Organic Chemistry Lesson # 5 Polymers Organic Chemistry Lesson # 5

Background Information Polymer – a very large molecule that is built of repeating units of monomers (single molecules). When all the units are identical, it is called a homopolymer, and when the units are two alternating molecules, it is called a copolymer. Natural polymers are made by all living things – these include starch and cellulose (polymers made from glucose), proteins and DNA. We will discuss these at the end of this lesson. Synthetic polymers are made by scientists and often resemble natural polymers. Some examples include chewing gum, glue, polyester, Styrofoam, non-stick coatings, Nylon, Kevlar, rubber, plastic and vinyl.

Addition Polymers Addition polymers are formed from the addition reaction between alkene monomers. The double bonds must break in order for each monomer to join to the next. Note that the naming stems from the original alkene versus the unsaturated polymer chain.

Example 1: Polyethene (plastic containers)

Example 2: Polychloroethene (Polyvinyl chloride – PVC – insulating wires, raincoats, upholestery)

Example 3: Polypropene (rope, carpet)

Plastics Synthetic polymers that can be moulded into shape (often under heat and pressure) and will then retain their shape when cooled. Most are unreactive, as they are held together by stable single C-C bonds. This means that they resist breakage and can hold food and liquid well, but it also means that they are difficult to break down once thrown in the garbage.

Plastics Since plastics contain non-polar C-C and C-H bonds, they have weak London dispersion (Van der Waals) forces holding each plastic polymer to the next. This holds them in a rigid shape. If you want a more flexible plastic, heating up the polymers disrupt the intermolecular forces allowing the plastic to flex and stretch. Sometimes when two polymer chains come in contact with one another, they can form additional bonds between their strands called cross-linking. Cross-links make polymers incredibly strong and less flexible.

Condensation Polymers Condensation polymers are formed from condensation reactions between two monomers that have two reactive functional groups on each end. Water or some other small molecule is also produced in the reaction. Polyesters are formed between carboxylic acid and alcohol monomers, with their functional group appearing twice – once on each end of the molecules (diacids, diols). Many clothing items not made of natural fibres are made from polyesters.

Polyester Example: Propan-1,3-dioic acid + Propan-1,2-diol

Polyamide Example: Butan-1,4-dioic acid + Ethan-1,2-diamine Polyamides are formed between carboxylic acid and amine monomers. Common polyamides include Nylon and Kevlar.

Readings “The Invention of Nylon” – answer questions # 1-4. “Polymers and Industry” and “Polymer Production: Risks and Solutions” – answer questions # 19-24. “Natural Polymers” – answer questions # 1-7.