polymers

Addition Polymers

· formed by addition reactions of monomers containing C=C

· monomers are the small subunits of a chain

· polymers are long chains of monomers

· an example of an addition polymer is polyethene (commonly polyethylene)

· addition polymers are commonly used as plastics

· double bonds are replaced with single bonds to neighbouring carbons

· other common examples of addition polymers include polypropylene, polyvinyl chloride (PVC), and polystyrene

Condensation Polymers

· monomers are not identical in condensation polymers

· pairs are called dimmers because they form the pattern: ABABABABABABABAB

· condensation polymers are used in fabrics

· there are two main groups of condensation polymers

· polyesters are formed by the reaction between a carboxylic acid and an alcohol

· the reaction forms water and links the two monomers

· polyamides are formed by the reaction between a carboxylic acid and amines

· this reaction also forms water

· the presence of oxygen allows for hydrogen bonding and/or dipole force between chains

· allows for strong but flexible attraction

Proteins

· make up about half of the dry mass of our bodies

· perform various functions including enzymes, structure, hormones etc.

· monomers of proteins are amino acids

· contain a central carbon that is attached to an amine group, a carboxylic acid group, a hydrogen and a functional side chain

· there are 20 different amino acids each with a different functional side chain

· the carboxylic acid of one amino acid has a condensation reaction with the amine of the neighbouring amino acid to form a polyamide

· this bond is commonly called a peptide bond proteins are also known as polypeptides

Attraction Between Chains

· All polymers are large molecules and as a result experience high levels of London forces

· given the size of the chains these forces are strong enough to hold the chains together

· weak enough to allow flexibility

· broken when heated (why plastic melts)

· polymers with different sidechains can have higher attraction (e.g. Condensation polymers have O or N to cause hydrogen-bonding/dipole attractions)

· polymers can also be strengthened with crosslinking

· these are atoms that periodically bond to both adjacent chains

· crosslinked plastics are not softened by heating and are called thermoset polymers

· polymers that are held together by London forces only are called thermoplastics

· Thermoplastics are more likely to degrade during heating or stress

· Polymers are created with different properties to do different jobs

· Fabrics are made from polymers that are flexible, but strong enough not to melt in the sun

· Cookware is coated in heat resistant polymers that will not melt into food