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CHAPTER 14 Polymer Structures. H. H-C-H. Similarly. H. Methane. Ethylene. Covalent Bonding. INTRODUCTION. Natural Polymers Leather, wood, rubber, cellulose, cotton, wool. Synthetic polymers Synthesized from small organic molecules. CHEMISTRY OF POLYMER MOLECULES. - PowerPoint PPT Presentation
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ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.1
CHAPTER 14CHAPTER 14
Polymer Structures
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.2
INTRODUCTION
Natural Polymers Leather, wood, rubber, cellulose, cotton, wool.Synthetic polymers Synthesized from small organic molecules.
CHEMISTRY OF POLYMER MOLECULES
Hydrocarbons (many organic materials)= composed of hydrogen and carbon
Covalent Bonding
H-C-H
H
H
Methane Ethylene
Similarly
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.3
POLYMERISATIONMers = small structural entities making up the ‘poly’mer.
Ethylene(C2H4) gas
CAN BE CONVERTED TO POLYETHYLENE(PE) Solid
Catalyst
bonding satisfied for C atom
bonding unsatisfied for this C atom
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.4
Angle =109o
RESULT
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.5
Similarly
Methyl group
Unpaired electron
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.6
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.7
MOLECULAR WEIGHT Number average
Weight-average
Not all chains same length
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.8
Molecular weight of mer j
Degree of polymerizationFor copolymers
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.9
Linear Branched
Crosslinked Networke.g. Epoxy e.g. Rubber
e.g. Polyethylene, Nylon
Lower density
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.10
COPOLYMERSPolymers composed of two or more different ‘mer’ units
HOMOPOLYMERS
Bifunctional, trifunctional mers
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.11
Styrene-butadiene rubber (SBR) random copolymerUsed in automobile tires.
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.12
POLYMER CRYSTALLINITY
= Packing of molecular chains so as to produce an ordered atomic array.
Small molecules (Methane, H2O) either either totally crystalline (as solids) or amorphous (as liquids)
However POLYMERS only partially crystalline (semi-crystalline)Max. crystallinity ~ 95%.
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.13
Crystalline polymer = higher density
Properties greatly affected by degree of crystallinity (crystalline = stronger and more resistant to softening by heat. important to quantify degree crystallinity
ME 260: Introduction to Engineering Materials
Chapter 15. Polymer Structures 14.14
Slower cooling rates from the melt favor higher crytallinity (giving time for ordered configurations)
Linear Polymers Crystallization easily accomplished, since no restriction to chain alignment
Branched polymers NEVER highly crystalline Side branches interfere with crystallization Network Polymers AMORPHOUS
COPOLYMERS
More Irregular and random mer less crystallinity
Alternating and block copolymers likelihood of crystallization.
Random and Graft copolymers Normally Amorphous
