Polyesters - Higher
Long molecules (such as nylon, Kevlar or polyester) produced during condensation polymerisation. form in a different way to Large molecule formed in addition reactions between unsaturated monomer molecules. like poly(ethene). Instead of just one A substance formed in a chemical reaction. forming (the A large molecule formed from many identical smaller molecules known as monomers.A collection of two or more atoms held together by chemical bonds.), two products form:
- a polymer molecule
- a small molecule, often water
Condensation polymer made from two types of monomer, one with two –OH groups and one with two –COOH groups. are condensation polymers.
Forming esters
An A type of organic compound formed in the reaction between an alcohol and a carboxylic acid. forms when an An organic compound containing a hydroxyl group, -OH. The 'alcohol' in alcoholic drinks is ethanol, produced by the fermentation of sugars and found in wines, spirits and beers. reacts with a A homologous series of compounds that contain the carboxyl functional group, -COOH.. For example:
ethanol + ethanoic acid → ethyl ethanoate + water
CH3CH2OH + CH3COOH → CH3COOCH2CH3 + H2O
Ethyl ethanoate is an ester. Notice that one water molecule forms when one ester molecule forms.
Forming polyesters
A polyester forms from two different Small molecule, usually containing a C=C bond, that can join end to end with other monomers to form a polymer molecule.:
- a ‘dicarboxylic acid’ which contains two carboxylic acid groups, -COOH
- a ‘diol’ which contains two alcohol groups, -OH
For example, PET is a polyester made from terephthalic acid and ethane-1,2-diol. It is used to make drinks bottles and fleece clothing.
Notice that:
- both ends of each monomer molecule can react with another monomer molecule
- one molecule of water is formed every time an ester link is formed
- one A part of a polymer that would make a complete polymer molecule if many of them were joined end to end. is made from two different monomer molecules
The monomers and polymer can be represented by simplified ‘block diagrams’. In these diagrams, only the functional groups are shown in detail. The rest of the molecule is shown with the symbol R or as a shaded block.
