Unit 1: Polymer Chemistry

The Bonding of Carbon To the right of the staircase on the periodic table It is a non-metal Has 4 valence electrons meaning it will form 4 bonds Carbon forms a variety of covalent compounds with other carbon atoms or other non-metals

The Bonding of Carbon As was covered in CH1120, carbon can form polar covalent bonds In polar covalent bonds carbon and the other atom in the bond have an electronegativity difference (ΔEN) between 0.4 and 2.0

Hydrocarbons Compounds containing only hydrogen and carbon These are often arranged in “chains” or “rings”

Diagrams Structural (Lewis) Condensed Line (Geometric)

Homologous Series Group of organic compounds with similar structure Structure varies only by the number of atoms in the chain Alkanes: CnH2n+2 Alkenes: CnH2n Alkynes: CnH2n-2

Naming Straight Chain Alkanes CH4 - Methane C2H6 - Ethane C3H8 - Propane C4H10 - Butane C5H12 - Pentane C6H14 - Hexane C7H16 - Heptane C8H18 - Octane C9H20 - Nonane C10H22 - Decane

Multiple Bonds There can be single, double or triple bonds within carbon compounds With all single bonds: Alkane With a double bond: Alkene With a triple bond: Alkyne

Functional Groups Groups used to differentiate organic compounds Have their own characteristics “R” represents a carbon chain Compounds can contain more than one functional group

Aromatics Single bond: Double bond: Triple bond: 1 Sigma (σ) bond 1 Sigma (σ) bond, 2 Pi (π) bonds Triple bond: 1 Sigma (σ) bond, 3 Pi (π) bonds

Aromatics

Aromatics Delocalized π bonds stabilize structures Flat rings with delocalized π bonds are said to be aromatic Delocalized π bond is represented with a circle within the ring

Aromatics

Alcohols -OH group in chain

Carboxylic Acids -COOH group in chain

Esters -COOR group in chain

Ketones C double bonded to O with 2 carbon chains

Aldehydes C double bonded to O with 1 carbon chain and 1 hydrogen

Aldehydes Vs. Ketones

Ethers Oxygen within then chain

Amines Nitrogen containing 3 bonds contain at least one carbon chain (the others can be carbon chains or hydrogen)

Amines Primary (1⁰) Secondary (2⁰) Tertiary (3⁰) 1 carbon chain 2 hydrogen Secondary (2⁰) 2 carbon chains 1 hydrogen Tertiary (3⁰) 3 carbon chains

Amides Nitrogen containing Like amines but carbon directly bonded to nitrogen is double bonded to oxygen (C=O is called carbonyl group)

Polymers AKA Plastics Large molecules (macromolecules) made of many repeating units Formed through polymerization Natural Wool, silk, biopolymers (carbohydrates, proteins) Synthetic (focus of this course)

Monomers “one part” Molecule that chemically bonds to other molecules to create a polymer

Repeating Units Polymers are long chains of repeating units Monomers are changed in order to fit into the chain

Industrial Examples

Physical Properties Bonds allow atoms to move around making the molecular chain flexible Macromolecules have different molecular weights Sometimes distributed evenly Sometimes concentrated in one area of chain Causes polymers to soften over time (no sharp melting point) Holding various chains together can make polymers harder, denser, less soluble, more resistant to heat

Polymers Homopolymer Copolymer Single monomer repeated Multiple monomers present Random Blocked Graft

Linear Polymers Straight chain polymers Consist of a straight chain of C-C bonds Actual shape of each carbon is tetrahedral

Branched Polymers Replacement of a substituent (ie. hydrogen atom bonded to the polymer chain) with a chain of carbon atoms Added chain can be the same as original polymer or may be different

Network Polymers More rigid than branched or linear Chemical bonds are introduced between polymer chains

Cross-linking Forming of chemical bonds between polymer chains More cross-links = more rigid/stronger Plastic wrap vs. juice container

Plastics Solid polymers that can be formed into various shapes by applying heat and pressure Thermoplastics Thermosetting plastic Elastomers

Thermoplastics Can be reshaped Polymer can be melted down and recycled Milk containers, pop bottles

Thermosetting (Thermoset) Plastics Cannot be reshaped readily Shaped through irreversible chemical processes Many adhesives, fibreglass, nylon, polyester

Thermoplastics Vs. Thermoset

Elastomers Exhibit rubbery/elastic behaviour Regain shape after stretching or bending Crosslinking present but not as 3D/close as thermoset Rubber

Polymers in Industry Strength and flexibility gives a variety of uses Resistant to oxidation Reinforcing material can be added to make an even stronger product (ie. Fibreglass)

Intermolecular Forces Polymers such as polypropylene and polystyrene are non-polar Contain only London forces

Intermolecular Forces Most functional groups are polar, adding them makes the polymer polar With polarity brings in the possibility of Dipole- dipole interactions and Hydrogen bonding More functional groups increases intermolecular forces

Intermolecular Forces Polymers sometimes have weak intermolecular forces (London) but since they are so large there are many points of interaction Chain entanglement Polymers move slowly even when heated

Intermolecular Forces Higher molecular weight means the polymer chain is longer Larger molecules have more points of interaction therefore more intermolecular forces Remember from CH1120, stronger/more intermolecular forces increases boiling and melting points

Distance of Separation When chains are closer together they will interact more (more intermolecular forces) Half the distance doubles the intermolecular force

Distance of Separation High Density Polyethylene (HDPE) Mostly straight chains Packed tightly together More intermolecular forces Lawn furniture, fuel tanks Strength more important than flexibility

Distance of Separation Low Density Polyethylene (LDPE) Branched chains Cannot pack as tightly as HDPE Fewer intermolecular forces Plastic wrap, grocery bags Flexibility more important than strength

Reactions Carboxylic Acid + Sodium Hydroxide Neutralization reaction, yields a salt and water

Reactions Carboxylic Acid + Alcohol Must add heat (energy/Δ) and acid (H+) Yields an ester and water

Reactions Amine + Hydrochloric Acid Nitrogen will gain a positive charge by accepting the extra hydrogen Chlorine becomes an anion

Reactions Carboxylic Acid + Amine Temperature must be >100⁰C Only 1⁰ and 2⁰ amines OH from acid and H from amine combine Yields an amide and water

Polymerization Always the same steps: Two types Initiation Propagation Termination Two types Free radical addition polymerization C=C is broken Condensation polymerization Water is removed

Free Radical Addition Polymerization 1. Initiation Form a free radical (highly unstable/reactive) Non-polar compounds can be cleaved to give free radicals X2  2X• Addition of energy is needed (heat or light)

Free Radical Addition Polymerization 2. Propagation Free radical attacks the monomer to create a new free radical

Free Radical Addition Polymerization 2. Propagation Continued This step continues as the new free radical continues to attack new monomers New monomers are added to the chain and new free radicals are formed

Free Radical Addition Polymerization 3. Termination Collision with another chain or a free radical causes the propagation to come to an end The same free radical may be added that was used in the initiation stage

Free Radical Addition Polymerization Know the mechanisms to create: Polypropylene Polystyrene Polyvinyl chloride (PVC)

Free Radical Addition Polymerization (Polypropylene)

Free Radical Addition Polymerization (Polystyrene)

Free Radical Addition Polymerization (Polyvinyl Chloride) Polyvinyl chloride (PVC)

Copolymerization (Styrene Butadiene Rubber)

Copolymerization (Styrene Butadiene Rubber) Double bonds will be in alternating positions Styrene and butadiene will also alternate

Condensation Polymerization As the polymer grows water is released as a product

Condensation Polymerization Two types: Polyester Formation Dicarboxylic Acid + Dialcohol  Polyester+ Water -OH is lost from acid, -H from alcohol to make H2O Initiation: requires heat and strong acid Termination: cool and neutralize Polyamide Formation Dicarboxylic Acid + Diamine  Polyamide + Water -OH is lost from acid, -H from amine to make H2O Initiation: heat above 100⁰C Termination: cool below 100⁰C

Condensation Polymerization (Polyester) Dicarboxylic Acid + Dialcohol Polyester + Water Acid and heat are required for reaction Termination is carried out by cooling and neutralizing

Condensation Polymerization (Polyester)

Condensation Polymerization (Polyester)

Condensation Polymerization (Polyamides) “Nylon” is the common term used for polyamides Dicarboxylic Acid + Diamine  Polyamide + Water A temperature of greater than 100℃ is required Termination is carried out by cooling below 100℃

Condensation Polymerization (Polyamides)

Condensation Polymerization (Polyamides)

Formation of Acetate Cellulose + Acetic Acid  Acetate Cellulose is already a natural polymer, we alter it with acetic acid Sulfuric acid and heat are needed to speed up reaction

Formation of Acetate

Formation of Rayon Cellulose + NaOH + CS2  Rayon Cellulose is a naturally occurring polymer, in this case we alter it by adding sodium hydroxide and carbon disulfide

Formation of Rayon