Chapter 16: Polymers

Reading All of Ch. 16 except Sec and

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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Addition polymerization.OH is the initiator.

Degree of polymerization = No. of mers in a molecule = Molecular mass / mer mass

Molecular mass is M i for size interval i.

Population described as Number fraction of molecules in size interval i = X i = No. of molecules in size interval i divided by No. of molecules in polymer Number-average molecular mass = Σ i (X i M i )

Population described as Mass fraction of molecules in size interval i = W i = Mass of molecules in size interval i divided by mass of molecules in polymer Mass-average molecular mass = Σ i (W i M i )

Number-average molecular mass < Mass-average molecular mass

Example problem 18 g sugar (C 6 H 12 O 6, M = 180 g/mole) 18 g water (H 2 O, 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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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. Styrene-butadiene block copolymer

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©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. Polyamide Condensation polymerization

Polyester Polyamide

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Functionality No. 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

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. 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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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

Copyright © 2006 by Nelson, a division of Thomson Canada Limited Crystalline region

Copyright © 2006 by Nelson, a division of Thomson Canada Limited Orthorhomic unit cell of polyethylene

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Copyright © 2006 by Nelson, a division of Thomson Canada Limited Linear polymers Factors that affect the tendency toward crystallinity 1.Character of the side groups (a) Bulkiness of the side groups (b) Arrangement of the side groups 2.Amount of chain branching 3.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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Description of a polymer Mer(s) Type of copolymer Molecular mass (degree of polymerization) Tacticity Degree of crystallinity