Polymers History of Polymers

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PolymersHistory 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.
• The history of plastics is difficult to pin down.
  Man has been using polymers such as shellac,
  horn, gutta, percha, bitumen, lacquer and amber
  for centuries.

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PloymersHistory of polymers

• It is not surprising that 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

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PolymersHistory 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.

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PolymersStructure 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.

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Polymersstructures

• Polymers consist of long chains, which are
  composed of simple structural units (mers) strung
  together.

poly many
mer
mer
mer
mer
mer
mer
mer
mer
mer
Mers strung together to form polymers
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Polymersstructures

• 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. However, if two
  people link together with one hand each and dont
  use the other hand they can only form pairs, such
  molecules cant form mers.

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Polymersstructures
Closed molecule
One-handed

• 1

Two-handed
Linear molecule
Three or more handles
Cross-linked polymers
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Polymersstructures Types of chains

• 1-Linear chains
• Thesse 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.

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Polymersstructures

• 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

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Polymersstructures 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.

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Polymersstructures Thernmoset and Thermplastics

• 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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Polymers Polymerisation Methods of sticking
Mers together

• The process of sticking mers together is called
  polymerisation. The two ways of doing this are
• 1- Additional polymerisation, this is the most
  important of the two because most important
  polymers are made this way and,
• 2- Condensation polymerisation. This method tends
  to yield rigid plastics.

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Polymers Addition Polymerisation

• The basic idea of sticking mers together like
  this is similar to a zip. The mers are added onto
  the end of a growing chain. There are three basic
  parts to the process
• Initiation - Polyethylene C2H4, has a double bond
  between the carbon atoms. One of these bonds is
  stronger, while the other is weak. Each bond
  contains two electrons. The weak bond is attacked
  by a radical.

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Polymers Addition Polymerisation

• This radical grabs an electron and leaves one
  electron behind.
• Propagation -When other ethylene molecules come
  near the ethylene radical they too are attacked
  and a mer is attached. The combined molecule is a
  growing chain radical. The process continues by
  adding other ethylene molecules in a similar
  fashion.

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Polymers Addition Polymerisation

• Termination - Possible stops to the growing
  chains could simply be running out of mers or
  radicals.
• R-C-C -C-C R-C-C-C-C-

Radical
H H
H H H H
H H
H H
H H
H H H H
polyethylene
Ethylene
Addition Polymerisation
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Polymers Condensation Polymerisation

• This process depends on splicing rather than
  zipping. The starting molecules are spliced or
  joined together with small molecules, like water,
  being condensed out of the reaction at the end of
  polymerisation. The remaining structure is a
  comples 3D structure which is rigid and has a
  significant cross-linking feature.

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Polymers Condensation Polymerisation
H C O H
Formaldehyde

• .

OH
Phenol
OH
OH
H C H
H2O
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Polymers Types of Polymers

• Thermoplastics
• These are thermosoftening polymers and make up
  about 85 - 90 of the bulk of polymers. They
  include
• High Density Polyethylene --HDPE
• Low Density Polyethylene --LDPE
• Poly Vinyl Chloride --PVC
• Polystyrene -- PS
• Polypropylene -- PP

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Polymers Types of Polymers

• Thermosetting
• The important ones in this group include
• Phenolics - This is a group of polymers based on
  phenol formaldehyde (PF) the original developed
  by bakeland. It is a cheap, brittle, muddy-brown
  (0r black or blue) polymer.
• Urea-formaldehyde - A white polymer that can be
  easily coloured. Uses include electric plugs,
  sockets, and other fittings.

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Polymers Types of Polymers

• Melamine-formaldehyde. This is harder, more
  scratch resistant and clearer. It can be found in
  melaware and formica table tops
• Polyesters - This is the resin used in fibreglass
  production.
• Epoxies - Tis polymer is used in adhesives.
• Polyurethanes - Are hard to classify as they can
  exist as hard glassy polymer or as a soft
  flexible sponge.

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Polymers Additives for Polymers

• Just as metals are alloyed to improve their
  properties, substances are added to polymers to
  improve theirs. A typical example