1. Engineering Materials Polymeric materials
Polymer == many parts
Polymeric material:- is a material that contains many chemically bonded parts or units that themselves are bonded together to form a solid.
In this subject we shall study some aspects of the; 1- Structure 2- Properties 3- Processing, 4- applications, of two industrially important polymeric materials
Polymeric materials
1. Plastics
Thermoplastics
Thermosetting plastics(Thermosets)
2. Elastomers (rubbers)
Elastomers (rubbers)
Can be elastically deformed when a force is applied to them and can return to their original shapes (or almost) when the force is released.

2. Engineering Materials Polymeric materials
Polymer == many parts
Thermoplastics
A plastic martial that requires heat to make it formable, and after cooling, remains its shape. Thermoplastic can be repeatedly softened when heated and harden when cooled. Typical thermoplastics are polyethylene, vinyls, acrylics, cellulosics, and nylons.
thermoplastic pens
thermoplastics objects
thermoplastic resin.

3. Engineering Materials Polymeric materials
Polymer == many parts
Thermosetting plastics
Usually formed into a permanent shape by heat and pressure during which time a chemical reaction takes place that bonds the atoms together to form a rigid solid.
Some thermosetting reactions take place at room temperature without the use of heat and pressure.
Thermosetting plastic cannot be remelted after they are set or cured and upon heating to a high temperature, they degrade or decompose. CAN NOT BE RECYCLED .
Typical thermosetting plastics are phenolics, unsaturated polyesters and epoxies.
The linear chains are crosslinked - strongly chemically bonded. This prevents a thermoplastic object from being melted and reformed

4. Engineering Materials Polymeric materials
Polymer == many parts
Polymerization reactions
Polymerization reactions:- a chemical reaction in which many small molecules are covalently bonded together to form very long molecular chains.
Monomers:- a simple molecular compound that can be covalently bonded together to form long molecular chains (polymers). For example ethylene.
Polymer:- is the long chain molecule formed from the monomer units, example polyethylene.

5. Engineering Materials Polymeric materials
Polymer == many parts
Polymerization reactions
Covalent bonding structure of an ethylene molecule and activated ethylene molecule
Unstaturated molecule: A carbon containing molecule that has one or more Carbon-carbon
double bonds, example ethylene molecule C2H4.
C=C H
single
covalent
bond
double
When the ethylene molecule is activated so that the double bond between the two carbon atoms is (opened up), the double covalent bond is replaced by a single covalent bond.
C C H
Half covalent
Bond or free electron
single
covalent
bond

6. Engineering Materials Polymeric materials
Polymer == many parts
Polymerization reactions
General reaction for the polymerization of poly and the degree of polymerization:
General reaction for the chain polymerization of ethylene monomer into ployethylene may be written as; H
Mer
Polyethylene (polymer)
Ethylene (monomer)
Mer: a repeating unit in a chain polymer molecule.
Degree of polymerization(DP) : is equal to the number of subunits or mers in the
polymer molecular chain. Its equal to the molecular mass of a polymer chain divided
by the molecular mass of its mer.
The average DP for the polyethylene ranges from about 3500 to 25,000,
corresponding to average molecular masses ranging from about 100,000
to 700,000 g/mol.

7. Engineering Materials Polymeric materials
Polymer == many parts
Polymerization reactions
Example. If a particular type of polyethylene has a molecular mass of 150,000 g/mol, what is its degree of polymerization (DP)?
Solution/ the repeating unit or mer for polyethylene is –[CH2–CH2]–. This mer has a mass of 4atoms x 1g =4g for the hydrogen atoms plus a mass of 2 atoms x 12g=24 g for the carbon atoms, making a total of 28 g for each polyethylene mer. H
Mer
Polyethylene (polymer)
Ethylene (monomer)

8. Engineering Materials Polymeric materials
Polymer == many parts
Polymerization reactions
Problem1. A high molecular weight polyethylene has an average molecular weight of 410,000 g/mol. What is its average degree of polymerization?
Problem2. If a type of polyethylene has an average degree of polymerization of 10,000, what is its average molecular weight?

9. Engineering Materials Polymeric materials
Polymer == many parts
Polymerization reactions
Chain polymerization steps:- the polymerization reaction can be divided into the following steps;
1- initiation 2- propagation and 3- termination.
1. Initiation:-
To start the polymerization reaction we need a catalyst called organic peroxide that act as free radical formers.
Free Radical is an atom/molecule that has a free electron that can covalently bond to a free electron of another atom/molecule
Free electrons

10. Engineering Materials Polymeric materials
Polymerization reactions
Chain polymerization steps:
1. Initiation:-
One of the free radicals created by the decomposition of the organic peroxide can react with an ethylene molecule to form new longer chain free radical. H
Initiator catalyst for
the polymerization of
ethylene

11. Engineering Materials Polymeric materials
Polymerization reactions
Chain polymerization steps:
2. Propagation:-
is the process of extending the polymer chain by the successive addition of monomer units. H
Initiator catalyst for
the polymerization of
ethylene

12. Engineering Materials Polymeric materials
Polymerization reactions
Chain polymerization steps:
3. Termination:-
can occur by the addition of a terminator free radical or when two chains combine. Another possibility is that trace amount of impurities may terminate the polymer chain. H
Initiator catalyst for
the polymerization of
ethylene

13. Molecular weigh range ( g/mol)
Engineering Materials
Polymeric materials
Polymerization reactions
Average molecular weight for thermoplastics:
Example:- calculate the average molecular weight for a thermoplastic material that has the mean molecular weight fractions for the molecular weight ranges listed in the following table:
Molecular weigh range ( g/mol)
weight fraction
5000 – 10,000
0.11
10, ,000
0.17
15, ,000
0.26
20, ,000
0.22
25,000-30,000
0.14
30,000 – 35,000
0.10

14. Engineering Materials
Polymeric materials
Polymerization reactions
Functionality of a monomer:
The number of active bonds a monomer has is called functionality of a monomer.
A monomer that uses two active bonds for the polymerization of long chain is called
bifunctionality. Ethylene C2H4 is an example of a bifunctionality monomer.
A monomer that uses three active bonds to form a network polymeric material is called trifunctionality. Phenol (C6H5OH) is an example of a trifunctionality monomer and is used in the polymerization of phenol and formaldehyde.

15. Engineering Materials
Polymeric materials
Polymerization reactions
Homopolymers and Copolymers
Homopolymers:- are polymeric materials that consist of polymer chain made up of single repeating units. If A is a repeating units, a homopolymer chain will have a sequence of AAAAAA …. in the polymer molecular chain.
Copolymers:- are polymeric materials that consist of polymer chain made up of two or more chemically different repeating units that can be in different sequences.
Random copolymers:- Different monomers are randomly arranged within the polymer chains. If A and B are different monomers, the arrangement might be,
AABABBBBAABBBBBAAABAAA…..

16. Engineering Materials
Polymeric materials
Polymerization reactions
Homopolymers and Copolymers
Alternating copolymers:- Different monomers show a definite ordered alternation as
ABABABABABABABABA…..
Block copolymer:- Different monomers arranged in relatively long blocks of each monomer as, AAAAA - BBBBB -…..
Graft copolymer:- Appendages of one type of monomer are grafted to the long chain of another as, AAAAAAAAAAAAAAAAAAAAAA
B B

17. Engineering Materials
Polymeric materials
Polymerization reactions
Homopolymers and Copolymers
Example 3:- A copolymer consists of 15 wt% polyvinyl acetate (PVA) and 85 wt% polyvinyl chloride (PVC). Determine the mole fraction of each component.
Molecular weight of the PVA mer and PVC mer can be calculated from;
Structural formulas for the mers of polyvinyl chlorid (PVC)
Structural formulas for the mers of Polyvinyl acetate (PVA)
Example 4:- Determine the mole fractions of vinyl chloride and vinyl acetate in a copolymer having a molecular weight of 10,520 g/mol and a degree of polymerization of 160.
Example 5:- If a vinyl chloride - vinyl acetate copolymer has a ratio of 10:1 vinyl chloride to vinyl acetate mers and a molecular weight of 16,000 g/mol, what is its degree of polymerization ?

18. Engineering Materials
Polymeric materials
Polymerization reactions
Industrial polymerization methods
Bulk polymerization:- Monomer plus activator are mixed in a reactor that is heated and cooled as required.

19. Engineering Materials
Polymeric materials
Polymerization reactions
Industrial polymerization methods
Solution polymerization:- The monomer is dissolved in a non reactive solvent that contains a catalyst. The heat released by the reaction is absorbed by the solvent.

20. Engineering Materials
Polymeric materials
Polymerization reactions
Industrial polymerization methods
Suspension polymerization:- The monomer is mixed with a catalyst and then dispersed as a suspension in water. The heat released by the reaction is absorbed by the water. After polymerization, the polymerized product is separated and dried. This process is commonly used to produce polyvinyl chloride (PVC), polystyrene, polyacrylonitrile.

21. Engineering Materials
Polymeric materials
Polymerization reactions
Industrial polymerization methods
Emulsion polymerization:- Is similar to the suspension process since it is carried out in water. However, an emulsifier is added to disperse the monomer into very small particles.

22. Engineering Materials
Polymeric materials
Polymerization reactions
Industrial polymerization methods
Solution polymerization:- The monomer is dissolved in a non reactive solvent that contains a catalyst. The heat released by the reaction is absorbed by the solvent.
Solution polymerization of ethylene, using Ziegler-Natta catalysts