Polymers

Polymers

1. Polymers

   • Poly = Many
   • Mers = Unit
   • Monomers
     • Many monomers form a polymer
     • Linked by covalent bonds
       • Polymerization
   • Polymer Classification
     • Natural
       • From plants and animals
     • Synthetic
       • Are produced in different types of chemical reactions
     • Semi synthetic
       • Are made from a mix of both synthetic and natural polymers
     • Based on structure
       • Linear polymers
         • Highly dense
       • Branched chain polymers
         • Low-density polythene
       • Cross linked or Network polymers
         • Bi or tri functional polymers, strong covalent bonds
     • Based on Polymerization Mode
       • Addition Polymers
         • formed by the repeated addition of monomer molecules possessing double or triple bonds
         • Homopolymers
           • Polymerization of a single monomeric species
         • Copolymers
           • Polymerization from two different monomers
       • Condensation
         • Is formed by repeated condensation reactions between two different bi-functional or tri-functional monomeric units. Elimination of small molecules.
     • Based on Molecular Forces
       • Elastomers
         • The polymer chains are held together by the weakest intermolecular forces
       • Fibers
         • This has strong intermolecular forces and close packing of chains
       • Thermoplastic Polymers
         • Soft in heat, hard in cold. They are an intermediate between elastomers and fibers.
       • Thermosetting Polymers

2. Addition Polymerisation or Chain Growth Polymerisation

   • In this type of polymerisation, the molecules of the same monomer or different monomers add together on a large scale to form polymer. The monomers used are unsaturated compounds, e.g., alkenes, alkadienes
   • Free radical mechanism
     • A variety of alkenes or dienes and their derivatives are polymerised in the presence of a free radical generating initiator (catalyst)
   • Preparation of some important addition polymers
     • Polythene
       • Low density polythene made by polymerisation of ethene or high density polythene that is made with polymerisation of ethene but is is solve in a solvent hydrocarbon
     • Polytetrafluroethene (teflon)
       • Is made by heating tetrafluoroethene with a catalyst
     • Polyacrylonitrile
       •  The addition polymerisation of acrylonitrile

3. Condensation Polymerisation (step growth polymerisation)

   • Condensation reaction repeated times. Two bi-functional monomers
   • Loss of water, alcohol, or more
   • The process results in high molecular mass condensation polymers
   • Reactions for condensation polymerisation
     • Polyamides
     • Polyesters
     • Phenol
     • Melamine

4. Copolymerisation

   • At least 2 monomeric species polymerise to form copolymers
   • Can be made by chain growth and step growth polymerisation
   • Natural Rubbers
     • Natural Polymer. Comes from rubber latex.
   • Synthetic Rubbers
     • Neoprene
       • Polymerisation of chloroprene
     • Buna - N
       • Comes from copolymerisation.

5. Molecular mass

   • Polymer properties=Molecular mass

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