2.1 Introduction to Polymers

Where do we get silk?

Monomers --> are small, repeating molecular units that make up polymers. Polymers --> Are large, chain-like molecules that are built from repeating units called monomers. Polymerization --> is a chemical process by which monomers are joined to form polymers.

Homopolymer --> a polymer formed by reactions only involving a single type of monomer. Figure 1: Polypropene and polystyrene form by addition reactions of its monomers

Copolymer --> a polymer made up of two or more different types of monomers. Figure 2: Condensation reaction of 3 amino acids to form part of a silk polymer (a copolymer)

Polymers: Useful Properties The idea for the __________ was conceived in 1974 by Arthur Fry as a way of holding bookmarks in his hymnal while singing in the church choir. He was aware of an adhesive accidentally developed in 1968 by fellow 3M employee Spencer Silver. No application for the lightly sticky stuff was apparent until Fry's idea. The 3M company was initially skeptical about the product's profitability, but in 1980, the product was introduced around the world. Today, ______________ are sold in more than 100 countries.

2.2 Synthetic Addition Polymers

Synthetic Addition Polymers --> are very long organic molecules formed as the result of addition reactions between monomers with unsaturated carbon-carbon bonds. Example: PTFE is an abbreviation for Teflon, the slippery surface that prevents eggs from sticking to the pan. 2.2 Synthetic Addition Polymers

Teflon Is an inert, non-flammable material. Its unreactivity is due to the strong C-F bonds present (very resistant to chemical change). Used for electrical insulation, non-stick coating on cooking utensils, low-friction surface coatings, etc.

Other Addition Polymers Can be made from monomers containing methyl-, chloro-, cyano- and phenyl- substituents. Each leading to a wide range of properties. In each case, the carbon-carbon double bond becomes a single bond.

Drawing a Polymer Draw a structural diagram showing three repeating units of the addition polymer formed from cis-but-2-ene.

Drawing a Monomer Draw a structural diagram of the monomer used to make Saran. Use the polymer, circle the repeating unit, and then replace the single bond in each unit with a double bond. Each unit is now represented as a separate monomer.

Drawing a Monomer

Example 1: PVC is a Polymer of the Chloroethene Monomer Used in pipes, construction materials, tiles, clothing, reusable bags, etc.

Example 2: Polystyrene is a Polymer of the Styrene Monomer Used in heat-resistant disposable drinking cups, plastic toys, food containers, packaging material, etc.

Plastic Is a synthetic polymer that can be molded under heat and pressure and that retains its given shape. There are many plastics including polymers of substituted ethene molecules: polystyrene, polyvinyl, nylon, polyesters, rubber, etc. Manufactured from petrochemicals.

Plastic is chemically unreactive. held together by stable, single bonds. Since these C-C bonds are much stronger than C=C bonds, many resulting polymer molecules act as a good replacement for glass Some plastics are weakened to be used for other applications have atoms that are attracted to one another by London Dispersion/Van Der Waals forces (weak) but since these forces are additive, polymer chains are generally stronger.

Plastic have atoms that are attracted to one another by London Dispersion/Van Der Waals forces (weak) but since these forces are additive, polymer chains are generally stronger because they often thousands of carbon atoms long Most plastics become softer and more flexible when heated. The polymer chains can slide past each other and plastic becomes stretchy and flexible. Van der Waal forces allow the plastic to flex and stretch

LDPE vs. HDPE Branches in polymer chains (in LDPE) prevent molecules from packing tightly. These plastics are much softer and more flexible because of the molecules’ greater range of motion. Polymer chains in HDPE have molecules that are tightly packed and that are more restricted. These plastics are hard and rigid and have a specific shape. LDPE is made by adding small amounts of compounds, such as butadiene, that have two or more double bonds. The butadiene results in branches in the polymer chains.

Plasticizers Substances that are added to plastics to increase flexibility. Make it easier to shape into useful objects. These molecules are placed between polymer chains keeping the chains spaced apart and weakening the forces that hold the molecules in place.

Cross-Linking Polymers form from monomers that join. Depending on the functional groups present within the monomers, individual chains of polymers can link together through chemical bonds occurring between individual strands. This causes polymers to form networks. The more cross-linkages there are, the more tightly chains are held together, the more rigid and inflexible the polymer.

Properties of Polymers Depend On: functional groups present the number of monomers in the polymer molecule the degree of cross-linking that occurs

Plastics Classification Thermoplastics: are not crosslinked and can withstand heat. They can be formed when heated and hold their shape when cooled Elastomers: have wide-meshed cross-linking. They can be stretched and snap back to their original shape. Thermosets: have closely-meshed crosslinking. They can not be softened after heating.

Career: Polymer Scientist

Class Work Page 83 #1,2 Page 87 #1-3 Page 93 #4 You are responsible for knowing the following polymers: polyethene, polypropene, PVC, Teflon, and Polystyrene