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

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

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

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

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

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

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

11. 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

12. 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

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

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

15. 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

16. 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

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.
Chapter 14: Polymer Structures

18. 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

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

20. Problem 14.1: continue… PVC: C2H3Cl C H Cl Atomic weight (g/mol) 12.01
1.01
35.45
Chapter 14: Polymer Structures

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

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

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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

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

33. 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

34. 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

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

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

37. 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

38. 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

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

41. 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

42. 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

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
Chapter 14: Polymer Structures

44. 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

45. 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

46. Polymer crystals continue…
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
Chapter 14: Polymer Structures

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

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

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

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

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

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