Condensation polymers

1
Condensation polymers

• C.8.1 Distinguish between addition and
  condensation polymers in terms of their
  structures.
• C.8.2 Describe how condensation polymers are
  formed from their monomers.
• C.8.3 Describe and explain how the properties of
  polymers depend on their structural features.
• C.8.4 Describe ways of modifying the properties
  of polymers.
• C.8.5 Discuss the advantages and disadvantages of
  polymer use.

2
Distinguish between addition polymer and
condensation polymer

• Addition polymer
• formed by an addition reaction, where many
  monomers bond together via rearrangement of bonds
  without the loss of any atom or molecule.
• Usually made from alkenes

• Condensation polymer
• formed by a condensation reaction where a
  molecule, usually water, is lost during the
  formation
• Made from monomers that contain at least two
  reactive functional groups( or same functional
  group at least twice)

3
Formation of polyester

• Polyethen terephthalate (PET)
• When benzene-1,4-dicarboxylic acid and ethane-1,2
  diol reacts

4
Phenol-methanal plastic

• The reaction is a condensation polymerisation in
  which water is eliminated as a hydrogen atom from
  the benzene ring of each of two neighbouring
  phenol molecules combines with the oxygen atom
  from a methanal molecule ( When acid or alkali is
  added to the mixture of phenol and methanal)
• The remaining CH2 group from the methanal
  molecule then forms a bridge between two
  neighbouring phenol molecules. This process,
  repeated many thousands of times, forms chains of
  phenol and methanal molecules linked in this way.

5
Mechanism

• When acid or alkali is added to the mixture of
  phenol and methanol.
• Methanal is substituted in the 2- or 4- position
  in the phenol
• It then undergoes a condensation reaction with
  another phenol molecule.

6
Long Chain

• Long chain of phenol-methanal plastics (covalent
  cross linking three dimensional structure) is
  built up when further polymerization takes place

7
Formation of Polyurethane

• When polyhydric alcohols (e.g. diols or triols)
  reacts with compounds containing more than one
  isocyanate functional group, -NCO will produce
  polyurethanes.

8
Polyurethane

• Polyurethanes are somehow considered as addition
  polymers since there is no small molecules formed
  during the reaction. However there is no urethane
  monomers that add together to form polyurethanes.
• Polyurethanes are made in situ and moulded into
  shape wanted.
• (In the reaction mixture." There are numerous
  unstable molecules which must be synthesized in
  situ (i.e. in the reaction mixture but cannot be
  isolated on their own )

9
Properties of polymers

• Properties of condensation polymers depend on
  their structures.
• The benzene ring bonds in more than one position
  of phenol-methanal plastics forms 3-D
  cross-linked structure

10
Properties

• The structure gives high strength. Therefore the
  compound is
• High melting point ( decompose before melting)
• Unreactive
• High electrical resistance
• It can be use as an ingredient in worktops and
  printed-circuit-board insulation
• Before it was use as the casing for radios

11
Kevlar

• Kevlar is a polyamide
• It forms when 1,2-diaminobenzene
  (paraphenylenediamine) condenses with
  benzene-1,4-dicarbonyl chloride(terephthaloyl
  dichloride)

12
Long chain

• Further polymerization forms a strong
  three-dimensional structure because of the
  hydrogen bonding between the long rigid chain
• Kevlar is used to produce lightweight
  bullet-proof vest, composites for motor-cycle
  helmets and amour.

13
Modification of polymers

• Apart from adding plasticizers (covered in
  addition polymer) there are 3 more ways to modify
  polymers
• Blowing air into polyurethane to make
  polyurethane foams ( cushions and thermal
  insulator)
• Blending fibres of polyesters (PET) with other
  manufactured or natural fibres to make clothes
  become dye-fast and comfortable than pure
  polyesters.

14
Modifying polymer

• Another way is adding chemicals ( this process is
  called doping polymer) such as
• Iodine which removes electrons
• or
• Alkali metals which adds electrons
• When ethyen is polymerized, the cis-form of
  polyethene is a electrical conductor due to the
  deloclization of the pi electrons.
• The conductivity is increaseddramatically after
  doping I2

15
Advantages

• Use to produce lightweight bullet-proof vest,
  composites for motor-cycle helmets and amour.
  (PET)
• Devices such as billiard balls, dominoes,
  Mahjongg tiles and other gaming tilesets, and
  movers/pieces for games like chess, checkers, and
  backgammon, are constructed of Bakelite(phenol-met
  hanal plastics) for the look, durability, fine
  polish, weight, and sound of the resulting pieces
• Polyurethane products have many uses. Over three
  quarters of the global consumption of
  polyurethane products is in the form of foams,
  with flexible and rigid types being roughly equal
  in market size. In both cases, the foam is
  usually behind other materials flexible foams
  are behind upholstery fabrics in commercial and
  domestic furniture rigid foams are inside the
  metal and plastic walls of most refrigerators and
  freezers, or behind paper, metals and other
  surface materials in the case of thermal
  insulation panels in the construction sector.

16
Disadvantages

• The disadvantages of condensation polymer are
  similar to addition polymer
• Low-reactivity ? Not easy to dispose off.
• Generally not biodegradable
• Produce hydrogen cyanide gas when polyurethanes
  are burned.