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1. Chapter 14: Polymer Structures 2 Hydrocarbon Molecules Unsaturated: Double and triple bonds C n H 2n C n H 2n-2 eg., EthyleneAcethylene CH 2 =CH 2.

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Presentation on theme: "1. Chapter 14: Polymer Structures 2 Hydrocarbon Molecules Unsaturated: Double and triple bonds C n H 2n C n H 2n-2 eg., EthyleneAcethylene CH 2 =CH 2."— Presentation transcript:

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2 Chapter 14: Polymer Structures 2 Hydrocarbon Molecules Unsaturated: Double and triple bonds C n H 2n C n H 2n-2 eg., EthyleneAcethylene CH 2 =CH 2 CH  CH C 2 H 4 C 2 H 2

3 Chapter 14: Polymer Structures 3 Saturated: single bonds eg., CH 4,C 2 H 6, C 3 H 8 C n H 2n+2 Isomerism: n-butane Isobutane Straight chainBranched chain Hydrocarbon Molecules

4 Chapter 14: Polymer Structures 4 Source: William Callister 7 th edition, chapter 14, page 493, table 14.2 Hydrocarbon Molecules R-COOH R-CHO 5 6 HR-C

5 Chapter 14: Polymer Structures 5 Gigantic: Macromolecules Monomer: One unit Polymer Many units eg., one unit Polymer Molecules

6 Chapter 14: Polymer Structures 6 PTFE: TEFLON Polytetrafluoro ethylene Mer Polymer Molecules continue…

7 Chapter 14: Polymer Structures 7 Polymer Molecules continue… PVC: Vinyl Polyvinyl chloride Polypropylene: Mer

8 Chapter 14: Polymer Structures 8 Polymer molecules Homopolymer:Repeating units of the chain are of the same type Co-polymer: Two or more different mer units.

9 Chapter 14: Polymer Structures 9 Polymer molecules continue Bifunctional: Two (2) active bonds Trifunctional: Three (3) active bonds

10 Chapter 14: Polymer Structures 10 Molecular weight Large macromolecules synthesized from molecules Not all polymer chains grow to the same length Average molecular weight is determined by measuring viscosity and osmotic pressure The chain is divided into size ranges No. of moles (or fraction) of each size range is determined

11 Chapter 14: Polymer Structures 11 Molecular weight continue… Number average molecular weight, =  x i M i Where M i =Mean molecular weight within a size range x i =Fraction of number of chains within the corresponding (same) size range

12 Chapter 14: Polymer Structures 12 Molecular weight continue… Weight Average Molecular weight,=  w i M i Where, M i =Mean molecular weight within a size range w i =weight fraction of molecules within the same size range

13 Chapter 14: Polymer Structures 13 Molecular weight continue… Source: William Callister 7 th edition, chapter 14, page 498, figure 14.3 Notice the shift

14 Chapter 14: Polymer Structures 14 Source: William Callister 7 th edition, chapter 14, page 498, figure 14.4 Molecular weight continue…

15 Chapter 14: Polymer Structures 15 Molecular weight continue… Degree of polymerization (n): n= Average no of mer units in a chain n n =Number average degree of polymerization n w =Weight average degree of polymerization Mer molecular weight

16 Chapter 14: Polymer Structures 16 Molecular weight continue… For a copolymer (i.e., two or more mer units), Where, f j = chain fraction of mer m j =molecular weight of mer

17 Chapter 14: Polymer Structures 17 Problem 14.1: Computations of Average Molecular Weights and Degree of Polymerization Assume that the molecular weight distributions shown in Figure 14.3 are for poly(vinyl chloride). For this material, compute: (a) the number-average molecular weight, (b) the degree of polymerization, and (c) the weight-average molecular weight.

18 Chapter 14: Polymer Structures 18  x i M i =21,150 Where, x i : Fraction of total no. of chain within the corresponding size change : Number average molecular weight Problem 14.1: continue…

19 Chapter 14: Polymer Structures 19 Problem 14.1: continue…  x i M i =23,200 Where, : weight average molecular weight

20 Chapter 14: Polymer Structures 20 Problem 14.1: continue… PVC: C 2 H 3 Cl CH Cl Atomic weight (g/mol)

21 Chapter 14: Polymer Structures 21 Problem 14.1: continue… Number average degree of polymerization,

22 Chapter 14: Polymer Structures 22 Molecular weight of polymers Melting point increases with molecular weight (for up to 100,000 g/mol). i.e. increased intermolecular forces Long chain  increased bonding between molecules. (Van der Waals or hydrogen bond) At room temperature, Short chains: Molecular weight: 100 g/mol – liquids/gases (1000 g/mol: waxes, soft resins) High polymers: 10,000 to several million g/mol – solids

23 Chapter 14: Polymer Structures 23 Molecular shape Single chain bonds  can rotate like a cone/bend in three dimensions Bends, twists, kinks, in single chain molecules C  C: rigid (rotationally) bulky or large side group: restricted rotation Benzene ring: restricted rotation

24 Chapter 14: Polymer Structures 24 Molecular structure Linear Mer units end-to-end in chains Source: William Callister 7 th edition, chapter 14, page 502, figure 14.7(a) e.g., Polyethylene PVC

25 Chapter 14: Polymer Structures 25 Molecular structure continue…. Polystyrene PMMA Poly(methyl methacrylate)

26 Chapter 14: Polymer Structures 26 Molecular structure continue…. Branched Polymers Side-branch chains Less packing efficiency; lower density Source: William Callister 7 th edition, chapter 14, page 502, figure 14.7 (b)

27 Chapter 14: Polymer Structures 27 Cross-linked Polymers Formed by non-reversible chemical reaction Additives covalently bonded to chains e.g., sulfur in vulcanizing Source: William Callister 7 th edition, chapter 14, page 502, figure 14.7 (c) Molecular structure continue….

28 Chapter 14: Polymer Structures 28 Net-work polymer Three active covalent bonds Highly cross-linked Molecular structure continue…. Source: William Callister 7 th edition, chapter 14, page 502, figure 14.7 (d)

29 Chapter 14: Polymer Structures 29 Molecular configurations Head-to-tail configuration Bonded to alternate carbons on the same side Source: William Callister 7 th edition, chapter 14, page 503 Where, R: Alkyl radical

30 Chapter 14: Polymer Structures 30 Molecular configurations continue…. Head-to-head configuration Bonded to adjacent carbon atoms Source: William Callister 7 th edition, chapter 14, page 503

31 Chapter 14: Polymer Structures 31 Isotactic configuration Stereoisomerism Molecular configurations continue…. R groups are situated on the same side of the chain Source: William Callister 7 th edition, chapter 14, page 504

32 Chapter 14: Polymer Structures 32 Syndiotactic On alternate sides Source: William Callister 7 th edition, chapter 14, page 504 Molecular configurations continue….

33 Chapter 14: Polymer Structures 33 Molecular configurations continue…. Atactic At random position Source: William Callister 7 th edition, chapter 14, page 504 Conversion from to another is only by severing branches and through new reaction

34 Chapter 14: Polymer Structures 34 Geometric Isomerism CIS-Isoprene eg., Natural rubber Attacked by acids/alkalis Molecular configurations continue…. TRANS-Isoprene eg., Gutta Percha Highly resistant to acid/alkalis

35 Chapter 14: Polymer Structures 35 Molecular configurations continue…. Geometric Isomerism continue… TRANS- isoprene e.g., Gutta Percha –Highly resistant to acids/alkalis

36 Chapter 14: Polymer Structures 36 Molecular configurations continue…. Source: William Callister 7 th edition, chapter 14, page 506, figure 14.8

37 Chapter 14: Polymer Structures 37 Copolymers (different types of mers) Random Source: William Callister 7 th edition, chapter 14, page 508, figure 14.9(a) Alternate Source: William Callister 7 th edition, chapter 14, page 508, figure 14.9(b)

38 Chapter 14: Polymer Structures 38 Styrene butadiene rubber (SBR), (Random copolymer): Automobile tires. Nitrile butadiene rubber (NBR), Random copolymer): Gasoline hose Block Source: William Callister 7 th edition, chapter 14, page 508, figure 14.9(c) Copolymers continue…

39 Chapter 14: Polymer Structures 39 Polymer Crystallinity Crystallinity: Packing of chains to produce ordered atomic array. Total Crystalline or noncrystalline Crystalline + noncrystalline

40 Chapter 14: Polymer Structures 40 Polymer Crystallinity continue… Where,  s =Density of specimen  a =Density of totally amorphous polymer  c =Density of perfectly crystalline polymer

41 Chapter 14: Polymer Structures 41 Crystallinity characteristics Degree of crystallinity depends on rate of cooling; need sufficient time to result in ordered configuration. Amorphous (No crystallinity) if chemically complex microstructure. Crystalline if chemically simple polymer. e.g., polyethylene, PTFE, even if rapidly cooled Polymer Crystallinity continue…

42 Chapter 14: Polymer Structures 42 Amorphous if network polymer. Crystalline if linear polymer (no restrictions to prevent chain alignment) Amorphous: Atactic stereoisomer. Crystalline: Isotactic or Syndiotactic stereoisomer Amorphous: If bulky/large side-bonded group. Crystalline: Simple straight chain Polymer Crystallinity continue…

43 Chapter 14: Polymer Structures 43 Polymer Crystallinity continue… Amorphous: Most copolymers (and more irregular/ random mers) Crystalline: Alternating or block polymers Amorphous: Random or graft polymers Crystalline: Strong, more resistant to dissolution by softening by heat

44 Chapter 14: Polymer Structures 44 Polymer crystals Fringed micelle model Aligned small crystalline regions (crystallites or micelles) Amorphous regions in-between platelets of crystals ( nm thick) (  10  m long)

45 Chapter 14: Polymer Structures 45 So, multilayered structure Chain-fold model: amorphous molecular chains within platelets; back and forth Polymer crystals continue… Fringed micelle model continue…

46 Chapter 14: Polymer Structures 46 Spherulite model Bulk polymers solidify as small spheres (Spherulites) Within each such sphere, folded crystallites (lamellae), ~10 nm thick form Adjacent spherulites impinge on each other forming planar boundaries e.g., Polyethylene, Polypropylene, PVC, PTFE, Nylon Polymer crystals continue…

47 Chapter 14: Polymer Structures 47 Large molecules of polymers Mers, homopolymers, copolymers Molecular weight –Number-Average –Weight-Average Polymers: summary

48 Chapter 14: Polymer Structures 48 Isomerism  Isotactic  Syndiotactic  Atactic Polymers: summary continue… Crystallinity: Degree of crystallinity Polymer crystals

49 Chapter 14: Polymer Structures 49 Thermosetting and Thermoplastic Polymers Determined by mechanical behavior upon heating to high temperatures ThermosettingThermoplastic Thermosets Become permanently hard upon heating. Do not soften upon subsequent heating Thermoplasts Soften upon heating; harden upon cooling. It is reversible Fabricated by applying heat and pressure

50 Chapter 14: Polymer Structures 50 ThermosettingThermoplastic Initial Heating: Covalent crosslink form and link adjacent molecular chains. Chains are anchored; no vibrational or rotational chain motions, 10-50% of chain mer units are cross- linked As Temperature is increased Secondary bonds break (due to molecular motion). So when stress is applied, adjacent chains move Thermosetting and Thermoplastic Polymers continue…

51 Chapter 14: Polymer Structures 51 Thermosetting and Thermoplastic Polymers continue… ThermosettingThermoplastic Further heating: Severance (breaking) of crosslink bonds and polymer degradation Irreversible degradation upon further heating: Violent molecular vibrations break primary covalent bonds

52 Chapter 14: Polymer Structures 52 Thermosetting and Thermoplastic Polymers continue… ThermosettingThermoplastic Thermoset polymers are harder, stronger and brittle Better dimensional stability e.g., Cross linked and network polymers  Vulcanized rubbers, epoxies and phenolic and some polyester resins Soft and Ductile Most linear polymers and polymers with branched structures with flexible chains


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