POLYMERIZATION

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POLYMERIZATION

  1. 1. Augustine Adu 1 | P a g e KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGY, KUMASI COLLEGE OF SCIENCE DEPARTMENT OF CHEMISTRY PRATICAL CHEMISTRY IV ORGANIC PRACTIAL 2.2.3 NAME: ADU AUGUSTINE
  2. 2. Augustine Adu 2 | P a g e POLYMERIZATION AIMS AND OBJECTIVES: To study formation of polymers. INTRODUCTION Polymers are high molecular weight compounds, many of which have molecular weight exceeding one million. The process of forming high molecular weight molecules from smaller units is called polymerization. The high molecule is called polymer and the smaller unit is called monomer. The monomer may be alike or they may be different. Where two or more monomer are involved in the formation of a polymer, the macromolecule form is called copolymer. Some polymer such as starch, glycogen, cellulose, and protein occur naturally. However many polymers are made including such common substances as polyethylene, polystyrene or Styrofoam, nylon, Dacron, Bakelite, and polyvinyl chloride. Polymers are the basis of all plastics. Some polymers soften on heating ad can be change into different usable shapes; these polymers are known as thermoplastic polymers. Other polymers that are set into infusible solid and do not soften on heating are also known as thermosetting polymers. Polymers are either addition polymers or condensation polymers. An addition polymer is formed by the successive addition of repeating monomer units. A condensation polymer is formed by from monomers with the elimination of water. Classification of polymers: Polymers (synthetic)
  3. 3. Augustine Adu 3 | P a g e 1. Thermoplastics (plastics) - they are linear, some cross-linking and can be melted and reformed on heating a. Amorphous have no ordered structure b. Semi-crystalline. These are composed of microscopic crystallites and domains of crystalline structure. Fibers (nylon, polyester) 2. Elastomers (rubbers) - They are moderately cross-linked, and can be stretched and rapidly recover their original dimension 3. Thermostats (resins) - They are massively cross-linked very rigid; degrade on heating 4. Dendrimers - They are multiply branched and multiple consecutive (regular) branches CHEMICALS AND EQUIPMENT Methanol Ureare Conc. Sulphuric acid Stirrer Boiling tube PROCEDURE
  4. 4. Augustine Adu 4 | P a g e Pour 2cm3 of methanal into and add small amount of urea and shake until it dissolves. Continuously add urea until a saturated solution is obtained. Pour the saturated solution into another boiling tube. Add about one to two drops of concentrated sulphuric acid with care. Stir the mixture without looking into it. The reaction may be violent. Allow the mixture to cool. Record observation during cooling. Weigh the product. RECORDED DATA Weight of empty boiling tube = 38.162g Weight of boiling tube and polymer = 42.701g Weight of polymer = 42.701-38.162 = 4.539g PRECAUTION  Methanal solution (also known as formaldehyde solution, or formalin) should be in good condition. Because the vapour is unpleasant as well as toxic, the supply of this solution for this demonstration should be kept in the fume cupboard, in a stoppered bottle.  The acid used should be sulfuric acid, and NOT hydrochloric acid, because of the possibility of forming the carcinogen, bis-chloromethylether.  Eye protection goggles and hand gloves must be worn for the vapour is harmful to heath. DISCUSSION Urea is dissolved in aqueous methanal in a boiling tube container. Acidification of this solution initiates condensation polymerisation, and a hard, white, thermosetting polymer is formed within a few minutes.
  5. 5. Augustine Adu 5 | P a g e After washing, the properties of this substance can be investigated. If a mould is used, the experiment can be extended to show the formation of plastic articles made in a mould by condensation polymerization. The reaction is a condensation polymerisation in which water is eliminated as the hydrogen atoms from the ends of one amino-group from each of two urea molecules combine with the oxygen atom from a methanal molecule. The remaining –CH2– group from the methanal molecule then forms a bridge between two neighbouring urea molecules, as shown below. This process, repeated many thousands of times, forms long chains of urea and methanal molecules linked together. Sometimes the second hydrogen atom on an amino-group will also react with a methanal molecule, producing a branch in the chain, and chains may even become cross-linked to each other. Eventually a random three-dimensional network of cross-linked chains is formed, giving a rigid structure and thus a hard, inflexible material. ANSWERS TO LABORATORY QUESTIONS. 1. Polymer is a substance that consist of very large molecules called macromolecules that are made up of many repeating subunits. The molecular subunits that are used to synthesize polymers are called monomers. 2. Urea – methanol 3.
  6. 6. Augustine Adu 6 | P a g e 4. Uses of polymers I. They are used as plastic bags, bottles and coating electrical wire. II. They are used in making car tyres. III. Polyesther and nylon are used for making cloths. 5. Monomer Polymer I. Ethylene Polyethylene II. Phenylethene Polystyrene III. Propene Polypropene IV. Chloroethene Polychloroethene or PV V. Tetrafluoroethene Polytetrafluoroethene CONCLUSION The purpose of the experiment was achieved the mass of the polymer formed is 4.539g. REFERENCE Graham Solomons Organic chemistry 10th edition page 487. Francis A. Carey organic chemistry page 445-447. KNUST chemistry Laboratory manual.

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