4.1.3 Polymerisation of alkenes Flashcards
define polymer
A large molecule formed from many thousands of repeating units of smaller molecules known as monomers
define monomer
A small molecule that combinds with many other identical small molecules (monomers) to form a polymer
define and explain addition polymerisation
Addition polymerisation is the formation of a very long molecular chain, by repeating addition reactions of many unsaturated alkenes molecules (monomers). Which produces long saturated chains. This happens when the C=C on one alkene monomer reacts with the C⁺ on another alkene monomer and the process continues.
Addition polymers have high molecular masses
What impacts the propertites of a polymer
The monomer used to form it
What are the types of polymers (that we study)
- addition polymers
- synthetic polymers - these are usually named afterthe monomer that reacts to form their giant molecules, prefixed by ‘poly’
What are the conditions for industrial polymerisation
It is carried out at high temperaturess and high pressure using a catalyst
Define repeat unit
Def. A repeat unit is the specific arrangement of atoms in the polymer molecule that repeats over and over again.
The repeat unit is always written in square brackets.
After the bracket an n is placed to show that there is a large number of repeats.
There are bond lines drawn through the brackets from the Carbons.
What is the general equation for addition polymers
……..A…….X………………A….X
……..|…….|………………|….|
n……C = C…….→ ..— C - C —
……..|…….|………………|….|
……..B…….Y………………B….Y
The saturated monomer above (right) would all be enclosed in square brackets with the one sided bonds sticking through the brackets and then in the bottom right next to the closing square bracket would be an n to represent a large number repeating AND to balance the equation.
If asked to show 3 repeating units then: remove the n and the square brackets keep the one ended bonds and show the 3 repeatign units.
Describe poly(ethene)
Poly(ethene) is made by heating a large number of ethene monomers at a high pressure.
It is one of the most commonly used polymers - supermarket bags, toys, bottles, pipes.
There are two main types HDPE and LDPE - High density and low density poly(ethene).
HDPE has linear chains which gives the plastic strength, so it is often used for toys, pipes, bottles.
LDPE has branched chains which doesnt give as much strength to the plastic but does make it flexible so it is often used for plastic films and plastic bags.
List some common polymers
The structural formula shows their monomer
- poly(propene) → CH₂=CHCH₃ → toys, plastic bags
- poly(Chloroethene) PVC → CH₂=CHCl → pipes, bottles, flooring
- poly(tetrsfluoroethene) PTFE, teflon → CF₂=CF₂ → coating for non-stick pans, cable insulation
Why is plastic ideal for food storage and why is this bad
Plastic is chemically unreactive and non-biodegradable which makes it ideal for food storage but due to it not breaking down plastic waste has serious environmental effects, such as killing marine life
what are the methods for processing waste polymers
- Combustion to provide energy
- organic feedstock production
- recycling
Explain combustion to provide energy as a method for processing waste polymers
Plastics are mainly hydrocarbons, so they are good fuels.
The plastics that can’t be recycled or reused are burned for fuel so that the energy from their store is obtained and used.
also known as incineration to provide energy.
What is a disadvantage of combustion to provide energy as a method for processing waste polymers
Incomplete combustion of the plastics would produce carbon monoxide (CO), which is toxic. Additionally plastics such as PVC (chlorinated polymers) produce HCl when burned, which is a corrosive gas and causes acid rain.
However HCl can be removed by reacting the gases with a solid base of metal oxide or carbonate
What is an advantage of combustion to provide energy as a method for processing waste polymers
Plastic waste that is burned for fuel is not sent to landfill where it takes up a lot of space.
