chapter 16: polymers. reading all of ch. 16 except sec. 16-10 and 16-11
TRANSCRIPT
Chapter 16: Polymers
Reading
All of Ch. 16 except
Sec. 16-10 and 16-11.
Homework No. 12
Problems 16-8, 16-10
Polymers• Natural polymers
• Synthetic polymers
Examples of natural polymers
• Cellulose (e.g., wood, wool, cotton)
• Starches
• Proteins
• Natural rubber
Examples of synthetic polymers
• Polyethylene
• Polyvinyl chloride
• Synthetic rubbers
(PVC)
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Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Addition polymerization
.OH is the initiator.
Degree of polymerization
= No. of mers in a molecule
= Molecular mass / mer mass
Molecular mass is Mi for size interval i.
Population described asNumber fraction of molecules in size interval i = Xi
= No. of molecules in size interval i divided by No. of molecules in polymer
Number-average molecular mass = Σi(XiMi)
Population described asMass fraction of molecules in size interval i = Wi
= Mass of molecules in size interval i divided by mass of molecules in polymer
Mass-average molecular mass = Σi(WiMi)
Number-average molecular mass < Mass-average molecular mass
Example problem
• 18 g sugar (C6H12O6, M = 180 g/mole)
18 g water (H2O, M = 18 g/mole)• No. of molecules of sugar = 18/180 = 0.1 mole No. of molecules of water = 18/18 = 1.0 mole• Mass-average molecular mass = (0.50) (180 g/mole) + (0.50) (18 g/mole) = 99 g/mole• Number-average molecular mass = (0.1/1.1) (180 g/mole) + (1.0/1.1) (18 g/mole) = 32.7 g/mole
Polymer blend (a solid solution)
Homopolymer: 1 type of mer Copolymer: >1 type of mer
Copolymer
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Styrene-butadiene block copolymer
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Polyamide
Condensation polymerization
Polyester
Polyamide
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FunctionalityNo. of reaction sites in a
monomer for polymerization
= 2 for linear polymers
>2 for network (3D) polymers
Due to stereohindrance, functionality = 3, i.e., each phenol ring is at most linked to 3 other phenol rings. One water molecule is formed per bridge.
Network polymer
Kinked conformation
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Isomers
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Isotactic
Syndiotactic
Atactic
No side group
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Isotactic
Syndiotactic
Atactic
Tacticity
Fractions that are
atactic,
syndiotactic and
isotactic
Branching
Types of polymer
• Thermoplastic (softens upon heating)
• Thermoset (does not soften upon heating)
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Compression molding
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Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Necessary but not sufficient conditions for elastomers
• Noncrystalline at room temperature
• Glass transition temperature well below room temperature
• Macromolecular chains
- very long with many bends
- in constant motion at room temperature
- cross-linked every few hundred atoms
Degree of crystallinity
Degree of crystallinity = Fraction of the polymer that is crystalline
For the same cooling rate, different polymers have different tendencies toward crystallinity
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Crystalline region
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Orthorhomic unit cell of polyethylene
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Network polymers
Glassy usually, because rearrangement is difficult.
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Linear polymersFactors that affect the tendency toward crystallinity1. Character of the side groups (a) Bulkiness of the side groups (b) Arrangement of the side groups2. Amount of chain branching3. Macromolecular chain length (long molecules tend to
be kinked)4. Homopolymers tends to be more crystalline than
copolymers
Effect of the degree of crystallinity
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Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Copyright © 2006 by Nelson, a division of Thomson Canada Limited
Description of a polymer
• Mer(s)• Type of copolymer• Molecular mass (degree of
polymerization)• Tacticity • Degree of crystallinity