Natural And Synthetic Polymers

Polymerisation (addition and condensation) of plastics. Thermosplastic and thermosetting polymers, resins. A polymer is the final product, a macromolecule of high molecular mass. 

It consists of repeating units, and its general molecular formula may be represented as [repeating units]_n where n is a very large whole number.

N.B:   All polymers are macromolecules, but not all macromolecules are polymeric.

NATURAL POLYMERS

These are organic compounds which can be found in living things, e.g. carbohydrates like starch and cellulose, and all proteins, fats and oils are not large enough to be grouped as a giant molecule or polymer.

SYNTHETIC POLYMERS

These are called plastics, e.g. nylon, polythene etc.

EVALUATION

1. State a difference between natural polymers and synthetic polymer with example each.
2. What is another name for synthetic polymer?

POLYMERIZATION

This is the process whereby two or more monomers link/join together to form a compound of

high molecular mass.

TYPES OF POLYMERIZATION

1. Addition polymerization: these occur when two or more of the same monomers join together    to form the polymer without elimination of any small molecules.

CHARACTERISTICS OF MONOMER

1. It must be simple.
2. Unsaturated
3. There should be double bonds between the carbon atom.

e.g.n[CH₂CH₂ ]              ……..CH₂CH₂[CH₂CH₂]_nCH₂CH₂……

2. CONDENSATION POLYMERIZATION:- This is a process whereby two or more smaller molecules (monomers) join together to form a giant molecule (polymer) with the elimination of trace/small molecules such as water, ammonia, and hydrogen chloride.

TYPES OF CONDENSATION POLYMERIZATION

1. COPOLYMER:- This is formed from two condensing monomers of different types.
2. HOMOPOLYMER:- It is formed from monomers of the same type.

CONDITIONS NECESSARY FOR POLYMERIZATION

1. High temperature
2. High pressure
3. Presence of catalyst (initiator) e.g. oxygen, hydrogen peroxide.

EVALUATION

1. State two conditions necessary for polymerization of ethane to from polythene.
2. Mention one difference between additional polymerization and condensation polymensation.

PLASTICS

Plastics are synthetic, which can be heated or pressured to form any shape.

THERMOPLASTIC

Thermoplastics are a type of synthetic material which can be heated and remoulded to any shape e.g. nylon, polythene, polypropene, Perspex, etc.

THERMOSETS

Thermosets, on the other hand, cannot be softened or melted by heat and remoulded once they are formed, e.g. urea-methanal, bakelite.

   Thermoplastics and thermosets

Thermoplastics	Thermosets
Polythene	Bakelite
Polypropene	Urea-methanal
Polystyrene
Nylon
Terylene
Perspex

 RESINS

This is obtained from the rubber tree.  The fluid obtained from the tree can be heated and changed to an elastic solid known as rubber.  The rubber consists of 2-methyl but-1, 3-diene monomers known as isoprene.

CH₃

nCH₂ =      C         CH    =    CH₂

2 – methylbuta-1, 3-diene.

VULCANIZATION

This is the process of heating natural rubber with sulphur to give rubber a greater tensile strength, durability and elasticity over a wide range of temperatures.

SYNTHETIC RUBBER

Examples of synthetic rubbers are poly 2-chlorobuta-1,3-diene, styrenebutadiene rubber (SBR), poly bute -1, 3- diene and poly 2-methyl propene.

EVALUATION

1. What is resin?
2. State two (2) differences between thermoplastic and thermoset.

WEEKEND ASSIGNMENT

1. The following are examples of small molecules formed during polymerisation process.
2. acid   B.  HCl  C.H₂O  D.  NH₃
3. Polymerisation of ethane produces ……………
4. Perspex            B.  isoprene                  C.  polythene          D.  ammonia
5. Bakelite is a good example of …………..
6. natural rubber     B.  thermoset     C.  thermoplastic   D.  additional polymerisation
7. Starch and cellulose are good examples of …………
8. polythene            B.  natural polymer       C.         synthetic polymer    D.  food
9. Joining together of smaller molecules to form a giant molecule is called ………..

process.       A.  hydrogenation   B.  saponification   C.  esterification  D.  polymerization

THEORY

1            (a)      What are the conditions necessary for polymerization.

(b)      List two types of polymerization.

2            (a)      Write an equation for the preparation of polythene from ethane.

(b)      What are the monomer present in the following:

–           polythene

–           polyvinyl/chloride

–           polytetrafluoro ethane

–           polypropene