Edexcel GCSE Chemistry: Topic 9 - Polymers

Definition of Polymers

• Polymer: A substance with a high average relative molecular mass made from small repeating units known as monomers.

Addition Polymerisation

• Polymerisation Reaction of Ethene:

  • Ethene molecules can combine in a polymerisation reaction to form poly(ethene).

  • Key Characteristics:

  • The repeat unit in the polymer has the same atoms as the monomer since no other molecules are produced.

  • Example: Ethene (monomer) joins to form poly(ethene) (polymer).

• Alkenes in Polymer Synthesis:

  • Any alkene can be used to create a polymer due to the presence of the carbon-carbon double bond (C=C).

• Common Addition Polymers:

  • Poly(propene)

  • Poly(chloroethene) (PVC)

  • Poly(tetrafluoroethene) (PTFE)

Characteristics of Addition Polymers

• Structure Deduction:

  • To deduce the monomer structure from the addition polymer structure, the repeat unit can be recognized as the monomer, with the C=C bond represented where the C-C bond was located, and brackets along with the “n” notation are removed.

Properties and Uses of Common Polymers

• Poly(ethene):

  • Properties:

  • Flexible

  • Cheap

  • Electrical insulator

  • Uses:

  • Plastic bags

  • Bottles

  • Coating on electrical wires

• Poly(propene):

  • Properties:

  • Flexible

  • Strong

  • Uses:

  • Buckets

  • Crates

• Poly(chloroethene) (PVC):

  • Properties:

  • Tough

  • Cheap

  • Long lasting

  • Uses:

  • Window frames

• PTFE:

  • Properties:

  • Tough

  • Non-stick

  • Uses:

  • Non-stick coating on pans

Condensation Polymerisation

• Polyesters:

  • Reason for Condensation Polymerisation:

  • In condensation polymerisation, a small molecule (e.g., water) is formed as a by-product when forming bonds between monomers.

  • Reaction involves alcohol and carboxylic acid functional groups.

• Formation of Polyester:

  • When a dicarboxylic acid reacts with a di-alcohol, both lose atoms that form water.

  • The excess parts then combine to create a polyester.

• Water Formation:

  • Each time an ester link is formed, an OH group from the acid and an H from the alcohol join together to form a water molecule (H_2O).

Environmental Considerations of Polymers

• Non-biodegradability of Polymers:

  • Strong covalent bonds within polymers render them unreactive and chemically inert, making disposal a concern as they do not decompose.

• Impact on Landfills:

  • Non-biodegradable polymers contribute significantly to landfill expansion since decomposers fail to break them down.

• Greenhouse Gas Emissions:

  • Decomposing polymers via combustion can release carbon dioxide, a greenhouse gas responsible for climate change.

• Toxic Emissions from Combustion:

  • Burning PVC releases toxic hydrogen chloride gas.

  • Incomplete combustion can lead to the release of carbon monoxide, which is harmful to the respiratory system.

Challenges Associated with Polymers

• Evaluation of Recycling Polymers:

  • Advantages:

  • Allows for the reuse of waste materials, which is more environmentally friendly than disposal methods like burning or landfill storage.

  • Conserves finite resources, such as crude oil.

  • More cost-effective than producing new polymers from scratch.

  • Disadvantages:

  • Separation of different types of polymers can be complex and expensive, requiring precise sorting before recycling can occur.

Biological Polymers

• DNA:

  • A polymer formed from four different monomers called nucleotides (specific names of nucleotides not essential for understanding).

• Starch:

  • A polymer based on sugars, functioning as an essential energy source.

• Proteins:

  • Structural and functional polymers based on amino acids, vital for numerous biological roles in living organisms.