Polymers I

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Polymer I:

Polymer I Polymerization, Polymer Structure, Morphology

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Objectives Explain the basic steps in polymerization.

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Objectives Explain the basic steps in polymerization. Explain the epoxy/amine reaction mechanism.

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Objectives Explain the basic steps in polymerization. Explain the epoxy/amine reaction mechanism. Identify the grafting/copolymer structures and/or name them.

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Objectives Explain the basic steps in polymerization. Explain the epoxy/amine reaction mechanism. Identify the grafting/copolymer structures and/or name them. Identify or sketch the various isomeric structures possible with a vinyl polymer.

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Objectives Explain the basic steps in polymerization. Explain the epoxy/amine reaction mechanism. Sketch/identify the four basic vinyl molecules Identify the grafting/copolymer structures and/or name them. Identify or sketch the various isomeric structures possible with a vinyl polymer. Explain the basis for polymer crystallinity.

Polymer Building Blocks:

Polymer Building Blocks Hydrogen Carbon (key) Oxygen Nitrogen Fluorine Silicon Sulfur Chlorine

Carbon Is Key:

Carbon Is Key Atomic number: 6 Valence: 2s 2 2p 2 Hybrid orbital- sp Will share up to four electrons, tetrahedral arrangement

Polymerization Processes:

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 shared electron pair. A polymer is formed by catalyzing the formation of a free radical:

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Addition Polymerization

Condensation Reaction:

Condensation Reaction

Effects of Polymerization Scheme:

Effects of Polymerization Scheme Polymer may contain residual byproduct. Addition polymerization done in solvent may have residual solvent Cleanest polymers are gas phase or aqueous solution polymers

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Basic Steps in Polymerization Initiation: Formation of free radical Propagation: Combining of mers to form chains Termination: Elimination of free radicals

Polymerization Step Effects :

Polymerization Step Effects The actual method of initiation, propagation, termination will affect final properties. You cannot easily switch suppliers or resin once a particular material and factory have been qualified.

Properties :

Properties Behavior determined by a combination of primary backbone bonds and secondary bonds. Different monomers will have different secondary bond strengths.

Levels of Polymer Architecture:

Levels of Polymer Architecture Monomer Type

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Families based on an ethenic backbone are vinyl polymers or vinylydines Polyethylene PE Polypropylene PP

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Polystyrene PS Polyvinylchloride PVC

Levels of Polymer Architecture:

Levels of Polymer Architecture Monomer Type Molecule Length

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Molecular Weight: Number Average Weight Average

Levels of Polymer Architecture:

Levels of Polymer Architecture Monomer Type Molecule Length – molecular weight Mixture of Monomers - copolymers

Types of Copolymers:

Types of Copolymers Homopolymer AAAAAAAAAAA Random CCACBBACABAA Alternating ABCABCABCABC Block AAAABBBBCCCC Graft

Levels of Polymer Architecture:

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

Levels of Polymer Architecture:

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

Polyester Reaction:

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

Levels of Polymer Architecture:

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 (collections of lamellar crystalites) Spherulite (no shear) Row Nucleated (shear ) Shish-kebab

Levels of Polymer Architecture:

Levels of Polymer Architecture Monomer Type Molecule Length – molecular weight Mixture of Monomers – copolymers Monomer Arrangement – Isomers Bond/Network Structure Molecular Conformation Blends/Alloys

Polymer Blends:

Polymer Blends Mixture of compatible polymers No primary bonds Intermediate properties May be phase separation

Levels of Polymer Architecture:

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

Polymer Categories: Network:

Polymer Categories: Network Thermoset vs Thermoplastic Network vs Linear Fixed vs Reshapeable

Polymer Categories: Price:

Polymer Categories: Price Commodity <$1/pound Engineering $1.5-$5/pound Specialty > $5/pound

Polymer Categories: Application:

Polymer Categories: Application Plastics Adhesives Films Fibers Elastomers

Self-Test:

Self-Test Draw the monomer structure of polyethylene. What crystalline morphology forms under shear? Which type of polymer cannot be reshaped by heat and pressure?

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