14.3 Addition polymers Flashcards
What are polymers
Large molecules built up from small monomers
They occur naturally everywhere: Starch, proteins, DNA
What are addition polymers
They are made from monomers with a double carbon carbon bond (alkenes)
Addition polymers are made from monomers based on ethene: C2H4
What happens during addition polymerisation
Eg in ethene
. The double carbon-carbon bond opens and the monomers bond together to form a backbone of carbon atoms
Because each carbon now has one lone pair which it can use to covalently bond to another molecule
What is the name of the polymer of ethene
What is the name of the polymer of phenylethene, or another name for it is styrene
Poly(ethene)
Poly(phenylethene)
or polystyrene
How do you identify the monomers used to make an addition polymer
An addition polymer has a backbone of carbon atoms, and the monomer must contain at least two carbons, so there can be a carbon-carbon double bond
What are plasticisers
What do they do
The properties of polymer materials are modified by using additives such as plasticisers
These are small molecules between the polymer chain forcing them apart and allowing them to slide across each other
So it can make rigid materials quite flexible
Why are polyalkenes not biodegradable
. Alkanes have strong non polar C-C and C-H bonds so are very unreactive
Long saturated carbon chain
This means they are not attacked by biological agents eg enzymes, so are not biodegradable
How is low density poly-ethene made
It can be made by polymerising ethene
At high pressure and high temperature via a free radical mechanism
This makes a highly branched polymer, so the chains don’t pack together tightly
So the product is flexible,
How is high density polyethene made
Made at medium temperature, slightly above room temp
. Ziegler-Natta catalyst
. It results in a polymer with much less chain branching so the chains can pack more closely together
. So material is more dense, melting point is higher
What is mechanical recycling
What are the steps to it
Simplest form of recycling
. Separate out different types of plastics
. Then wash them
. Once they are sorted they may be ground up into small pellets
. Melt and remould these
What is feedstock recycling
. Heat the plastics to a temperature that will break the polymer bonds and produce monomers
. These can be used to make new plastics
What is the problem with recycling plastics
Eg with poly(propene), it is thermoplastic polymer
So it will soften when heated so can be melted and re-used
However this can only be done a limited amount of times because each heating causes some of the chains to break and become shorter
