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Hydrocarbon Molecules

Hydrocarbon Molecules. Unsaturated: Double and triple bonds C n H 2n C n H 2n-2 eg., Ethylene Acethylene CH 2 =CH 2 CH  CH C 2 H 4 C 2 H 2. Hydrocarbon Molecules. Saturated: single bonds eg., CH 4 ,C 2 H 6 , C 3 H 8 C n H 2n+2

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Hydrocarbon Molecules

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  1. Hydrocarbon Molecules Unsaturated: Double and triple bonds CnH2n CnH2n-2 eg., Ethylene Acethylene CH2=CH2 CHCH C2H4 C2H2 Chapter 14: Polymer Structures

  2. Hydrocarbon Molecules Saturated: single bonds eg., CH4,C2H6, C3H8 CnH2n+2 Isomerism: n-butane Isobutane Straight chain Branched chain Chapter 14: Polymer Structures

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

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

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

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

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

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

  9. 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 Chapter 14: Polymer Structures

  10. Molecular weight continue… Number average molecular weight, =xiMi Where Mi=Mean molecular weight within a size range xi=Fraction of number of chains within the corresponding (same) size range Chapter 14: Polymer Structures

  11. Molecular weight continue… Weight Average Molecular weight, =wiMi Where, Mi=Mean molecular weight within a size range wi=weight fraction of molecules within the same size range Chapter 14: Polymer Structures

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

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

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

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

  16. 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. Chapter 14: Polymer Structures

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

  18. Problem 14.1: continue… xiMi=23,200 Where, : weight average molecular weight Chapter 14: Polymer Structures

  19. Problem 14.1: continue… PVC: C2H3Cl Chapter 14: Polymer Structures

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

  21. 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 Chapter 14: Polymer Structures

  22. 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 Chapter 14: Polymer Structures

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  38. Polymer Crystallinity Crystallinity: Packing of chains to produce ordered atomic array. Chapter 14: Polymer Structures

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

  40. Polymer Crystallinity continue… • 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 Chapter 14: Polymer Structures

  41. Polymer Crystallinity continue… • 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 Chapter 14: Polymer Structures

  42. 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 Chapter 14: Polymer Structures

  43. Polymer crystals Fringed micelle model • Aligned small crystalline regions (crystallites or micelles) • Amorphous regions in-between platelets of crystals (10-20 nm thick) (10m long) Chapter 14: Polymer Structures

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

  45. Polymer crystals continue… Spherulitemodel • 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 Chapter 14: Polymer Structures

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

  47. Polymers: summary continue… • Isomerism • Isotactic • Syndiotactic • Atactic • Crystallinity: Degree of crystallinity • Polymer crystals Chapter 14: Polymer Structures

  48. Thermosetting and Thermoplastic Polymers Determined by mechanical behavior upon heating to high temperatures Chapter 14: Polymer Structures

  49. Thermosetting and Thermoplastic Polymers continue… Chapter 14: Polymer Structures

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