Polymers

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Polymers

  1. 1. FINAL ASSIGNMENT CHAPTER 16 : POLYMERIZATION
  2. 2. MONOMERS & POLYMERS • Monomers are small molecules used to synthesise polymers. • A polymer is a large molecule made up of many smaller molecules (monomers). • The chemical reaction in which the monomers are joined together by covalent bonds is called polymerization.
  3. 3. CLASSIFICATION OF POLYMERS • Homopolymers – synthesised from a single type of monomer. Example : polyethylene and polypropylene. These may be represented as : -[A-A-A-A-A-A]• Copolymers – formed from two or more different types of monomers are called copolymers. These may be represented as : -[A-B-A-B-A-B]-
  4. 4. Several classes of copolymer are possible • Statistical copolymer (Random) ABAABABBBAABAABB two or more different repeating unit are distributed randomly • Alternating copolymer ABABABABABABABAB are made of alternating sequences of the different monomers • Block copolymer AAAAAAAAABBBBBBBBB long sequences of a monomer are followed by long sequences of another monomer • Graft copolymer AAAAAAAAAAAAAAAAAA B B B B B B Consist of a chain made from one type of monomers with branches of another type
  5. 5. Classification by Chain structure (molecular architecture) • Linear chains : a polymer consisting of a single continuous chain of repeat units • Branched chains :a polymer that includes side chains of repeat units connecting onto the main chain of repeat units • Hyper branched polymer consist of a constitutional repeating unit including a branching groups • Cross linked polymer :a polymer that includes interconnections between chains • Network polymer :a cross linked polymer that includes numerous interconnections between chains Linear Branched Cross-linked Direction of increasing strength Network
  6. 6. NOMENCLATURE / NAMING Generic source-based nomenclature for polymers (IUPAC Recommendations 2001) A generic source-based name comprises two parts: 1) polymer class (generic) name followed by a colon 2) the actual or hypothetical monomer name(s), always parenthesized in the case of a copolymer
  7. 7. Homopolymers RULE 1 • The source-based name of a homopolymer is made by combining the prefix “poly” with the name of the monomer.
  8. 8. General Rules RULE 2 • A generic source-based name of a polymer has two components and always parenthesized in the case of a polymer I. A polymer class (generic) name (polyG) followed by a colon II. The actual of hypothetical monomer name(s)
  9. 9. RULE 3 • When more than one type of functional group or heterocyclic system is present in the polymer structure, names should be alphabetized, example, poly(GG’):(A-alt-B)
  10. 10. RULE 4 • Polymer class names relevant only to the main chain are specified in the name, names of side-chain functional groups may also be included after a hyphen if they are formed during the polymerization reaction.
  11. 11. RULE 5 • In the case of carbon-chain polymers such as vinyl polymers or diene polymers, the generic name is to be used only when different polymer structures may arise from a given monomeric system.
  12. 12. CHARACTERISTICS OF POLYMERS • • • • • • • • • • • Low Density. Low coefficient of friction. Good corrosion resistance. Good mould ability. Excellent surface finish can be obtained. Can be produced with close dimensional tolerances. Economical. Poor tensile strength. Low mechanical properties. Poor temperature resistance. Can be produced transparent or in different colours.
  13. 13. PHYSICAL PROPERTIES The physical properties of a polymer, such as its strength and flexibility depend on: • Chain length - in general, the longer the chains the stronger the polymer; • Side groups - polar side groups give stronger attraction between polymer chains, making the polymer stronger; • Branching - straight, un branched chains can pack together more closely than highly branched chains, giving polymers that are more crystalline and therefore stronger; • Cross-linking - if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.
  14. 14. STRENGTH OF POLYMERS In general, the longer the polymer chain, the stronger the polymer. There are two reasons for this: • longer chains are more tangled • there are more intermolecular forces between the chains because there are more points of contact. These forces, however, are quite weak for polyethene. • Areas in a polymer where the chains are closely packed in a regular way are said to be crystalline. The percentage of crystallinity in a polymer is very important in determining its properties. The more crystalline the polymer, the stronger and less flexible it becomes.
  15. 15. • When a polymer is stretched (cold-drawn), a neck forms. In the neck the polymer chains line up producing a more crystalline region. Cold-drawing leads to an increase in strength. • The first polyethene which was made contained many chains which were branched. This resulted in a relatively disorganised structure of low strength and density. This was called low density polyethene (ldpe). • In the crystalline form, the methyl groups all have the same orientation along the chain. This is called the isotactic form. In the amorphous form, the methyl groups are randomly orientated. This is called the atactic form. • Polymers with a regular structure are said to be stereoregular.
  16. 16. POLYMERIZATION REACTIONS
  17. 17. • Both classes of reaction can lead to the formation of either linear polymers or polymer networks. Whether the linear chains or polymer networks are obtained only depends on the number of reactive entities per monomer.
  18. 18. Molar Mass Distribution
  19. 19. STEP-GROWTH POLYMERIZATION • In step-growth polymerization, a linear chain results from the step-wise condensation or addition of reactive groups of bifunctional monomers.
  20. 20. Condensation Polymerization • Condensation : process in which two monomers react to form a larger molecule and eliminate a smaller molecule (usually water, ammonia, methanol or hydrogen chloride). • Example : Kevlar, nylon, and Terylene.
  21. 21. • Step-Growth polymerization occurs by consecutive reactions in which the degree of polymerization and average molecular weight of the polymer increase as the reaction proceeds. Usually (although not always), the reactions involve the elimination of a small molecule (e.g., water). Condensation polymerization may be represented by the following reactions: Monomer + Monomer Dimer + H2O Monomer + Dimer Trimer + H2O Monomer + Trimer Tetramer + H2O Dimer + Dimer Tetramer + H2O Dimer + Trimer Pentamer + H2O Trimer + Trimer Hexamer + H2O • Generally, the reactions are reversible, thus the eliminated water must be removed if a high molecular weight polymer is to be formed. • Based on the assumption that the polymerization kinetics are independent of molecular size, the condensation reactions may all be simplified to: ~~~~COOH + HO~~~~ ~~~~COO~~~~ + H2O
  22. 22. • When a monocarboxylic acid reacts with an amine, amide is formed. • When a carboxylic acid with two –COOH groups reacts with an amine with two –NH2 groups, a polyamide is formed.
  23. 23. • When a monocarboxylic acid reacts with an alcohol, and ester is formed. • When a carboxylic acid with two –COOH groups reacts with an alcohol with two –OH groups, a polyester is formed.
  24. 24. Addition Polymerization • Addition : monomers with double bonds are joined together by covalent bonds to form a large molecule (polymer) without loss of a small molecule. • Monomers for making addition polymers may be alkenes (ethene and propene) or alkene derivatives (choloroethene, CH2 = CHCl) • In the formation of addition polymers, the carboncarbon double bond in each monomer is broken open and replaced by a carbon-carbon single bond.
  25. 25. • Chain polymerization proceeds by the succession of three steps : – Initiation : The first active center (radical, anion or cation) is formed and the growth of the chain is initiated. – Propagation : Growth of the polymer chain occurs by the successive addition of monomers to the active center at the end of the chain. – Termination : Growth is terminated by either neutralization or transfer of the active center.
  26. 26. • Initiation • Propagation • Termination
  27. 27. Vinyl monomers for addition polymerizations The only exceptions to the unreactivity of tri- and tetra-substituted vinyl monomers are those with fluorine, like tetrafluoroethylene (CF2=CF2). The main cause of this reactivity pattern is the steric size of the substituents.
  28. 28. EXAMPLES OF ADDITION POLYMERIZATION • Polyethylene (PE)
  29. 29. • Polyvinyl Chloride (PVC) • The IUPAC name for polyvinyl chloride is poly(chloroethene) while for vinyl chloride (monomer) is chloroethene.
  30. 30. • Teflon (PTFE) • The IUPAC name for Teflon is poly(tetrafluoroethene), PTFE.
  31. 31. SUMMARY : POLYMERIZATION REACTIONS
  32. 32. APPLICATION • Polymeric materials are used in and on soil to improve aeration, provide mulch, and promote plant growth and health. Medicine • Many biomaterials, especially heart valve replacements and blood vessels, are made of polymers like Dacron, Teflon and polyurethane. Consumer Science • Plastic containers of all shapes and sizes are light weight and economically less expensive than the more traditional containers. Clothing, floor coverings, garbage disposal bags, and packaging are other polymer applications.
  33. 33. Industry • Automobile parts, windshields for fighter planes, pipes, tanks, packing materials, insulation, wood substitutes, adhesives, matrix for composites, and elastomers are all polymer applications used in the industrial market. Sports • Playground equipment, various balls, golf clubs, swimming pools, and protective helmets are often produced from polymers.
  34. 34. REFFERENCES • http://en.wikipedia.org/wiki/Polymerization#cite_note-3 • http://www.cliffsnotes.com/sciences/chemistry/organicchemistry-i/reactions-of-alkenes/alkenes-polymerization • http://www.engineeringtoolbox.com/polymer-propertiesd_1222.html • http://en.wikipedia.org/wiki/IUPAC_polymer_nomenclature • http://en.wikipedia.org/wiki/Condensation_polymer • http://www.files.chem.vt.edu/chem-dept/marand/Lecture5.pdf

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