The Structure and Properties of Polymers

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The Structure and Properties of Polymers
monomer
polymer
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What is a polymer?

• A long molecule made up from lots of small
  molecules called monomers.

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All the same monomer

• Monomers all same type (A)
• A A A A ?
• -A-A-A-A-
• eg poly(ethene) polychloroethene PVC

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Different monomers to form Copolymers

• Monomers of two different types A B
• A B A B
• ? -A-B-A-B-
• eg polyamides
• polyesters

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Copolymerisation

• when more than one monomer is used.
• An irregular chain structure will result eg
  propene/ethene/propene/propene/ethene
• Why might polymers designers want to design a
  polymer in this way?
• (Hint) Intermolecular bonds!

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The Structure of Polymers (plastics)

• Polymers are created by the chemical bonding of
  many identical units . These polymers are
  specifically made of small units bonded into long
  chains. Carbon makes up the backbone of the
  molecule and hydrogen atoms are bonded along the
  carbon backbone.

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The Structure of Polymers (plastics)

• Polymers that contain primarily carbon and
  hydrogen are classified as organic polymers.
  Polypropylene and polystyrene are examples of
  these.Even though the basic makeup of many
  polymers is carbon and hydrogen, other elements
  can also be involved. Oxygen, chlorine, fluorine,
  nitrogen, silicon, phosphorous and sulfur are
  other elements that are found in the molecular
  makeup of polymers.
• Polyvinyl chloride (PVC) contains chlorine.
• Nylon contains nitrogen. Teflon contains
  fluorine.
• Polyester and polycarbonates contain oxygen.

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The Structure of Polymers (plastics)

• There are also some polymers that, instead of
  having a carbon backbone, have a silicon or
  phosphorous backbone and these are considered
  inorganic polymers.

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Natural Polymers

• Wool, cotton, linen, hair, skin, nails, rubber,
  and flesh are all naturally occurring polymers
• Most naturally polymers are made of protein or
  cellulose

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Synthetic Polymers

• Commonly referred to as plastics pliable, able
  to be moulded

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• The bonding process.
• When thermoplastic polymers are heated they
  become flexible. There are no cross-links and the
  molecules can slide over each other.
• Thermosetting polymers do not soften when heated
  because molecules are crosslinked together and
  remain rigid.

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Thermoplastics (80)

• No cross links between chains.
• Weak attractive forces between chains broken by
  warming.
• Change shape - can be remoulded.
• Weak forces reform in new shape when cold.

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Thermoplastics

• Those which soften on heating and then harden
  again on coolingThese are called thermoplastic
  polymers because they keep their plastic
  properties
• These polymer molecules consist of long chains
  which have only weak bonds between the chains
• The bonds between the chains are so weak that
  they can be broken when the plastic is heated
• The chains can then move around to form a
  different shape
• The weak bonds reform when it is cooled and the
• thermoplastic material keeps its new shape

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Thermosets

• Extensive cross-linking formed by covalent bonds.
• Bonds prevent chains moving relative to each
  other.
• What will the properties of this type of plastic
  be like?

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Thermosetting

• Those which never soften once they have been
  moulded These are called thermosetting polymers
  because once set into a shape, that shape cannot
  be altered
• These polymer molecules consist of long chains
  which have many strong chemical bonds between the
  chains
• The bonds between the chains are so strong that
  they cannot be broken when the plastic is heated
• This means that the thermosetting material always
  keeps its shape

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Addition Polymerisation

• When ethene is subjected to high pressure it
  changes from a gas to a liquid
• Liquid ethene (still under high pressure) is
  heated in the presence of a catalyst (O2), an
  addition reaction takes place.
• For addition polymerisation to occur, the monomer
  must have a double C bond.
• This bond breaks to allow the long chains to
  form.
• Modifying ethene, substituting different
  functional groups for hydrogen atoms produces
  other monomers that can be polymerised to make
  polymers with different properties.

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Addition polymerisation

• Monomers contain CC bonds
• Double bond opens to (link) bond to next monomer
  molecule
• Chain forms when same basic unit is repeated over
  and over.
• Modern polymers also developed based on alkynes
  R-C C - R

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Addition Polymerisation

• A carbon carbon double bond is needed in the
  monomer
• A monomer is the small molecule that makes up the
  polymer

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Addition Polymerisation

• The polymer is the only product
• Involves the opening out of a double bond
• The conditions of the reaction can alter the
  properties of the polymer
• Reaction proceeds by a free radical mechanism
• Oxygen often used as the initiator

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Addition polymerisation
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Addition polymerisation

• Conditions are high pressure and an oxygen
  initiator (to provide the initial free radical).
• Monomer phenylethene
• Polymer poly(phenylethene)

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Prediction the repeating unit

• This is easy, basically open out the double bond.
  

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Review

• Work through the sample problem page 200

• Complete the revision questions page 200 (1 - 2)

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Linear polymers with side branches

• Linear polymers are those in which the main
  backbone is unbranched.
• The way in which side branches are arranged on
  linear polymers (polypropylene) can affect the
  properties of the polymer.

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Linear polymers with side branches

• Isotactic
• Same side of the linear polymer
• Greater effect of dispersion forces therefore
  high density, rigid and tough and a high
  softening temp.

• Atactic
• Irregular points on both sides of the linear
  polymer
• Chains of molecules cannot get close together,
  therefore low density.
• Soft, waxy little use

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Poly(propene)

• This varying degree of randomness will affect the
  strength and melting point of the polymer.
• The less random, the stronger the polymer and the
  higher the melting point
• This is because in a more ordered polymer they
  chains can get closer together and hence the van
  der Waals forces will be greater.

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Linear polymers with cross links

• Cross links are covalent bonds that can form
  between polymer chains.
• If the number of crosslinks is small an elastomer
  (vulcanised rubber) will result.
• If the number of crosslinks is large a hard
  inflexible thermosetting polymer will be
  produced.

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Linear polymers with cross links

• To make a thermosetting polymer, the linear
  chains are produced first
• The cross linking is brought about either by heat
  or by adding a chemical to react between the
  lateral functional groups linking the chains
  together.
• Araldite is a good example of a two part glue
  the 2nd method of producing a thermosetting
  polymer.

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Condensation Polymers

• Condensation polymerisation uses monomers that
  have two functional groups per molecule.
• These are said to be difunctional.
• Polymerisation occurs when these monomers react
  head-to-tail to form a new bond that will
  eventually join the monomers together
• A small molecule (often water) is eliminated
• condensation polymerisation simulation

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Condensation Polymers

• Suitable functional groups
• -NH2 amine -OH alcohol
• O O
• -C carboxyl -C acid
  chloride
• OH Cl

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Condensation Polymers

• Involves 2 monomers that have different
  functional groups.
• They also involve the elimination of water or
  another small molecule.
• Hence the term condensation polymer.
• Monomer A Monomer B ? Polymer small molecule
  (normally water).
• Common condensation polymers include polyesters
  (the ester linkage) and polyamides (the amide
  linkage as in proteins).
• May be natural (protein, starch, cotton, wool,
  silk) or synthetic (viscose, nylon, polyester)

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Polyesters

• The OCR example here is terylene, a polymer of
  benzene-1,4-dicarboxylic acid and
  ethane-1,2-diol.
• The ester linkage is formed between the monomers

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Polyesters

• The structures of other polyesters

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Polyamides

• These involve the linkage of two monomers through
  the amide linkage as in proteins (e.g. silk)

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Nylon 6,6 a polyamide
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Kevlar a polyamide
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Uses of polyamides

• The main use of polyesters and polyamides is as
  fibres in clothing.
• Most clothing now has a degree of manufactured
  fibres woven into the natural material (such as
  cotton).
• This gives the material more desirable
  characteristics, such as stretchiness, and better
  washability.
• Dont forget that proteins are also polyamides,
  you must know how the linkage works with natural
  polymers such as proteins.

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Review

• Complete the revision questions page 202 (3 5)

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Commonly used polymers

• What would life be without polymers?

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Addition Polymers

• PVC, Teflon, Polystyrene check table 9.1 page
  198

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Addition Polymers

• Ethene can be polymerised to produce both low and
  high density polyethene (commonly known as
  polyethylene)
• LDPE produced with high temp and high pressure
  long side chains low density (plastic bags)
• Soft, flexible and translucent with a waxy
  surface that repels water.
• HDPE produced with lower temp and pressure very
  few short branches dispersion forces more
  effective high density (plastic bottles)
• Rigid, stronger and more opaque than LDPE
• Slightly flexible, waxy surface that repels water

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Addition Polymers

• Rubber is an addition polymer that occurs
  naturally
• The monomer in natural rubber is isoprene. It
  polymerises to form long chains.
• Molecular formula (C5H8)n
• Rubber still contains double bonds which can be
  attacked by oxygen and can perish (unlike
  polythene)

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Addition Polymers

• Rubber
• not elastic long chains straighten out when
  stretched and remain this way
• Susceptible to temperature changes brittle when
  cold and sticky when hot.
• Vulcanisation improved durability and elasticity
  of rubber.
• The linear chains are cross linked using heat and
  sulfur

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Condensation Polymers

• Nylon
• Can be extruded when molten to form fibres or
  sheets of strong, durable and elastic material
• Its invention had a great impact on the textile
  and clothing industries.

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Condensation Polymers

• Nylon 6 6
• Nylon is a linear chain containing up to 100
  repeated units.
• The name nylon 6 6 refers to the existence of 6
  carbon atoms on each of the units

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Condensation Polymers

• PET plastic Polyethene terephthalate.
• Soft drink bottles
• An example of a polyester
• Note the removal of H2O (condensation polymer)

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Polymer Selection

• Due to their versatility, polymers can be
  produced for almost any imagined purpose.
• A huge range of polymers exist today and are used
  for many different applications.
• Their versatility has made them one of them one
  of the most useful classes of substances that we
  rely on in todays society.
• This versatility can be attributed to the many
  different ways that they can be modified

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Recycling

• Most plastics are produced from crude oil, coal
  or gas.
• Many of them are not biodegradable and have
  become a visible part of our environmental litter.

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Review

• Polymers on line multiple choice
• Polymers quiz on line
• Complete the multiple choice questions pages 212,
  213 (1 12)
• Complete the review questions 3, 6, 7, 9, 11, 13,
  16, 19, 21