Polymers
- Polymers are large molecules built by linking 50 or more smaller molecules called monomers
- Polymers are known as macromolecules as they are relatively large compared with other molecules
- Each repeat unit is connected to the adjacent units via covalent bonds
- Some polymers contain just one type of unit
- Examples include poly(ethene) and poly(chloroethene), commonly known as PVC
- Others contain two or more different types of monomer units and which are called copolymers
- Examples include nylon and biological proteins
- Different linkages also exist, depending on the monomers and the type of polymerisation
- Examples of linkages are covalent bonds, amide links and ester links
Monomers Forming Polymers Diagram
Diagram showing how lots of monomers bond together to form a polymer
- Poly(ethene) is formed by the addition polymerisation of ethene monomers
- Addition polymerisation involves the addition of many monomers to make a long chained polymer
- In this case, many ethene monomers join together due to the carbon carbon double bond breaking
- Polymers are large molecules so their structures re shown as repeating units
- The polymer poly(ethene) can be represented by the repeating unit below
- n is the number of monomers in the polymer
Ethene forming poly(ethene) Diagram
Poly(ethene) is formed by addition polymerisation using ethene monomers
Properties of plastics
- Low weight
- Polymers are loosely packed so will be less dense and lighter than other materials such as metals
- Unreactive
- The addition polymers made from alkenes are saturated compounds because they do not contain double bonds and the main carbon chain is non-polar and will therefore are unreactive
- Water resistant
- Polymers are hydrophobic so they repel water instead of absorbing it
- Strong
- Polymers so are made up of many strong covalent bonds between the monomers
- These properties make plastics useful for packaging, construction, clothing and transportation
Natural and synthetic polymers
- Proteins, DNA and starch are examples of natural polymers
- Understanding the structure and function of natural polymers has been a major focus of biochemical research for the last 100 years and have contributed to the advancement of vaccines and medicines
DNA is an example of a natural polymer
DNA molecules form a three-dimensional structure known as a DNA double helix. It is made from four different monomers known as nucleotides which join together in different combinations to make a long strand
- Plastics are examples of synthetic polymers that have widespread uses due to their low weight, low reactivity, water resistance and strength
- They have become widely distributed across the world
- Their low reactivity means that they are non-biodegradable so will not break down naturally.
- The extensive accumulation of plastics in natural environments remains one of the most pressing environmental concerns
Nylon-6,6 is an example of a synthetic polymer
Nylon-6,6 is formed by condensation polymerisation
