide28:  Fibers Synthetic fibers Slide29:  Synthetic rubber Rubber (elastomers) Slide30:  Chap 3. Bonding in Polymers Primary Covalent Bond C C C H Hydrogen Bond O H H O C O H N d d + d d + Dipole Interaction C N N C d d + Ionic Bond C O O Zn O C O +1 _ _ _ _ Van der Waals CH 2 CH 2 Slide31:  PE m r Attraction Repulsion Slide32:  Chap 4. Stereoisomerism Activity (Tacticity) Atactic C CH 3 C C C C C C C C C C C C C C C C C C C C C C C C C C CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 Isotactic Syndiotactic CH 3 CH 3 CH 3 Slide33:  Unit cell Six crystal system  Isometric; 3 mutually perpendicular axes of equal length.  Tetragonal; 3 perpendicular axes are equal in length.  Orthogonal; 3 perpendicular all of different length.  Monoclinic; 3 axes of unequal length. 2 are not  to each other both are  to the third  Triclinic; all 3 axes of different length.  Hexagonal; 4 axes, 3axes in the same plane & symmetrically spa and of equal length. Chap 5. Crystallinity Slide34:  Polyethylene: a = 7.41Å , b = 4.94Å , c = 2.54Å Chain axes Unit cell volume = a×b×c = 93.3 Å3 Mass in cell corner = 8 CH2’s shared / 8 cells = 1 CH2 2 sidewall CH2’s = 2/2 = 1 CH2 Top & bottom face CH2’s = Slide35:  결정화의 조건 정규 결정 격자로 사슬이 packing 되려면 ordered, regular chain structure가 필요. 따라서 stereoregular structure 를 가진 고분자가 irregular structure 를 가진 고분자보다 결정화가 될 확률이 높다. 결정격자간 2차 간력이 강해서 열에너지에 의한 무질서 효과(엔트로피 효과)를 극복할 수 있어야 함. biaxial stress(stretching) is stronger than uniaxial stretch ∵different arrangement of chain. Slide36:  Crystallizability 고분자의 화학구조에 의한 고유의 성질  구조의 규칙성  강한 친화력 Crystallinity 가공 history 에 직접 의존  Temperature/time  Stress/time Slide37:  몇가지 결정 MODELS Fringed-Micelle Model fringed-micelle(or crystallites) 가 amorphous matrix 내에 퍼져 있음 orientation Slide38:  2. Folded-Chain Crystallites 희박용액으로부터 single crystal 이 성장하여 polymer crystal 이 생성됨을 발견. 냉각 또는 solvent 가 evaporation함으로서 thin, pyramidal, or platelike polymer crystal(lamellae)가 생성. 이 결정들은 두께 약 100Å에 수십만 Å 길이를 가짐. X-ray 결과로는 chain axis가 flat surface에 수직으로 배열 됨이 알려짐. 또한 각자 사슬들이 1000Å 이상의 길이를 가짐. 따라서 chain이 folded back and forth 할 수 밖에 없다는 결론. Dilute solution으로부터 뿐 아니라 melt로부터도 이 같은 lamellae 형성 model이 적용됨. Slide39:  3. Extended-Chain X-tal melt 상태에서 extension(stress)을 가하면서 결정화가 일어날 때 확장하는 방향으로 사슬이 배열하며 fibrillar 구조를 형성. 이들은 extended-chain crystals로 알려져 있고 이들은 먼저 서로 평행으로 배열되어 있고 chain folding은 minimum. “Shish-Kebab” “Shish-Kebab” Slide40:  4. Spherulites 고분자 사슬들은 crystallites를 형성할 수 있도록 배열되어 있으며 이들 crystallites들은 spherulites라고 하는 커다란 집합체로 되어 있다. 이들 spherulites는 핵형성점 으로부터 원형으로 성장. 따라서 각개 spherulites는 존재하는 핵의 숫자로부터 조절될 수 있으며 핵이 더 있으면 더 많은 작은 spherulites가 됨. Spherulites가 큰 것들은 고분자의 brittleness . Brittleness를 적게 하려면 nucleating agent를 첨가하든가 고분자를 shock cooling 함. Slide42:  Specific volume

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