Polymers

Polymers

1. Polymerisation is the process through which monomers (if the number of monomer increases so does the mass) are linked to each other by covalent bonds to create polymers.

2. Polymers are very large molecules that have a high molecular mass between 10(3)-10(7)U.

3. Aspects in which polymers are classified

   • Classification based on the source
     • Natural Polymers
       • Found in nature; these include, proteins, cellulose, starch, some resins and rubber.
     • Semi-Synthetic
       • Come from cellulose (cellulose acetate and cellulose nitrate could be the main examples).
     • Synthetic Polymers
       • All of the polymers made by humans such as plastic, synthetic fibres and synthetic rubbers.
   • Classification based on structure
     • Linear Polymers
       • Long straight chains.
     • Branched Chain Polymers
       • Linear polymers that have some branches. Low density polythene is an example of these.
     • Cross linked or Network polymers
       • Formed by bi or tri-functional monomers that contain strong covalent bonds between a number of linear polymers.
   • Classification based on mode of polymerisation
     • Addition Polymers
       • Formed by the repeated addition of monomers possessing double or triple bonds.
     • Condensation Polymers
       • Formed by the repeated condensation of two different bi-functional or tri-functional monomeric units. This reaction usually releases water or any substances that the monomer might contain.
   • Classification based on molecular forces
     • Elastomers
       • Solids with elastic properties; they're held together by the weakest intermolecular forces (the ones to blame for the elasticity of the material). ‘Crosslinks’ are found between the chains, and they're the ones responsible for the retractable properties of these rubbers.
     • Fibres
       • Links of polymers that form solids that posses high tensile strength and high modulus. These strong forces lead to the close packing of chains.
     • Thermoplastic polymers
       • Long chains with some branches, that soften with the presence of heat, and harden upon the presence of cold. The intermolecular forces between these is in between elastomers and fibres.
     • Thermosetting polymers
       • Heavily branched molecules which undergo and extensive cross linking when heated, becoming infusible.
   • Classification based on growth polymerisation
     • Addition and condensation polymers are referred to as chain or step growth polymers, depending on the type of polymerisation they undergo when formed.

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