13.5 Polymerisation In Alkenes
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What are polymers?
Extremely large molecules formed from many thousands of repeat units of small molecules (monomers)
What kind of polymerisation do unsaturated ALKENE molecules undergo?
Addition polymerisation
What determines the properties of a polymer?
The monomers used
What are the conditions for industrial polymerisation?
High temperature, high pressure, presence of catalysts
Do addition polymers have high or low molecular masses?
High
What are the rules for drawing a repeat unit?
• Repeating unit is always written in square brackets • After the bracket, you place the letter “n” • Repeat units are only ever a maximum of 2 carbons wide • If there is another monomer unit, you place the letter “m” behind
What is a repeat unit?
The specific arrangement of atoms in the polymer molecule that repeats over and over again
What can polychloroethene be prepared to make?
Polymers that are either flexible or rigid
What are the environmental concerns surrounding polymers?
• Unreactive, so difficult to dispose of/break down • Many alkane-based polymers are non-biodegradable
How are polymers recycled?
Polymers are sorted, chopped into flakes, washed, dried, melted, then cut into pellets and used to make new products
Why is recycling PVC dangerous?
• Because of the high chlorine content, and the range of additives present in the polymer • When burnt, PVC releases hydrogen chloride (a corrosive gas), and other toxic pollutants
How do we recycle PVC?
Use solvents to grind the polymer, and high-grade PVC is recovered by precipitation from the solvent
Why are some polymers difficult to recycle?
Because they have a high stored energy value
What can be done with waste polymers to give them use?
Can be incinerated to produce heat, generating steam to drive a turbine producing electricity.
What is feedstock recycling?
The chemical and thermal process that can reclaim monomers, gases, or oil from waste polymers
What is a major advantage of feedstock recycling?
It can handle unsorted and unwashed polymers
What are bioplastics?
Plastics produced from biological components, such as plant starch, cellulose, plant oil, protein
How are biodegradable polymers degraded?
Broken down by organisms into water, carbon dioxide, and biological components
What are photo-degradable polymers?
Polymers that contain bonds that are weakened by absorbing light, to start the degradation
How can manufacturers claim that using plant material to make polymers is carbon neutral?
The amount of CO2 released when the polymer degrades is equal to the amount of CO2 taken in by the plant.
Why is it ultimately untrue that using plant material for polymers is carbon neutral?
Because more CO2 is produced when manufacturing the polymer
What is one of the toxic waste gases produced when PVC is combusted?
Hydrogen Chloride