1. THE CHEMISTRY OF POLYMERS A guide for A level students KNOCKHARDY PUBLISHING

2. CONTENTS Prior knowledge Types of polymerisation Addition polymerisation Polymerisation of propene Condensation polymerisation Peptides Check list POLYMERS

3. General A process in which small molecules called monomers join together into large molecules consisting of repeating units. There are two basic types ADDITION all the atoms in the monomer are used to form the polymer CONDENSATION monomers join up the with expulsion of small molecules not all the original atoms are present in the polymer POLYMERISATION

4. all the atoms in the monomer are used to form the polymer occurs with alkenes mechanism is free radical ADDITION POLYMERISATION

5. Preparation Many are prepared by a free radical process involving high pressure, high temperature and a catalyst. The catalyst is usually a substance (e.g. an organic peroxide) which readily breaks up to form radicals which initiate a chain reaction. Another famous type of catalyst is a Ziegler-Natta catalyst (named after the scientists who developed it). Such catalysts are based on the compound TiCl 4. Properties Physical varied by changing the reaction conditions (pressure, temperature etc). Chemical have chemical properties based on the functional groups in their structure. poly(ethene) is typical; it is fairly inert as it is basically a very large alkane. This means it is resistant to chemical attack and non-biodegradable. POLYMERISATION OF ALKENES ADDITION POLYMERISATION

6. POLYMERISATION OF ALKENES Process during polymerisation, an alkene undergoes an addition reaction with itself all the atoms in the original alkenes are used to form the polymer long hydrocarbon chains are formed ADDITION POLYMERISATION the equation shows the original monomer and the repeating unit in the polymer ethene poly(ethene) MONOMER POLYMER n represents a large number

7. POLYMERISATION OF ALKENES ADDITION POLYMERISATION the equation shows the original monomer and the repeating unit in the polymer ethene poly(ethene) MONOMER POLYMER n represents a large number

8. POLYMERISATION OF ALKENES ETHENE EXAMPLES OF ADDITION POLYMERISATION PROPENE TETRAFLUOROETHENE CHLOROETHENE POLY(ETHENE) POLY(PROPENE) POLY(CHLOROETHENE) POLYVINYLCHLORIDE PVC POLY(TETRAFLUOROETHENE) PTFE “Teflon”

9. POLYMERISATION OF ALKENES SPOTTING THE MONOMER

10. POLYMERISATION OF ALKENES SPOTTING THE MONOMER

11. POLYMERISATION OF PROPENE - ANIMATION AN EXAMPLE OF ADDITION POLYMERISATION ISOTACTIC SYNDIOTACTIC ATACTIC PROPENE MOLECULES DO NOT ALWAYS ADD IN A REGULAR WAY Animation may not work in earlier versions of Powerpoint THERE ARE THREE BASIC MODES OF ADDITION

12. POLY(PROPENE) ISOTACTIC CH 3 groups on same side - most desirable properties - highest melting point SYNDIOTACTIC CH 3 groups alternate sided ATACTIC random most likely outcome

13. CONDENSATION POLYMERS monomers join up the with expulsion of small molecules not all the original atoms are present in the polymer Examplespolyamides(nylon) polyesters(terylene) peptides starch Synthesis reactions between di-carboxylic acids and diols di-carboxylic acids and diamines amino acids ESTER LINKAMIDE LINK

14. POLYESTERS - TERYLENE Reagentsterephthalic acidHOOC-C 6 H 4 -COOH ethane-1,2-diolHOCH 2 CH 2 OH Equation n HOCH 2 CH 2 OH + n HOOC-C 6 H 4 -COOH ——> -[OCH 2 CH 2 OOC(C 6 H 4 )CO] n - + n H 2 O Productpoly(ethylene terephthalate)‘Terylene’, ‘Dacron’ Repeat unit— [-OCH 2 CH 2 OOC(C 6 H 4 )CO-] n — Eliminatedwater Reactionesterification Propertiescontain an ester link can be broken down by hydrolysis the C-O bond breaks behaves as an ester biodegradable Usesfabrics

15. POLYAMIDES - NYLON-6,6 Reagentshexanedioic acidHOOC(CH 2 ) 4 COOH hexane-1,6-diamineH 2 N(CH 2 ) 6 NH 2 Equation n HOOC(CH 2 ) 4 COOH + n H 2 N(CH 2 ) 6 NH 2 ——> -[NH(CH 2 ) 6 NHOC(CH 2 ) 4 CO] n - + n H 2 O ProductNylon-6,6two repeating units, each with 6 carbon atoms Repeat unit—[-NH(CH 2 ) 6 NHOC(CH 2 ) 4 CO-] n — Eliminatedwater Mechanismaddition-elimination Propertiescontain a peptide (or amide) link can be broken down by hydrolysis the C-N bond breaks behave as amides biodegradable can be spun into fibres for strength Usesfibres and ropes

16. PEPTIDES Reagentsamino acids Equation H 2 NCCH 2 COOH + H 2 NC(CH 3 )COOH ——> H 2 NCCH 2 CONHHC(CH 3 )COOH + H 2 O Productpeptide (the above shows the formation of a dipeptide) Eliminatedwater Mechanismaddition-elimination Amino acids join together via an amide or peptide link 2 amino acids joineddipeptide 3 amino acids joinedtripeptide many amino acids joinedpolypeptide a dipeptide

17. PROTEINS polypeptides with large relative molecular masses (>10000) chains can be lined up with each other the C=O and N-H bonds are polar due to a difference in electronegativity hydrogen bonding exists between chains dotted lines ---------- represent hydrogen bonding

18. REVISION CHECK What should you be able to do? Recall the two main types of polymerisation Explain and understand how alkenes undergo addition polymerisation Work out the repeating unit in addition polymers Recall and understand the different types of structures of poly(propene) Recall the properties of some common polymers Recall that polyesters and polyamides are formed by condensation polymerisation Recall the properties and uses of some condensation polymers Work out the repeating unit in condensation polymers Recall that peptides are examples of condensation polymers

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21. THE CHEMISTRY OF POLYMERS THE END © 2003 JONATHAN HOPTON & KNOCKHARDY PUBLISHING