Year 11 Chemistry: Chapter 8:~ Polymers
8.6 Polymers: long-chain molecules
Cotton, wool and silk are some of the naturally occurring ______. There are many polymers that have been developed by chemists, these are ______polymers. Some examples are cling film, clothing, domestic appliances, cars, plumbing materials and sporting equipment.
Polymers, not plastics
For chemists the word, ‘plastic’, describes a property of a material. A substance is described as being plastic if it can be ______into different shapes readily.
Malleable and ductile are terms used to describe the ______properties of metals. Liquids and gases are infinitely plastic as they take the ______of any container.
Many polymers are plastic materials, as they can be shaped or moulded. Some polymers are not plastic materials, they are brittle and cannot be reshaped, some examples are light switches and power points.
8.7 Polymers: what are they?
Polymers are very large covalent molecular substances containing tens of thousands of atoms, They are formed by joining together a great many small molecules, called ______(single unit) in a process called ______.
Two main types of polymerisation processes:
J Addition polymerisation
J Condensation polymerisation
The polymers formed through addition polymerisation often have the name of the monomer(s) included in the name of the polymer. Example: Polyethene – is formed from the monomer ______, PVC, polyvinyl chloride is formed from the monomer ______. Some condensation polymers are named after the chemical bond formed between the monomers, for example: polyesters monomers are joined together by an ______functional group.
Addition polymers
Covalent bonds form between the monomer molecules to produce a polymer molecule.
*Draw diagram 8.28
Suitable monomers for addition polymerisation are ______(saturated or unsaturated) molecules. The double bond splits between the two carbon atoms and reacts forming new covalent bonds.
Polyethene: an addition polymer
Polyethene was discovered by accident in England in the 1930’s. It was first used to make cables and insulate radar aerials during World War II.
In the process of addition polymerisation , all of the atoms present in the monomer molecules are present in the polymer molecule. The monomers are simply added.
In any particular sample of polyethene, the sizes of the molecules will vary,
Polyethene is a thermoplastic polymer. This means that it will melt when heated and can be reshaped. This is because of the bonds between the non-polar chains are weak ______forces. The strong covalent bonds remain unchanged.
There are two different types of polyethene.
J High-density polyethene (HDPE): used for pipes, buckets, toys, containers and freezer bags. Polymerisation of ethene: atmosphere pressure, using a metal oxide catalyst and temperature of 310°C. Produce very few and small branches, making it high density.
*Draw figure 8.29
J Low-density polyethene (LDPE): used for cling films, garbage bags, squeeze bottles, carry bags and insulating cables. Polymerisation of ethene: high pressure (1000-3000 atm), using oxygen to initiate the reaction and temperature of 300°C. Producing many branches making it low density.
*Draw figure 8.29
*Look at table 8.9
Structure, Properties and Applications
Two very important properties of polymers are ______strength and ______temperature.
Define:
J Tensile strength: ______
______
J Softening Point: ______
______
In thermo______, both tensile strength and softening point are affected by:
J
Another factor that affects the properties of a polymer is ______.
Define:
J cross-links:
The more cross-links the more rigid the polymer. Polymers with extensive cross-links are called ______. They do not soften on heating, when there is sufficient heat they will char.
Degree of branching
Atoms in chains that are arranged regularly create crystalline regions. The more regions of crystallinity, the greater the degree of light scattering and the less transparent the polymer. That is why ______is frequently ______transparent while HDPE is not.
Nature of side groups
Polystrene (draw the structural formula of the monomer and polymer from pg 156)
The bulky ring (C6H6) prevents chains from stacking close together and forming crystalline regions. As a result, polystrene is amporphous ( ______) and transparent and has a low density. It is quite brittle and gives a metallic ring. The bulky ring makes it difficult for the chains to silde over each other.
Pure polystrene is too brittle for many used so it is frequently modified by the ______of ______to produce ‘’ ______’ eg bicycle helmets. Polystrene foam is produced by blowing a _____ , pentane or ______, through melted polystrene beads. What other properties can be modified? ______
______
Arrangement of side groups
Example Polypropene: (draw the structural formula from pg 158)
J Atactic polypropene: Groups are ______disturbed. Properties: soft and greasy.
J Isotactic polypropene: ______chains. Are used to produce babies bottles that can be sterlised in hot water without softening.
Amounts of cross-links
Extensive cross-linking
Thermsets are brittle and cannot be reformed. They ______when heated. Thermosets will shatter when impacted.
Occasional cross-linking
Elastomers are materials that will regain their ______shape after being stretched or pulled out of shape, this is known as ______.
Rubber is one material which is cross-linked during manufacture to give is elastic properties. This process is known as ______. Charles Goodyear discovered elastic properties by accident in 1843. Nowadays chemists carefully add carefully controlled amounts of sulfur to rubber in the form of unlinked polymer chains and heat. Sulfur atoms react with the ______double bonds in the chains, forming ______made up of a number of sulfur atoms.
If a small amount of sulfur is used the polymer becomes more elastic. If large amounts of sulfur are added, more extensive cross-linking results in a more rigid material. Elasticity varies with the ______of ______between polymer chains.
*Draw diagram 8.36 on pg 159.
Customised polymers
Define:
J Copolymers:
What properties can be modified by customising polymers:
J
How can the polymers be altered:
J
Recycling plastics
Australians consume more than ______tonnes of plastic every year. This includes more than 40 different plastics. The disposal of waste plastic material is a serious issue to our society.
*Write down the 6 polymer types (just the ‘polymer type’ column) in table 8.10.
Read: pg 161 ‘ Buckyballs and nanotubes’ – this will help you with your research assignment.
QUESTIONS: complete all questions for Chapter 8 in your timeline.