19 Polymers I
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Transcript of 19 Polymers I
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Polymer IPolymerization, Polymer
Structure, Morphology
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Objectives
1. Explain the basic steps in polymerization.
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Objectives
1. Explain the basic steps in polymerization.
2. Explain the epoxy/amine reaction mechanism.
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Objectives
1. Explain the basic steps in polymerization.
2. Explain the epoxy/amine reaction mechanism.
3. Identify the grafting/copolymer structures and/or
name them.
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Objectives
1. Explain the basic steps in polymerization.
2. Explain the epoxy/amine reaction mechanism.
3. Identify the grafting/copolymer structures and/or
name them.
4. Identify or sketch the various isomeric structures
possible with a vinyl polymer.
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Objectives
1. Explain the basic steps in polymerization.
2. Explain the epoxy/amine reaction mechanism.
3. Sketch/identify the four basic vinyl molecules
4. Identify the grafting/copolymer structures and/or
name them.
5. Identify or sketch the various isomeric structures
possible with a vinyl polymer.
6. Explain the basis for polymer crystallinity.
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Polymer Building Blocks
Hydrogen
Carbon (key)
Oxygen
Nitrogen
Fluorine
Silicon
Sulfur
Chlorine
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Carbon Is Key
Atomic number: 6
Valence: 2s22p2
Hybrid orbital- sp
Will share up to four
electrons, tetrahedralarrangement
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Polymerization Processes
Addition Polymerization
• No Byproducts
• Usually heat driven
Condensation Polymerization
• Byproducts produced
• Removal of byproduct controls rate
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Linear Addition
Begin with ethylene (gas)
Monomer or “mer”
Each bond is a sharedelectron pair.
A polymer is formed bycatalyzing the formation of a free radical:
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Addition Polymerization
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Condensation Reaction
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Effects of Polymerization Scheme
Polymer may contain residualbyproduct.
Addition polymerization done insolvent may have residual solvent
Cleanest polymers are gas phase oraqueous solution polymers
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Basic Steps in Polymerization
Initiation: Formation of free radical
Propagation: Combining of mers to formchains
Termination: Elimination of free radicals
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Polymerization Step Effects
The actual method of initiation,propagation, termination will affectfinal properties.
You cannot easily switch suppliers orresin once a particular material andfactory have been qualified.
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Properties
Behavior determined by acombination of primary backbonebonds and secondary bonds.
Different monomers will havedifferent secondary bond strengths.
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Levels of Polymer Architecture
Monomer Type
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Families based on an ethenic backbone arevinyl polymers or vinylydines
Polyethylene
PE
PolypropylenePP
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PolystyrenePS
PolyvinylchloridePVC
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Levels of Polymer Architecture
Monomer Type
Molecule Length
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Molecular Weight:
Number Average
Weight Average
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Levels of Polymer Architecture
Monomer Type
Molecule Length – molecular weight
Mixture of Monomers - copolymers
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Types of CopolymersHomopolymer AAAAAAAAAAA
Random CCACBBACABAA
Alternating ABCABCABCABCBlock AAAABBBBCCCC
Graft
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Levels of Polymer Architecture
Monomer Type
Molecule Length – molecular weight
Mixture of Monomers–
copolymers Monomer Arrangement - Isomers
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Isomerism/Polymer Tacticity
Isotactic
Sindiotactic
Random
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Levels of Polymer Architecture
Monomer Type
Molecule Length – molecular weight
Mixture of Monomers–
copolymers Monomer Arrangement – Isomers
Bond/Network Structure
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Polymer Categories
Thermoplastic – only secondary bonds between
molecules.-”Plastic” or reshapable
- Melted and formed under pressure
- Higher tooling costs
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Polymer Categories
Thermoplastic – only secondary bonds between
molecules.-”Plastic” or reshapable
- Melted and formed under pressure
- Higher tooling costs
Thermoset – primary and secondary bonds between
molecule segments.
- Cannot be reshaped
- Low viscosity in processing
- Cheaper tooling
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Epoxy Reaction:
Primary Amine
If an Amine is on
both ends you get a“crosslink”
Thermoset
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Polyester Reaction
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Thermoset
Frequent Cross-links Create 3-D Network
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Amorphous Polymer – Lightly Crosslinked
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Semicrystalline Thermoplastic
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Levels of Polymer Architecture
Monomer Type
Molecule Length – molecular weight
Mixture of Monomers–
copolymers Monomer Arrangement – Isomers
Bond/Network Structure
Molecular Conformation
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Amorphous
Example:
Polycarbonate
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Crystalline
Example: Polyethylene
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Crystals
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Chains assume folded
chain conformation
These collect into
lamellar crystallite
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Two crystalline morphologies
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Two crystalline morphologies
(collections of lamellar crystalites)
Spherulite (no shear)
Row Nucleated (shear )
Shish-kebab
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Levels of Polymer Architecture
Monomer Type
Molecule Length – molecular weight
Mixture of Monomers–
copolymers Monomer Arrangement – Isomers
Bond/Network Structure
Molecular Conformation Blends/Alloys
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Polymer Blends
Mixture of compatiblepolymers
No primary bonds Intermediate
properties
May be phaseseparation
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Levels of Polymer Architecture
Monomer Type
Molecule Length – molecular weight
Mixture of Monomers – copolymers
Monomer Arrangement – Isomers
Bond/Network Structure
Molecular Conformation
Blends/Alloys
Additives
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Polymer Categories: Network
Thermoset vs Thermoplastic
Network vs Linear
Fixed vs Reshapeable
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Polymer Categories: Price
Commodity <$1/pound
Engineering $1.5-$5/pound
Specialty > $5/pound
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Polymer Categories: Application
Plastics Adhesives
Films
Fibers
Elastomers
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Self-Test
Draw the monomer structure of polyethylene.
What crystalline morphology formsunder shear?
Which type of polymer cannot bereshaped by heat and pressure?