10.5 Polymerization These reactions involve the addition of many single “subunits” together to form giant molecules (macromolecules) called polymers. Polymers form the basis for the structure of living cells, since they form proteins, carbohydrates, fats and nucleic acids. Also, they are the basis for plastics and the plastics industry, a very economically important industry.

Polymers A polymer is a long chained molecule consisting of hundreds or thousands of small repeating units called monomers. These short chain molecules are ones such as ethane, ethene and vinylchloride in plastics or sugars and amino acids in carbohydrates and proteins.

Types of Polymerization Reaction The creation of polymers from monomers is generally by either: addition polymerization or condensation polymerization

Addition Polymerization In addition polymerization the monomers are alkenes or alkynes. The unsaturated bonds in these molecules are used to form bonds between the carbon atoms to form large chains that may be branched and cross-linked. No other product is produced in the formation of addition polymers

Examples of Addition Polymerization Polyethylene - used for plastic insulation for wires, plastic milk bottles, refrigerator dishes and laboratory wash bottles. H H H H l l l l ( C = C )n  H –(- C – C -)n- H l l l l H H H H ethene(ethylene) polyethylene

Polypropene Polypropene - commonly called polypropylene, it is used to produce things like carpet, rope and fleece base layers. H H H H l l l l ( C = C )n  H –(- C – C -)n- H l l l l H CH 3 H CH 3 propene polypropene(polypropylene)

Polyvinyl Chloride Polyvinyl chloride(PVC) - is used for insulation of electrical wires ans as a coating on fabrics used for raincoats and upholstery materials. H Cl l l l l ( C = C )n  H –(- C – C -)n- H l l H H chloroethene polyvinyl chloride (PVC) (vinyl chloride)

Polystyrene Polystyrene - used to make cups and containers and plastic cutlery. H H H H l l l l ( C = C )n  H –(- C – C -)n- H l l H H styrene polystyrene

Teflon Teflon - is the common name for polytetrafluoroethane. It is used to create non-stick surfaces on cookware. F F F F l l l l ( C = C )n  H –(- C – C -)n- H l l l l F F F F tetrafluoroethene polytetrafluoroethene(Teflon)

Condensation Polymerization A condensation polymerization is one in which the compounds combine by eliminating a small molecule such as a water molecule for each bond formed. The resulting polymer is called a condensation polymer. To form a condensation polymer the monomer molecules must be bifunctional, that is they must have two functional groups on the same molecule. Polyester and nylon are both synthesized by condensation polymerization.

Natural vs. Synthetic Polymers A synthetic structure that is similar to a naturally occurring substance is called a structural analog. Natural Product (food nutrient molecules) LipidsProteinsCarbohydrates Structural Analog (synthetic polymers) PolyestersNylonCellulose Polymers

Lipids Lipids are formed by esterfication between fatty acids (long-chain carboxylic acids) and glycerol (propane-1,2,3-triol). Because glycerol has three hydroxyl groups, it can react with three fatty acids to form a tri-ester. This reaction is not strictly speaking a polymerization reaction.

Polyesters Polyesters are formed when an alcohol reacts with a carboxylic acid in an esterfication reaction. The reactants form together into a single ester molecule. This reaction is repeated forming a polyester. This is accomplished using a dicarboxylic acid and a diol.

The formation of polyester

Proteins Condensation polymerization is common in living systems The production of proteins is from the condensation polymerization of amino acids There are only 20 different amino acids that remarkably form over 10 billion different proteins. They are formed through a reaction between a carboxylic group and an amine (-NH 2 ) group.

Proteins

Nylon Nylon forms in a similar way to proteins. It is a synthetic condensation polymer formed by reacting a carboxyl group and an amine group. Polymers with amide linkages are called polyamides Amide linkages in proteins are called peptide linkages and polymers are called polypeptides.

Nylon It was synthesized as a substitute for silk. During WWII production increased as it was used for parachutes, ropes, cords and even shoelaces. It is the amide linkage that make nylon such a strong fiber. When spun the polymer chains line up with one another and hydrogen bonding occurs between the chains.

Kevlar It is stronger than steel, but light enough to wear, it is used to make aircraft, sports equipment and bullet proof vests. This unique property is due to the hydrogen bonding between adjacent chains.

Carbohydrates The monomers of carbohydrates are simple sugars. Simple sugars undergo a condensation polymerization reaction in which water is formed and a larger molecule. (Polysaccharides)

Example

Starch vs. Cellulose Starchy foods provide energy because we can break them down. Cellulose on the other hand cannot be digested by humans, but provides a great source of dietary fibre.

Cellulose Acetates Cellulose acetate is a biopolymer. This is because it is a modification of a natural polymer. Cellulose reacts with acetic acid and acetic anhydride, with sulfuric acid as a catalyst.

Nucleic Acids Nucleic acids (DNA and RNA) are also natural polymers. They are formed by the polymerization of nucleotides:

The End