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Tacticity of a linear polymer chain

Tacticity of a linear polymer chain. trans conformation. . . .breakage of covalent bonds required to change configuration/tacticity. Isotactic: -R groups on the same side of the C-C plane Syndiotactic: -R groups on alternating side

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Tacticity of a linear polymer chain

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  1. Tacticity of a linear polymer chain trans conformation . . .breakage of covalent bonds required to change configuration/tacticity Isotactic: -R groups on the same side of the C-C plane Syndiotactic: -R groups on alternating side Atactic: -R groups on either side of the C-C plane

  2. Gaseous Liquid Solid “melt”& solutions “glasses” semi-crystalline States of polymers decrease temperature or thermal motion

  3. Polymer melt polymer melt is like a bowl of spaghetti • entanglements limit motion • flows on long-timescales (reptation) • elastic on short-timescales viscoelasticity

  4. Melts ( pure polymer “liquid”) towards crystalline solids . . towards crystalline state • motion frozen on scale of polymer • segmental motion persists

  5. … to semi-crystalline melts crystalline/amorphous lamellae • depends upon cooling rate • backbone/sidegroup structure • tacticity 100-200 Å, 40-80 PE monomers spherulite

  6. Some polymers do . . Some don’t (crystallise) Crystallisation is facilitated by • “regular” or ordered backbone structure, • favorable interchain interactions • lower molecular weight Inter-chain hydrogen bonding favors formation of semi-crystalline regions nylon-6,6 Atactic polystyrene ?

  7. “glasses” . . .intermediate between amorphous melts and possible semi-crystalline states. . . “frozen” structure precedes crystallisation, if it happens; melt conditions glass transition cyrstallisation Tg Tm small scale molecular motions • limited backbone motion • rotations, “crankshaft” • vibrations • flips, wags of side groups

  8. Q4: Using complete sentences, and schematics if helpful, contrast the chain motion of a melt of atactic polypropylene under (a) slow temperature quench; (b) quick temperature quench Q5: Complete Q4 again, starting from a melt of nylon6,6

  9. Q6: Atactic-polyvinylchloride (PVC) is amorphous, whereas syndiotactic-PVC is partially cyrstalline. But atactic- polyvinylalcohol is partly crystalline. Why? Q7: Do you predict the Tm of nylon-6,6 to be higher or lower than that of polyethylene? Why?

  10. Polymer solutions “dilute”, semi-dilute, through to concentrated Rheology: a study of the flow of polymer melts and solutions (shear-thinning, die swell, energy requirements for mold filling, design of mixers, extruders

  11. Block copolymer solutions and melts: making patterned surfaces and ordered melt morphologies

  12. Scientists, academics < 1930s Industrialists • 1830 Charles Goodyear,: vulcanised • rubber • Hevea brasiliensis + D + S • elastomeric material • 1847 Christian Schonbern • Cellulose + nitric acid • cellulose nitrate • 1860 Leo Baekeland (Bakelite) • phenol-formaldehyde resin • 1930s DuPont (USA) nylon, teflon • Dow (USA) polystyrene • 1939 ICI (UK) LDPE • WWII: shortage of natural rubber! “A damned gooey mess” Another failed synthesis

  13. Scientists begin to look at complex systems . . . . 1920’s Hermann Staudinger, German Physical Chemist “long-chained molecules or macromolecules” interacting, separate very long, alkane-like intermediate species but misunderstood . e.g., Tm, flow behaviour flexibility

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