C15.3 The properties of polymers
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What does the property of a polymer depend on?
The monomers used to make it The conditions chose to carry out the reaction
What are the different types of polyethene?
High density and low density
How is LD polyethene made?
Very high pressures and traces of oxygen The polymer chains are randomly branched and cannot pack closely together - hence its lower density
How is HD polyethene made?
Using a catalyst at 50 degrees and slightly raised pressure This is made up of straighter poly(then) chains They can pack more closely together than branched chains hence its higher density
What is the advantage of using HD polyethene over LD?
Has a higher softening temperature and is stronger than LD
What are thermosoftening polymers?
Polymers that can be manipulated into different shapes when they are hot, and the shape sets when it cools Made up of individual polymer chains that are tangled together - relatively easy to seperate
What are thermosetting polymers?
Polymers that do no melt when we heat them These have strong covalent bonds forming cross-links between their polymer chains
What are the benefits of cross linking covalent bonds?
Makes thermosetting polymer chains heat-resistant and rigid
How do thermosoftening polymers work?
The forces between the polymer chains are weak When you heat the polymer - these weak intermolecular forces are broken - the polymer becomes soft When the polymer cools down - the intermolecular forces bring the polymer molecules back together - hardens again
How do thermosetting polymers work?
The monomers make covalent bonds between the polymer chains when they are first heated to shape them The covalent bonds are strong enough to stop the polymer from softening The cross-links between the chains do not allow them to separate The polymer wont soften