Condensation Polymers

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Program Support Notes

Grades 10 - College Investigating Polymers Series 20mins Condensation Polymers

Produced by Rod Rees and Associates for Video Education Australasia

Suitable for:

Chemistry

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Overview of Program

This particular program is the 2nd of a series on the preparation and properties of polymers and focuses on the condensation process. The content assumes that students have a basic knowledge of molecular structure and covalent bonding. It is well presented with a wide range of condensation polymers displayed with good graphics demonstrating how the process occurs.

The programs begins by showing a wide range of plastics that are used in society from plastic bottles, hot air balloons to roller blades, stating that these are produced in a chemical factory not like the natural polymers of cotton and wool. By investigating the molecular structure, the wide range of properties can be explained.

The student is reintroduced to terms such as polymer and monomer and the addition process (preparation of polyethene) is explained so that the difference between the condensation process is clear. Addition involves the breaking of a double bond to link many monomers together and no by-product is produced.

Condensation polymerisation is introduced using the formation of nylon. Instead of breaking double bonds, the monomers contain functional groups which react together. As the monomers collide, some of the covalent bonds rearrange to form a link and a by-product such as water is produced. Nylon is produced from co-polymers (i.e. 2 different monomers) containing the carboxyl and amine functional groups which react with each other to form the links.

The difference between addition and the condensation process is clearly explained using molecular models. With the addition process, the functional groups are not involved in the actual formation of the polymer chain where as in the condensation process, it is the actual atoms in the functional group, such as carbon and nitrogen, which link the monomers and become part of the polymer chain.

Bonding between the polymer chains determines the properties of the plastic. Molecular models are used to explain the differences between dipole-dipole interactions of nylon (Kevlar) and the dispersion forces of polystyrene, with the nylon having a much higher melting point because the dipole-dipole forces are stronger. The program features the wide variety of uses of tough Kevlar from tennis racket strings to the wings of some aircraft.

Another way polymers can be classified is by whether they melt or char on heating. Nylon and its forms are thermoplastic (melt on heating) and this property is useful in the production of useful items. The polymer is produced in granular form and then transported to the factory where it is heated and reformed into useful shapes.

A comparison is made between Nylon 6, 10, Nylon 6, 6 and Kevlar explaining that the shorter the monomer chains the stronger the dipole-dipole interaction and hence higher melting point. Dipole-dipole interactions are not strong enough to make the substance rigid but allow the shape to change and then return to shape when the stretching force is reduced (provided the material doesn’t snap).

Polyester (Terylene) is another type of condensation polymer. It is formed from copolymers – one being diacid (carboxyl group at both ends) the other dialcohol (hydroxy group at both ends). On polymerisation, water is produced as a by-product and the reaction is repeated many times forming an ester link between the monomers. The program explains why only weak dispersion forces are formed between the chains and hence the lower melting point.

Other widely used polyester polymers are PET bottles, mylar sails, dacron, video tapes and cassette tapes. Having only dispersion forces between the chains does not allow the material to stretch.

Some condensation polymers are also thermosetting (i.e. char on heating). These polymers are not linear but form a stable covalent network lattice. In formation, as the molecules collide, the atoms regroup into a more stable arrangement. The program gives a clear picture of how this process repeatedly continues to form the lattice. The covalent lattice requires a large amount of energy to break the bonds. Examples of these polymers are urea formaldehyde and melamine.

Investigating Polymers Series CONDENSATION POLYMERS

For Class Discussion

1. We are encouraged to recycle soft drink bottles made of PET. What property of the polymer makes it useful for this?

2. Research the following words

Electro negativity

Dipole functional group

Overall, this program explains the difference between addition and condensation polymers. The variation in properties is explained using molecular models showing the causes of the variations in bonding. It gives the students an understanding of how the process occurs and how there is no clear way to define a plastic. Graphic representation of the molecular models help clarify the processes involved.

Investigating Polymers Series CONDENSATION POLYMERS

Student Worksheet

During and after viewing the program answer the following:

1. A polymer is ______

2. Two ways of linking monomers are by

i) ______

ii) ______

3. Sketch molecular models of

Ethene polyethene

4. Sketch molecular models of

Diamino hexane Apidic Acid

5. Sketch the functional groups

Amine Group Carboxyl Group

6. Show how they link

Investigating Polymers Series CONDENSATION POLYMERS

7. How is the condensation reaction different to the addition reaction?

i) ______

ii) ______

iii) ______

8. Indicate the polarity on H

N C

When the nylon polymer is formed, show how the chains are attracted together.

9. Comparing Kevlar with polystyrene, why does Kevlar have a higher melting point even though the monomers are about the same size?

10. What is a co-polymer?

11. What happens to the molecular particles when a substance melts?

12. How is a thermoplastic useful in industry?

13. Nylon 6, 10. Why are the numbers 6 and 10?

14. Why is Nylon 6.6 better to use as an egg flipper?

Investigating Polymers Series CONDENSATION POLYMERS

15. Why is Kevlar a form of nylon?

16. Sketch the functional groups that make up polyester.

17. Sketch the link after joining.

18. Why does terylene have a lower melting point and less elasticity than many nylons?

19. How does PET get its name and why is it easily recycled?

20. a) Sketch the co-polymers that make urea formaldehyde.

b) Sketch some of the polymer lattice.