Addition Polymers

• What are polymers?

  Large molecules that are made up of many small monomers
• What are addition polymers?

  Polymers that are made from alkene monomers

  When the monomers polymerise, the double bond opens so the polymer is now an alkane
• What is the reactivity of addition polymers?

  Unreactive

  Alkane is formed as the double bond opens
• How can polymers be modified?

  Plasticisers

  Small molecules that get between the polymer chains, forcing them apart and allowing them to slide across each other
• Are polymers biodegradable?

  Polymers are not biodegradable

  The polymers are alkanes, which are very unreactive molecules so they are not attacked by biological agents, such as enzymes
• How is low density poly(ethene) made?

  Polymerising ethene at high temperatures and high pressures via a free-radical mechanism
• What are the properties of low density poly(ethene)?

  Branched chains - don’t pack together well

  Flexible

  Low melting point

  Low density

  Uses: plastic bags, insulation for electrical cables, sheeting
• How is high density poly(ethene) made?

  Polymerising ethene at low temperatures and low pressures greater than room conditions, using a Ziegler-Natta catalyst
• What are the properties of high density poly(ethene)?

  Straight chains - pack together well

  High melting point

  High density

  Uses: milk crates, buckets, bottles
• What is mechanical recycling?

  Plastics are separated into different types which are then washed and ground up into small pellets that can be melted or remoulded
• What is feedstock recycling?

  Plastics are heated to a temperature that will break the polymer bonds and produce monomers, which can be used to make new plastics
• What are the problems with recycling?

  When plastics are heated and reused, the chains become shorter, degrading the plastic’s properties