1. Polymers
the formation of polymers from monomers including addition polymerisation of alkenes
the distinction between linear (thermoplastic) and cross-linked (thermosetting) polymers with reference to structure, bonding and properties including capacity to be recycled
the features of linear polymers designed for a particular purpose including the selection of a suitable monomer (structure and properties), chain length, degree of branching, percentage crystalline areas and addition of plasticisers
the advantages and disadvantages of the use of polymer materials

2. Polymers are made in nature...
A material consisting of big molecules that were made from smaller, simpler molecules.
Polymers are made in nature...
Explain: info

3. Explain: info It’s like joining up railway sleepers....
...or paper clips.
Each paper clip represents a small simple molecule, or monomer.
The paper clip chain is a model of the polymer.
Explain: info

4. Explain: info Most synthetic polymers are made from oil products.
Polymers are made up of long chains...
Explain: info

5. ...and by people. These are synthetic polymers.
Explain: info

6. Explain: info There are thousands of polymers.
Different polymers have different properties and different uses.
Explain: info

7. …some polymers are bouncy and stretchy…
Now, can we notice that…
…some polymers are bouncy and stretchy…
…some are sticky…
…and some are hard and strong
EXPLAIN
Explain: task OCR (B)

8. Polymers
The word “plastic” describes a property of a material which means that it can be readily molded into different shapes.
Polymers are often referred to as plastics. But not all polymers exhibit “plastic” properties.
All of the synthetic materials we call plastics are polymers.
Polymers are very large molecules that consist of many repeating units called monomers.
Monomers are small molecules. Most monomers contain the element carbon.
The chemical reactions that occur when polymers form can be modelled using plastic blocks that click together to form a long chain.
E.g. Casein is a polymer made up of many small molecules called amino acids. Amino acids are the monomers from which the casein polymer is made.

9. Boardworks AS Chemistry Alkenes
the formation of polymers from monomers including addition polymerisation of alkenes
Polyalkenes
The chemical reactions that join monomers together are known as polymerisation (polymer-forming) reactions.
Alkenes can undergo addition reactions with themselves to form a long chain polymer molecule. This reaction is addition polymerization.
Teacher notes
Students should be made aware that, in this instance, the R group can be either an alkyl group or a hydrogen atom.
The polymer can be represented by showing the repeating unit with square brackets around it. The n stands for a unspecified number of monomer units.

10. Polymerization of ethene
Boardworks AS Chemistry
Alkenes
Polymerization of ethene
Teacher notes
This is a simplified animation showing the polymerization of ethene, excluding the reaction mechanisms. Students could be asked to draw the mechanisms themselves.
See the ‘Halogenoalkanes’ presentation for more information about free radical reactions.

11. Naming Polymers
The prefix poly (meaning ‘many’) is often used when naming polymers.
For example, polyvinyl acetate (PVA) is a polymer made from the monomer known as vinyl acetate.

12. Boardworks AS Chemistry Alkenes
Which alkene?

13. Boardworks AS Chemistry Alkenes
Other polyalkenes
Propene undergoes addition polymerization to form polypropene:
Chloroethene undergoes addition polymerization to form polychloroethene:
Teacher notes
Students could be made aware that chloroethene is sometimes called vinyl chloride (an older name) and therefore polychlorethane is sometimes called polyvinylchloride (PVC).

14. Boardworks AS Chemistry Alkenes
LDPE and HDPE
The reaction conditions under which ethene polymerizes affect the structure and properties of the polyethene.
Low-density polythene (LDPE) is formed under a high pressure (1400 atm) and a temperature of about 170 °C.
These conditions cause a high level of branching, meaning that the polymer chains cannot pack tightly together.
High-density polythene (HDPE) is formed with a catalyst, a pressure of 2 atm and a temperature of about 70 °C.
Teacher notes
The catalyst used in the formation of HDPE is mixture of titanium(IV) chloride (TiCl4) and triethylaluminium (Al(CH2CH3)3). This is called Ziegler-Natta catalyst, after the scientists who discovered the process in the 1950s: Karl Ziegler and Giulio Natta.
Little branching occurs under these conditions, resulting in chains that can pack tightly together to create a denser material.

15. LDPE – Low Density Polyethene
Boardworks AS Chemistry
Alkenes
LDPE – Low Density Polyethene
LDPE is a soft, flexible and stretchy plastic, with a low melting point of about 120 C. It is used to make:
plastic bags
squeezable bottles, and general purpose containers and trays
other items that need to be soft and flexible, such as tubing.
LDPE has the recycling symbol ‘4’.
Photo credit: NatashaBo / shutterstock.com
Teacher notes
LDPE has excellent resistance to acid, bases, alcohols and esters
Recycling numbers were established in 1988 by the Society of the Plastics Industry (SPI) – a US organization.
The presence of branching means the molecules can not closely pack together. The dispersion forces between the forces are weaker because the molecules are further apart. It has a non crystalline and opaque appearance and does not conduct electricity.

16. Boardworks AS Chemistry Alkenes
HDPE – High Density Polyethene
HDPE is a tough and flexible plastic, with a relatively high melting point of about 130 °C. It is used to make:
containers such as milk and detergent bottles
rigid items such as folding tables, chairs and pipes.
HDPE has the recycling symbol ‘2’.
The lack of branches allows the molecules to pack closely together increasing the density and hardness. This makes it hard, more ordered with crystalline sections. It does not conduct electricity.
Photo credit: EuToch / shutterstock.com

17. Boardworks AS Chemistry Alkenes
Polypropene
Polypropene is a tough and flexible plastic, with a melting point of about 160 °C. It is used to make:
ropes, carpets, rugs and other textiles
medical, laboratory and kitchen items that need to withstand temperatures in autoclaves and dishwashers
Photo credit: Dole / shutterstock.com
Teacher notes
Polypropene is liable to damage from UV light, as well as oxidation at high temperatures. UV-absorbing chemicals and anti-oxidants are therefore commonly added during production.
certain bottles, buckets, containers and other items such as bottle tops and moulded fittings.
Polypropene has the recycling symbol ‘5’.

18. Thermoplastics polymers Thermosetting polymers
the distinction between linear (thermoplastic) and cross-linked (thermosetting) polymers with reference to structure, bonding and properties including capacity to be recycled
Polymers can be classified into 2 groups on the basis of their behaviour when heated.
Thermoplastics polymers
Thermosetting polymers

19. Linear (Thermoplastic) Polymers
the distinction between linear (thermoplastic) and cross-linked (thermosetting) polymers with reference to structure, bonding and properties including capacity to be recycled
Linear (Thermoplastic) Polymers
Thermoplastic polymers soften when they are heated.
They melt easily and can be molded into useful products when hot. So can be recycled.
Only have hydrogen bonds, dipole/dipole or dispersion forces between the long chains.
Eg: Polythene and PVC
The chains in a thermoplastic polymer are able to slide past each other when the polymer is heated, allowing the plastic to soften and melt.

20. Cross- linked (Thermosetting) Polymers
the distinction between linear (thermoplastic) and cross-linked (thermosetting) polymers with reference to structure, bonding and properties including capacity to be recycled
Cross- linked (Thermosetting) Polymers
Thermosetting polymers do not soften when they are heated, but char (blacken) instead. Can’t be recycled.
They are hard, rigid and sometimes brittle.
E.g. Bakelite and melamine.
In these polymers, the chains of monomer molecules are locked together firmly by covalent bonds between the chains, known as crosslinks.
Strong heating can break down their structure, leaving the black element carbon.
Used to make saucepan handles, bowling balls and shatter proof crockery.

21. Elastomers
Class of polymers that are formed when only occasional cross links ae present.
The chains can still move past each other when stretched but the cross links return the chains to their original positions once the force causing the stretching is released.
The cross links stop them from completely melting so they cant be recycled.
Rubber items such as gloves, bands etc are eg’s of elastomers.

22. Designing Polymers for a purpose
The development of new polymers has been motivated by the need to replace the existing material that are in short supply and to produce materials with improved physical and chemical properties.

23. Non-polar monomers
The properties of a polymer are mostly dependent on the monomer used to make them. Tetrafluoroethene is formed when all the Hydrogens on ethene are replaced with fluorine atoms. The polymer created from this addition polymerisation is called polytetrafluoroethene but is better known as Teflon. Teflon has properties very different from those made of polyethene.

24. Both Ethene and tetrafluoroethene molecules are non- polar, meaning that the intermolecular forces are present between polyethene and Teflon molecules are weak dispersion forces

25. Polar monomers
When a polymer is made from polar monomers the chains will be held together by stronger intermolecular forces like dipole-dipole interactions or hydrogen bonds.
Makes the polymer harder and more rigid.
Eg PVC : The carbon-chlorine bonds in the PVC molecule are polar and allow for dipole-dipole attractions to occur between the polymer chain.

26. Co-polymers and Conductive Polymers
When two different monomers alternate in the chain they create a co- polymer.
Polymers with alternating double and single bonds like polyethyne can become electrically conductive.
They are used in to make lighter polymer based circuits in biosensors.

27. the features of linear polymers designed for a particular purpose including the selection of a suitable monomer (structure and properties), chain length, degree of branching, percentage crystalline areas and addition of plasticisers
Crystallinity
When the chains are lined up in a regular arrangement they create crystalline regions- chains closer together, intermolecular forces are stronger, stronger material in general and opaque. Crystalline regions in a polymer prevent the transmission of light through the material, making it appear opaque (cloudy) and light can not travel directly through it.
Amorphous regions are where the chains are randomly tangled and cannot pack closely together- less rigid, weaker and transparent.
Increasing the percentage of polymer that is crystalline, rather than amorphous, influences the properties of the polymer. Making it stronger and less flexible. It would also make the polymer less transparent as the crystalline regions scatter the light.

28. Chain Length and extent of branching
the features of linear polymers designed for a particular purpose including the selection of a suitable monomer (structure and properties), chain length, degree of branching, percentage crystalline areas and addition of plasticisers
Chain Length and extent of branching
If the chain length is extremely long then dispersion forces between chains are much stronger and make the material tough- used for bullet proof vests and artificial hip joints.
Few branches = molecules closely packed together, high percentage of crystallinity (95%).
Longer, more frequent and random branches = soft, flexible, transparent and lower crystallinity (65%).

29. Side Groups- position and size
the features of linear polymers designed for a particular purpose including the selection of a suitable monomer (structure and properties), chain length, degree of branching, percentage crystalline areas and addition of plasticisers
Side Groups- position and size
The way the side groups are arranged along the polymer chain effects the properties and uses of the polymer. The way the methyl side group is arranged along the polymer chain in polypropene has a significant effect on the properties and uses of this polymer.
Isotatic polypropene has all the side groups on one side of the polymer chain. This allows the crystalline regions to form, and significant attractive forces between the chains.
Atacic polypropene has the side groups randomly distributed. This prevents the chains from stacking well together and forming crystalline regions. It is very soft and has limited usefulness.
Sydiotactic polypropene has the side groups on regularly alternating sides of the polymer chain. This allows for good packing and the material is highly crystalline.

30. Side groups
Bulky side groups make it harder for chains to slide over each other or stack closely together = prevents crystalline regions so amorphous material is produced instead which is transparent.

31. the features of linear polymers designed for a particular purpose including the selection of a suitable monomer (structure and properties), chain length, degree of branching, percentage crystalline areas and addition of plasticisers
Additives
Pigments (for colour), UV stabilisers (prevents deterioration form sunlight), Flame retardants and Plasticisers (makes materials softer and more flexible because they weaken intermolecular forces between polymer chains).
Plasticisers
Plasticisers are small molecules that can be added to polymers during their manufacture. The polymer molecules are forced slightly apart, weakening the forces between the chains and making the material softer and more flexible. PVC benefits from addition of plasticier molecules as pure PVC is quite rigid due to the polymer chain being held in strongly together due to the polar carbon-chloride bond. When a plasticizer is introduced between the chains, the chains can slide past each other, making the polymer softer and flexible.

32. the advantages and disadvantages of the use of polymer materials
Pros Vs Cons
Most polymers are made from non-renewable resources and are not biodegradable.

33. Advantages and Disadvantages of Polymers
The disposal of the waste polymer material is a serious issue in our society.
Worldwide, nearly 3 millions tonnes of plastic are used to bottle water every year.
Plastics are durable, chemically resistant and lightweight. These properties make plastics very useful, but these properties also mean that they cause a serious environmental issue.
It is estimated that over 13,000 pieces of plastic litter are floating on every square kilometre of ocean surface.

34. Biodegradable Plastics
Biodegradable plastics are made from renewable plant materials such as corn and starch.
Another approach involves including additives, such as transition metals, in the polymers used to make food wrapping and shopping bags. These additives promote degradation of polymer chains to smaller, biodegradable compounds over time.

35. Recycling Plastics There are two ways of recycling plastics.
Reprocessing involves shredding, melting and reshaping used plastic into new, clean products. This method can only be used with thermoplastic polymers. Repossessed polyethene can be used for manufacturing carry bags, rubbish bins and liners and bottle crates.
The other method of plastic recycling involves depolymerisation, in which polymers are broken down into monomers. These monomers are then used in the production of new polymers. This requires a large amount of energy and the yield is usually low making this less economically viable.