Lecture 01: Characteristics of Polymers

Polymers Everywhere

• Polymers are widely used in food packaging, transportation, medical supplies, clothing, construction, manufactured goods, and electronics.

Variety of Polymers

• Polymers are categorized into plastics, elastomers (rubber), fibers, coatings, adhesives, foams, and films.

Importance of Polymers

• Polymers can be molded into intricate shapes with minimal further processing.
• They are cost-competitive with metals on a volumetric basis.
• Polymers generally require less energy to produce than metals.
• Some plastics are transparent, competing with glass in certain applications.
• They are easy to process through methods like injection molding.
• Polymers are lightweight, tough, flexible, and generally insulating.

Why Study Polymers

• Engineers should understand polymers due to their wide range of applications.
• Understanding polymer deformation mechanisms allows for control of elasticity and strength.
• Additives can modify properties such as strength, abrasion resistance, and flammability.

Basics of Polymers

• Polymers mainly consist of carbon, hydrogen, oxygen, nitrogen, and chlorine atoms.
• Less common elements include sodium, calcium, silicon, sulfur, fluorine, bromine, phosphorus, and magnesium.

Carbon

• Carbon is a crucial element in plastics due to its four outer shell electrons, enabling it to form stable single, double, or triple bonds with itself.
• It can form chains of almost any length.

Covalent Bonds

• Covalent bonds form when atoms share electrons to achieve a stable configuration, typically between nonmetals.

Key Characteristics of Covalent Bonds

• Atoms share electrons in pairs to create stable configurations.
• Covalent bonds are strong and require energy to break.
• Types include single (one shared electron pair), double (two shared pairs), and triple (three shared pairs) bonds.

Van der Waals Bonds

• Van der Waals forces are weak attractive forces between all atoms and molecules.

Key Characteristics of Van der Waals Forces

• Arise from fluctuations in electron distribution, causing temporary charge differences.
• Weaker than covalent bonds, influencing physical properties like melting and boiling points.

Difference Between Covalent and Van der Waals Bonds

• Covalent bonds are stronger and involve electron sharing to form molecules.
• Van der Waals forces are weaker, non-directional intermolecular attractions.

Hydrocarbon Covalent Bonds

• Hydrocarbons, composed of carbon and hydrogen, form the basic structure of polymers with covalent bonds.
• Carbon atoms share electrons to form linear or branched chains, commonly with single covalent bonds.
• Multiple bonds, like double and triple bonds, can also occur.

Hydrocarbon Cyclic (Aromatic) Bonds

• Hydrocarbons include cyclic structures with single or double bonds.

What is a Polymer?

• Polymers are large molecules made of repeating monomer units connected by covalent bonds.
• Covalent bonds give polymers strength, flexibility, and thermal properties.
• Weaker Van der Waals forces also contribute to physical properties.

Repeating Units Examples

• Polyethylene (PE), Polyvinyl chloride (PVC), Polypropylene (PP)

Effect of Covalent Bonds on Polymer Properties

• Single bonds: Polymers are flexible and chemically resistant.
• Double bonds: Polymers are rigid and chemically reactive.
• Triple bonds: Polymers are stiff and highly conductive.

Characteristic Structures of Common Polymers

• Includes Polyethylene, Polypropylene, Polystyrene, Polyamide 6, Polyamide 66, Polyethylene terephthalate, Polyvinyl chloride, Epoxy resin, and Melamine-formaldehyde resin.

Effect of Oxygen Atoms

• Increases chemical reactivity, hydrophilicity, flammability, and biocompatibility of polymers.

Effect of Nitrogen Atoms

• Can alter chemical reactivity and hydrophilicity; improves flammability resistance and biocompatibility.

Effect of Chlorine Atoms

• Enhances chemical resistance and hydrophobicity; acts as flame retardant but may have limited biocompatibility and environmental concerns.

Effect of Aromatic Unit

• Provides chemical resistance, hydrophobicity, UV resistance, and rigidity; may have limited biocompatibility.