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					Polymers
History of Polymers



A plastic material is one that is easily shaped and
  takes on a permanent set.

The term polymer refers to a material which has
  been made by some polymerisation process.

Additives and polymers combined yield plastics.

Man has been using polymers such as shellac,
 horn, gutta, percha, bitumen, lacquer and
 amber for centuries.
Ploymers
History of polymers

Research was undertaken to develop and improve
 on nature, thus synthetic polymers were
 developed.

With an increase in understanding in the structure
 of these materials there was rapid development
 in the technology of polymers. Their historical
 development generally follows five stages:
Polymers
History of Polymers


1- from earliest time to 1900: the realisation of a
  new material group,
2- 1900 -1930 The birth of a plastic technology,
3 - 1930 -1950 Plastics as substitute materials
4 - 1950 1970 The “Plastics” age
5 - 1970 - now Engineering Plastics.
Polymers
Structure of polymers
New polymers are being discovered and
 developed all the time. Many are developed for
 particular property combinations which are
 required for specific tasks.

Until 1920 people thought polymers were just thick
 jellies or liquids like bitumen. Nobody really
 understood them fully.

In 1920 Staudinger showed that polymers were
  composed of very large molecules,- thus the
  term polymer was developed.
Polymers
structures
Polymers consist of long chains, which are
  composed of simple structural units (mers)
  joined together.


     mer      mer                       “poly” = many

    mer
             mer                      mer      mer      mer

    mer      mer
           Mers strung together to form polymers
Polymers
structures
There are lots of different types of mers that can
  join together to form polymers.

Mers are simple organic molecules. These are
 special molecules that will link together such as
 double link molecules.

These are like linking arms together to form a
  human chain.
    Polymers
    structures
                                     Closed molecule
        One-handed
1


     Two-handed                 Linear molecule



Three or more
   handles           Cross-linked
                      polymers
Polymers
Types of chains
 1-Linear chains
 These are formed when chains are built up without any
   deviation. They are generally formed when the mers
   used have only two reactive sites.

 2-Branched chains
 Deviation can occur when the chain is being formed and
   chain branching can result.

 3- Cross-linking
 The branches can join up to give cross-links between
    adjacent chains.
Polymers
structures
Level 1      The types of mers

Level 2      Combining mers together

Level 3      The way mers are joined together

Level 4      The degree of order in polymers

Level 5      Polymer mixtures
  Polymers
  Thermoset         and         Thermplastics
The basic structure of polymers is that the mers are
  strung together in chains. Analogies like paper clip
  chains and spaghetti are very useful.

There is a strong covalent bond along the length of the
   chain. The way the chains relate to each other
   determines the type of structure and, hence
   properties.
If the bonds between the chains are primary then a rigid
   3D network is constructed and a Thermoplastic
   polymer will result.
Polymers
Thermoset        and         Thermoplastics

If the bonds between the chains are weak
   secondary bonds, then these will easily be
   disrupted by heat. Such polymers are termed
   Thermoplastics.

The difference is explained by describing how
  butter can be melted in a frying pan and when
  allowed to cool, will harden again. Whereas if an
  egg is broken and fried in the pan until hard, it
  cannot be resoftened.

				
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