Condensation Polymers (OCR Gateway GCSE Chemistry)

• Condensation polymers are formed when two different monomers are linked together with the removal of a small molecule, usually water
• This is a key difference between condensation polymers and addition polymers:
  • Addition polymerisation forms the polymer molecule only
  • Condensation polymerisation forms the polymer molecule and one water molecule per linkage

• The monomers have two functional groups present, one on each end, such as diols (an alcohol each end) or dicarboxylic acids (a carboxylic acid each end)
• The functional groups at the ends of one monomer react with the functional group on the end of the other monomer, in so doing creating long chains of alternating monomers, forming an A-B-A-B pattern in the polymer
• It is possible to have monomers with one of each functional group; such as an alcohol one end and a carboxylic acid at the other end (A-A type polymers, such as proteins from amino acids)
• Most synthetic polyesters are formed from two different monomers and produce water
• There are two main types of synthetic condensation polymers; polyesters and polyamides

Forming Polyesters

• Polyesters are made from dicarboxylic acid monomers (a carboxylic with a -COOH group at either end) and diols (an alcohol with an -OH group at either end)
• Each -COOH group reacts with the -OH group on a diol on another monomer
• An ester link, –COO–, is formed with the subsequent loss of one water molecule per link, formed from the combination of a hydrogen ion (proton) (H⁺) and a hydroxide ion (OH^–)
• Terylene is an example of a polyester

The condensation reaction in which the polyester terylene is produced

• The structure of terylene can be represented by drawing out the polymer using boxes to represent the carbon chains
• This can be done for all polyesters

Diagram showing a section of a polyester 

Forming Polyamides

• Polyamides are made from dicarboxylic acid monomers (a carboxylic with a -COOH group at either end) and diamines (an amine with an -NH₂ group at either end)
• Each -COOH group reacts with another -NH₂ group on another monomer
• An amide link, –CONH–, is formed with the subsequent loss of one water molecule per link, formed from the combination of a hydrogen ion (proton) (H⁺) and a hydroxide ion (OH^–)
• Nylon is an example of a polyamide

The condensation reaction in which the polyamide, nylon is produced

• The structure of polyamides can be represented by drawing out the polymer using boxes to represent the carbon chains

Diagram showing a section of a polyamide

Health & Safety Aspects

• The solutions used here are hazardous and contain toxic materials and solvents so care should be taken when handling and disposing of them
• Small quantities are used to minimise the risks associated with these substances

Making Nylon in the Lab

• Two solutions are made, one containing 1,6-diminohexane dissolved in water, and a second solution containing decanedioyl dichloride dissolved in cyclohexane
• 5 cm³ of aqueous 1,6-diaminohexane solution is poured into a 25 cm³ beaker
• 5cm³ of decanedioyl dichloride solution is added carefully on top of the first solution so that mixing is minimised
• The decanedioyl dichloride solution will float on top of the aqueous solution without mixing
• A white coloured film of nylon will form at the interface
• A little of the film can be picked up with a pair of tweezers and wrapped around a glass rod
• As the glass rod is rotated a 'rope' of nylon is extracted from the beaker

The nylon rope trick

• The two monomers contain a reactive group at each end of the molecules
• These groups react together and join up to form long chains, rather like a bead necklace with alternating coloured beads
• The result is nylon, which is actually named after the two cities where it was first discovered- New York and London!
• This particular type of nylon is called nylon 6,10, which refers to the length of the two monomer pieces containing links that are 6 carbons long (from the diamine) and 10 carbons long (from the diacyl chloride), respectively