Polymer Chemistry
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Polymer Chemistry Basic Principles and Introduction Prof. Y.M. Lee School of Chemical Engineering, College of Engineering Hanyang University Spring 2004 WeWe livelive inin aa polymerpolymer age!!age!! RubberRubber Elastomers PlasticsPlastics Elastomers FibersFibers CoatingsCoatings ProteinProtein CelluloseCellulose AdhesivesAdhesives Spring 2004 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” 1) Addition Polymerization Ethylene H C CH 2 2 * CH2 CH2 n * CH CH Styrene H2C CH * 2 n * Spring 2004 2) Condensation Polymerization -H O 2 Ethylene glycol OCH CH HOCH2CH2OH * 2 2 n * 4-Hydroxymethyl HOCH CO H benzoic acid 2 2 O -H2O * O CH2 C n * Spring 2004 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. O O * * n * * n O Spring 2004 Historical Milestones in Polymer Science •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. Spring 2004 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. Spring 2004 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 Spring 2004 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. Spring 2004 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! Spring 2004 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) Spring 2004 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 n CH C H2C CH * n -2-2* Vinyl acetate O O (a important industrial C O C O monomer) CH3 CH3 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). Spring 2004 Definitions Homopolymer: -A-A-A-A-A-A-A-A-A- Copolymer: (1) Alternating copolymer: -A-B-A-B-A-B-A-B-A-B-A-B- (2) Random copolymer: -A-A-B-A-B-B-A-B- (3) Block copolymer: -A-A-A-A-A-A-B-B-B-B-B-B- (4) Graft copolymer: -A-A-A-A-A-A-A-A-A-A-A-A- B B-B-B-B-B-B-B- Spring 2004 Representation of polymer types (a) Linear (b) Branched (c) Network (a) Star (b) Comb (c) Ladder (d) Semiladder Spring 2004 Network Polymers (Crosslinked polymers) Network polymers arise when polymer chains are linked together or when polyfunctional instead of difunctional monomers are used. Ex) Vulcanized rubber 1. Excellent dimensional stability Polymer crosslink 2. X-polymers will not melt or flow and cannot be molded. Chains (thermosetting or thermoset ÅÆ thermoplastic) 3. Usually insoluble, only swelling Spring 2004 Polymerization processes (traditional) 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 Spring 2004 3. Polyurethane from diisocyanate and diol 4. Hydrocarbon polymer from ethylene and α,ω-dibromide by the Wurtz reaction Spring 2004 Polymerization processes (recent) 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 AB * ABn * Reactive functional group in one molecule AA+ BB Two difunctional monomers * A A B B n * Ex) Polyesterification Å diol + dibasic acid or intermolecularly between hydroxy acid molecules Spring 2004 Carothers’ equation 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 No − N p = or N = No (1− p) No N 1 o = DP = N 1− p Ex) At 98% conversion, p = 0.98 Æ DP = 50 Spring 2004 2. Chain-reaction polymerization Chain-reaction polymerization involves two distinct kinetic steps, initiation and propagation. Initiation . R . + H2C CH2 RCH2CH2 Propagation . RCH CH CH CH . RCH2CH2 + H2C CH2 2 2 2 2 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. Spring 2004 3. Comparison of step-reaction and chain-reaction polymerization Step reaction Chain reaction Growth occurs throughout matrix by reaction Growth occurs by successive addition of monomer between monomers, oligomers, and polymers units to limited number of growing chains DP low to moderate DP can be very high Monomer consumed rapidly while molecular Monomer consumed relatively slowly, but molecular weight increases slowly weight increases rapidly No initiator needed; same reaction mechanism Initiation and propagation mechanisms different throughout No termination step; end groups still reactive Usually chain-terminating step involved Polymerization rate decreases steadily as Polymerization rate increases initially as initiator units functional groups consumed generated; remains relatively constant until monomer depleted Spring 2004 Nomenclatures Vinyl polymers Spring 2004 Nonvinyl polymers Spring 2004 Nonvinyl polymers Spring 2004 Industiral polymers Plastics Commodity plastics Spring 2004 Engineering plastics Spring 2004 Thermosetting plastics Spring 2004 Fibers Synthetic fibers Spring 2004 Rubber (elastomers) Synthetic rubber Spring 2004 Chap 3. Bonding in Polymers Primary Covalent Bond C C C H H δδ_ + O C O H N Hydrogen Bond δ _ H O δ + δ_ Dipole Interaction C N N C δ+ CO Ionic Bond O +1 _ Zn O CO Van der Waals CH2 CH2 Spring 2004 PE γm r Attraction Repulsion Spring 2004 Chap 4. Stereoisomerism Activity (Tacticity) CH3 CH3 Atactic C C C C C C C C C CH3 CH3 CH3 Isotactic C C C C C C C C C CH3 CH3 CH3 CH3 CH3 CH3 Syndiotactic