Polymers are large molecules made by linking together many smaller molecules, called monomers. monomer symbol n Natural polymers include proteins, carbohydrates and lipids. Synthetic polymers include plastics, nylon, acetate, and polyesters. Polymerization reactions can either be classified as addition reactions or as condensation reactions.

Addition Polymers Addition polymerization is a reaction where monomer units join each other in a process that involves the rearranging of electrons in double or triple bonds in the monomer. Ethene (ethylene) has two pairs of shared electrons in the double bond. - - C C High temperature or UV light can cause two of these shared (paired) electrons to become unshared (unpaired). - -

Polyethene (Polyethylene or Vinyl)

Here’s another way to see the chain reaction Here’s another way to see the chain reaction. These are the carbon atoms with their double-bond (2 shared electrons each). The hydrogen atoms are not shown. A collision breaks the first bond. Once the first double bond is broken, a chain reaction will occur. In about a second an entire chamber of compressed ethylene gas turns into the polymer, polyethylene.

When the chains get up to 500,000 carbons long, they are tough enough for synthetic ice, replacement joints, and bullet-proof vests. This is called high density polyethylene (HDPE). See p. 139 in textbook

Low density polyethylene (LDPE) is made by causing the long chains of ethylene to branch. That way they cannot lie next each other, which reduces the density and strength of the polyethylene. This makes the plastic lighter and more flexible.

Low density polyethylene is used to make things like plastic bags, plastic wrap, and squeeze bottles.

Polypropene It is more commonly called polypropylene. Polypropylene is used to make things like carpet, rope and thermal underwear.

Polyvinyl Chloride PVC is one of the most widely used polymers, with dozens of practical applications.

PolyVinyl Chloride (or PVC) is almost the same as polyethylene, except every second hydrogen is replaced with a chlorine atom (green sphere).

Polyvinyl Chloride (PVC) upholstery siding wire insulation raincoats pipes and fittings

Polyvinyl Alcohol Uses include – white glue, post it notes, “silly puddy”, “slime” etc…..

Polystyrene When a benzene ring is attached to an ethene molecule, it is commonly called styrene.

Polystyrene trays cups coolers packing materials

Teflon Teflon® is the product name for the polymer used to make nonstick cookware. It is composed of a series of tetrafluoroethene monomers. Recently, concern has been growing regarding the possibility that Teflon® releases toxic chemicals if it gets too hot.

Important constitutions for synthetic polymers 19 19

Crosslinking By using another atom – C group or OH or S the polymer can be strengthed and also control of the structure can be forced

Condensation Polymers Condensation polymerization involves the formation of a small molecule (like H2O, NH3, HCl) from the functional groups of two different monomer molecules. The monomer molecules then bond at the site where the atoms have been removed. A synthetic compound that has a similar chemical structure to a naturally occurring substance is called a structural analog. Functional analogs are synthetic compounds that perform the same function as a naturally occurring substance but do not necessarily have similar structures (e.g. artificial sweeteners).

Dehydration Reaction

dicarboxylic acid + polyalcohol → polyester + water Polyesters A polyester is a series of ester molecules joined in a long chain. dicarboxylic acid + polyalcohol → polyester + water The dicarboxylic acid has a carboxyl group at each end of the molecule and the polyalcohol (a diol) has a hydroxy group at each end. This makes the formation of a long chain of esters joined together possible. esterification

Notice two carboxyl groups at the ends of each carboxylic acid. Notice two hydroxyl groups at the ends of each alcohol.

Nylon Nylon is a synthetic structural analog to proteins, a natural product.

Nylon was synthesized as a substitute for silk, a natural polyamide. The Hydrogen bonding cross linking of the Nylon gives it it’s strength.

Kevlar The polymer chains form a strong network of hydrogen bonds that hold adjacent chains together in a sheet-like structure.

Formation of a polyamide

Formation of a polyamide + H2O

Formation of a polyamide + H2O + H2O

Formation of a polyamide + H2O + H2O + H2O

Formation of a polyamide A polyamide “backbone” forms with R groups coming off. This protein is built with amino acids.