Polymers (DP IB Chemistry)

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