Polymers and Polymerization Polymers A polymer is a

Polymers and Polymerization

Polymers A polymer is a giant covalent molecule or macromolecule, made of many simple repeating units, known as monomers, joined together. Polymers are: � Long-chain molecules. � Found in nature, including cellulose in plants, starches in food, proteins and DNA in the body. � Also synthetic such as polyethylene and polystyrene, Teflon, and nylon.

Common Synthetic Polymers

Properties. The properties of a polymer depend on: � � � The bond type between monomers. The chemical nature of the monomers. The presence of bonding between the polymer chains, known as cross linkage

Polymerization � In polymerization, small repeating units called monomers are bonded to form a long chain polymer. Repeating monomer

Addition polymerisation � � � The monomer units of addition polymers all contain double bonds. The polymer bonds involve the carbon atoms which were involved in the double bond of the monomers. The polymer chain is the only product formed.

Example Polypropene is formed by the polymerisation of propene

Polymers from Addition Reactions

More Monomers and Polymers

Condensation polymerisation � � condensation polymerisation involves elimination of a 'simple' molecule (such as water) as monomer molecules join together. Polyesters, polyamides and proteins are all condensation polymers.

Polyesters � � In the reaction above, the acid and alcohol have just one functional group. To form a polyester, the monomers must have two functional groups per molecule.

� Polyesters are produced from repeating esterification reactions. � The hydroxyl (OH) and carboxylic acid groups (COOH) are at two positions (two reactive sites) on each reacting molecule

� � Condensation polymers are often made from two monomers - a diol and a dicarboxylic acid, or a diol and a diacid chloride. Terylene is the polyester formed from two different monomers: � ethan-1, 2 -diol (alcohol groups) � benzene-1, 4 -dicarboxylic acid (two acid groups). Monomer 1 ethan-1, 2 -diol HOCH 2 OH Monomer 2 benzene-1, 4 dicarboxylic acid (terephthalic acid)

Terylene

Polyamides � � � carboxyl group and an amino group react to form an amide or peptide link (-CONH-). The formation of many amide links produces a polyamide. Nylon is an example of a polyamide

Nylons have a variety of uses, from gear wheels to clothing. They are characterised by their: � Strength. � Elasticity. � Toughness. � Resistance to abrasion.

Nylons are formed by condensation polymerisation of either a dicarboxylic acid � or a diacid chloride with a diamine Nylon 6, 6, used as an artificial fibre in clothing, is produced from 1, 6 -diaminohexane (dissolved in water) and hexanedioic acid �

Making nylon

Nylon is a condensation polymer formed by combining a diamine with a dicarboxylic acid or diacyl chloride.

Nylon is a condensation polymer formed by combining a diamine with a dicarboxylic acid or diacyl chloride. We shall react diaminohexane, H 2 N–(CH 2)6–NH 2 with sebacoyl chloride, Cl. CO–(CH 2)8–COCl. Since our starting ingredients have 6 and 10 carbons, the nylon formed is called nylon 6, 10.

This acyl chloride has a relatively high molar mass, so is not very volatile and does not fume when the bottle is opened.

Make a solution of sebacoyl chloride by dissolving 1. 5 m. L in 25 m. L of tetrachloroethylene (an organic solvent). Why don’t we dissolve it in water? Because acyl chlorides decompose in water.

The diamine is a solid.

Dissolve 2 g of the diamine in 25 m. L of water.

Add 5 g of hydrated sodium carbonate.

Mix to dissolve. The reaction between the diamine and the acyl chloride is a condensation reaction which releases HCl. By making the solution alkaline, we will neutralise the HCl as it forms.

Prepare a clean beaker by greasing the sides with paraffin oil. This prevents the nylon from sticking to the glass.

Audio: Click on the movie to see what happens when the two solutions are mixed. (You may have to wait for it to finish loading. ) To prepare nylon the sebacoyl chloride solution in the organic solvent is placed into the beaker which has previously been treated with paraffin oil, and the diamine in water is then poured carefully on top of that solution. We finish up with a two-phase system where the amine and the sebacoyl chloride interact with each other and it is possible now with tweezers to pick up at the interface and to actually pull the nylon out of that interface. Now we can actually continue pull that almost indefinitely to produce a huge long continuous fibre of the nylon material.

By supporting the thread on test tubes, a very long thread can be pulled out of the beaker…

…a very long thread!