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Dane Holte Baran Group Meeting Nov. 12, 2011 Polymer Chemistry Baran Group Meeting Polymer Chemistry Nov. 12, 2011 Dane Holte A polymer is a large molecule composed of repeating structural units. A Brief Historical Background: According to IUPAC, "Conventionally, the word polymer used as a noun is The work of H. Braconnot in 1777 and C. Schönbein 1846 leads to the ambiguous; it is commonly employed to refer to both polymer substances and discovery of nitrocellulose, which can be used to produce celluloid. polymer molecules. Henceforth, macromolecule is used for individual molecules and polymer is used to denote a substance composed of OH macromolecules. OH O HO O HO O O —A—A—A—A—A—A—A—A– Homopolymer OH HNO —A—B—B—A—B—A—A—B– Random copolymer OH 3 —A—B—A—B—A—B—A—B– Alternating copolymer Cellulose —A—A—A—A—B—B—B—B– Block copolymer —A—A—A—A—A—A—A—A– Graft copolymer Me Me "Camphored nitrocellulose" ONO2 B—B—B—B—B—B– (Celluloid, or Pyroxylin, or Xyloidine, or Xylonite, or ...) ONO2 Me O O2NO Used in billiard balls, guitar O O O NO O O picks, and ping pong balls. KI, EtOH 2 ONO 2 ONO2 Celluloid was the first industrial thermoplastic, a polymer which liquifies Nitrocellulose, or "guncotton" upon heating and solidifies to a glassy Used in firearms, nitrate film base, state upon cooling. Often thermoplastics are high-molecular-weight and chains Western blots, and AFM (due to associate through Van der Waals forces nonspecific affinity for amino acids) Ladder polymer (PE), H-bonding (nylon), or pi-stacking (PS). Star polymer Polycatenane In 1834, F. Ludersdorf and N. Hayworth discover that adding sulfer to natural rubber decreases the stickiness. In 1844, C. Goodyear gets the U.S. patent. Me Me S S Me S S Me sulfur S S Me Me S Me Me S ! + S (S)n Comb polymer Dendrimer Me Me Me Me Me Me Me Me cis-1,4-polyisoprene Vulcanized rubber Used as early as 1600 B.C., both Used in a vast array of products from synthetic and natural rubber are in tires to bowling balls, the properties use today. Of the 21 million tons are dependent on type and amount produced in 2005, 42% was natural. of crosslinker. Polyrotaxane Natural rubber is a thermoplastic and an Thermosetting plastic , a elastomer, or rubber, a polymer which polymer that irreversibly cures, is both viscous and elastic, exhibiting the or hardens, through either heat, Network Polymer ability to stretch and retract. chemical reaction, or irradiation. Baran Group Meeting Polymer Chemistry Nov. 12, 2011 Dane Holte Phenol–formaldehyde condensation polymers: "Discovery" of polymers: L. Baekeland invents the first totally synthetic plastic in 1907, Bakelite. H. Staudinger proposed in 1920 that previously measured molecular weights + OH CH2O, H OH OH of rubber were a result of extremely large molecules, made up of smaller subunits linked together by covalent bonds. This was contrary to the !, pressure prevailing opinion that the observed high molecular weights were a result of aggrigation of small molecules into colloids. C6H6O>CH2O base, ! OH C H O<CH O “It is not improbable,” Staudinger commented, “that sooner or later a way will 6 6 2 be discovered to prepare artificial fibers from synthetic high-molecular products, because the strength and elasticity of natural fibers depend OH OH OH OH exclusively on their macro-molecular structure – i.e., on their long thread- HO OH shaped molecules.” Trans. Faraday Soc. 1936, 32, 323– 335. Staudinger received the 1953 Nobel Prize in Chemistry for “his discoveries in OH the field of macromolecular chemistry.” HO HO OH Low molecular weight novolacs are Cationic polymerization: the initially formed prepolymers, First developed by BASF in 1931, butyl rubber is the one of the few (only?) OH which can be cured in a second step commercial rubber prepared by cationic polymerization. by the addition of more formaldehyde. Me Me Lewis acid Me HO + Me Me Me Me Low molecular weight resoles are the Me –100 ºC initially formed prepolymers, which IB:IP, 97:3 chlorinated solvent n undergo further polymerization in a second heating, or acid catalyzed step for form resites, containing ethers, quinone methide cycloadducts, and additional methlene linkages. A condensation polymer is any polymer formed through a condensation reaction, simultainiously releasing a small molecule (e.g. H2O or MeOH). This is opposed to an additon polymer , which contains all the original atoms of the monomer from which it arose. Wallace Carothers: Harvard (1926–1927) then DuPont (1928–1937) In 1930, he invents polycloroprene (Neoprene): In 1930, he invents the first polyester. In 1931, he was known to keep a capsule of KCN on his watch chain. In 1935, he Cl invents the first nylon: O H 1937, "he felt that he had N not accomplished much and had run out of ideas." In 1937, he commits suicide taking KCN in lemon juice, knowing that the acidic solution would increase the speed of the poison. Baran Group Meeting Polymer Chemistry Nov. 12, 2011 Dane Holte Anionic polymerization: !NiMi Number average molecular weight: Mn = Cyanoacrylate adhesive (super glue): !Ni Developed in 1942 by Kodak. 2 !WiMi !NiMi Weight average molecular weight: Mw = = inert bottle !wi !NiMi N N N Polydispersity index: Mw NC CO Me apply to surface 2 Mn + Measurement of number average molecular weight (M ): O atmospheric H2O HO O O n n MeO MeO MeO End-group analysis (< 50,000 Da; generally only for linear polymers) H2O Membrane osmometry (50,000–2,000,000 Da, widely used) Freezing-point depression (< 40,000 Da, preferred < 20,000 Da) Living polymerization is a form of addition polymerization in which the ability of the growing Boiling-point elevation (< 40,000 Da, preferred < 20,000 Da) polymer chain to terminate has been removed. Often growing at a more constant rate, the PDI can be lower Vapor pressure osmometry (< 25,000 Da) and the chain length more predictable. Mass spectrometry (tens of thousands achievable with poor resolution, for Living anionic polymerization: monodisperse biopolymers, up to 400,000 Da possible) First demonstrated by M. Szwarc in 1956. Refractive Index Measurements ("low" molecular weight polymers) 0 + + Na Na + polystyrene Measurement of weight average molecular weight (Mw): NH3 Light scattering (10,000–10,000,000 Da) Na-naphthanlene: Ultracetrifugation (particularly useful for proteins, $) bright green Viscometry (simple, widely used) cat. dimerize Measurement of molecular weight distribution: + Na Gel permeation (size exclusion) chromatography THF Ph Ph Fractional solution anionic Fractional precipitation polymerization Thin-layer chromatography Me highly cis- Me Methods of analysis: n "t IR Ph Ph AFM Me "living" polymer Raman Secondary–ion mass spectrometry NMR Ph bright red Several types of thermal analysis EPR Several types of mechanical analysis PI–PS–PI block copolymer O 2 H O UV–Vis Chemical resistance 2 Electrical properties Ph Fluorescense X-ray, electron, and neuron scattering O2 + SEM Ph Ph Ph Ph Photoacoustic colorless, significant colorless, no Electron Spectroscopy for Chemical Analysis increase in viscosity Nature, 1956, 178, 1168–1169. change in viscosity Baran Group Meeting Polymer Chemistry Nov. 12, 2011 Dane Holte minimize Free Radical Polymerization: steric clash H H Chain-reaction polymerization, polymerization P involving initiation followed by propagation. As P Initiation such, the monomer is consumed relatively slowly Zr P Zr Zr and average molecular weights can be very high. H H Me H Me CH2 R + R CH2 H H H H2C minimize steric clash, maximize Propagation distance of polymer from catalyst CH R CH2 + 2 R CH2 H2C H H Ok for polyethylene, but what about polypropylene? H H H H P Me Me P P Initiation Zr Zr Zr Me Me R CH H H Me R + Me H2C Me Ziegler-Natta Catalysts : Originally Ti-based catalysts used for the polymerization of terminal olefins; Propagation awarded the Nobel Prize in chemistry in 1963. Today, this class of catalysts has been expanded to include: 1. Solid supported Ti-based catalysts, often used in conjunction with organoaluminum cocatalysts R CH + R CH R CH 2. Metallocene catalysts, often of Ti, Zr, or Hf, and typically in conjuntion with MAO H C Me 3. Post-metallocene catalysts, various transition metals used with multidentate N and O based ligands, often Me 2 Me Me Me Me Me use MAO Angew. Chem. Int. Ed. 1985, 24, 507–508. J. Am. Chem. Soc. 1994, 116, 2988–2995. Me Cl Me Me Me Me Me Me Me Me Me Zr Isotactic: substituents located on the same side of the molecule; helical Cl strucure; crystalline Me MAO Me Me Me Me Me Me Me Me ...or Me Me Me Me Me Me Me Me 98% sydiotactic, 2% isotactic, little–no% atactic Atactic: random arrangement of substituents; amorphous oil/wax Me Me ...or P P P Me Me Me Me Me Me Me Me Zr Zr Zr Syndiotactic: alternating substituents; granular particles Atactic polymers simply made by free radical polymerization (see above). Me Me But what bout isotactic? Syndiotactic? Enantiopure? rac Cl Zr Cl Me Me Me Me P Zr P Zr Me MAO Me Me Me Me Me Me Me Me Me MAO = methylaluminoxane, (Al(CH3)O)n J. Am. Chem. Soc. 1988, 110, 6255–6256. 95% isotactic, 3.2% atactic, 0.9% sydiotactic Chem G8310: Asymmetric Catalysis, Class Notes, J. Leighton, Columbia Univ. 2007 Baran Group Meeting Polymer Chemistry Nov. 12, 2011 Dane Holte Nitroxide Mediated Living Radical Polymerizations (NMP, ~1994): Atom Transfer Radical Polymerization (ATRP, 1995): General Mechanism X–X General Mechanism Initiation Z Z coupling kact R–X + Mn / Lig R + Mn+1 / Lig X + R k X–R deact X monomer monomer Propagation Z Z kact P–X + Mn / Lig P + Mn+1 / Lig X–M–R X–M + R kdeact X kt A Specific Example kp Me Me monomer O O Termination TEMPO O Ph + O N Ph O Ph O A Specific Example 80 ºC O Ph Me Me excess 42 % Me stable to air, light, moisture, and heat (<100 ºC) CuBr, 110 ºC Br + polystyrene Me Me 4 h Me Me 79% conv.
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