polymers

• a polymer is a large molecule made from lots of small molecules, called monomers, this process is called polymerisation
• a polymer is a substance of high average relative molecular mass made up of small repeating units
• alkenes can combine to make polymers in a polymerisation reaction, in this reaction many small molecules (monomers) join to create a very large molecule (polymer)
• ethene molecules combine in a polymerisation reaction, poly(ethene) is made when one of the bonds in the double bond, breaks open and another ethene molecules adds on, this process is repeated forming a long chain - this is called addition polymerisation
• addition polymerisation

  
• any alkene can be used as a monomer to create a polymer due to the C=C bond

  • propene -> poly(propene)
  • chloroethene -> poly(chloroethene) (PVC)
  • tetrafluoroethene -> poly(tetrafluoroethene)(PTFE)
• structure of a monomer from the structure of an addition polymer and vice versa

  • monomer is the same as the repeated unit, just replace the C-C with C=C and remove the brackets and "n"
  • polymer is the same as the monomer, just replace the C=C with C-C , add brackets and "n"
• poly(ethene)

  properties : flexible, cheap, good insulators

  uses : plastic bags, bottles, cling film
• poly(propene)

  properties : flexible, does not shatter, strong

  uses : buckets, bowls, ropes, crates
• poly(chloroethene), PVC

  properties : tough, good insulator, can be hard or flexible

  uses : windows, frames, gutters, pipes
• poly(tetrafluoroethene) PTFE

  properties : tough, slippery

  uses : non-stick coatings, stain proofing, clothing, carpets
• why polyesters are condensation polymers

  polyesters are synthetic polymers made by condensation polymerisation

  • in condensation polymerisation, a small molecule is formed as a by-product each time a bond is formed between two monomers
  • alcohol and carboxylic acid functional groups react, losing a small molecule – water
  • this is an ester – therefore a polyester is a lot of these monomers (esters)
• how a polyester is formed when a monomer molecule containing two carboxylic acid groups is reacted with a monomer molecule containing two alcohol groups

  • the dicarboxylic acid looses the OH group off of each COOH group
  • the di-alcohol loses the H off each OH group
  • remaining molecules join together to make a polyester
• how a molecule of water is formed each time an ester link is formed

  a water molecule is formed each time an ester link is formed by the OH and H groups combine to make H2O
• some problems associated with polymers

  • availability of starting materials
  • persistence in landfill sites, due to non-biodegradability
  • gases produced during disposal by combustion
  • requirement to sort polymers so that they can be melted and reformed into a new product
• recycling polymers


  advantages

  • reuse waste material - better to the environment than burning or putting them in land fields
  • saves crude oil - a finite resource
  • more economically viable instead of making more polymers

  disadvantages

  • difficult and expensive to first separate the different polymers (need to be sorted into types before recycling)
• polymers are formed by the joining up of many small molecules with strong covalent bonds, the presence of strong covalent bonds make polymers unreactive and chemically inert, hence, they are usually non-biodegradable, when non-biodegradable polymers such as plastics are thrown at landfills, they cause landfills to fill up quickly as decomposers are unable to break them down
• polymers also release carbon dioxide, which is a greenhouse gas when they are decomposed via combustion. This can lead to climate change. polymers which contain chlorine such as PVC releases toxic hydrogen chloride when burned. If polymers are incinerated by incomplete combustion, carbon monoxide may be released which is harmful to the respiratory system
• DNA is a polymer made from four different monomers called nucleotides
• starch is a polymer based on sugars
• proteins are polymers based on amino acids