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THE CHEMISTRY OF POLYMERS A guide for A level students

THE CHEMISTRY OF POLYMERS A guide for A level students. 2008 SPECIFICATIONS. KNOCKHARDY PUBLISHING. KNOCKHARDY PUBLISHING. POLYMERS. INTRODUCTION

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THE CHEMISTRY OF POLYMERS A guide for A level students

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  1. THE CHEMISTRY OF POLYMERS A guide for A level students 2008 SPECIFICATIONS KNOCKHARDY PUBLISHING

  2. KNOCKHARDY PUBLISHING POLYMERS INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... www.knockhardy.org.uk/sci.htm Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

  3. POLYMERS • CONTENTS • Prior knowledge • Types of polymerisation • Addition polymerisation • Polymerisation of propene • Condensation polymerisation • Peptides • Hydrolysis of peptides

  4. POLYMERS • Before you start it would be helpful to… • know the functional groups found in organic chemistry • know the arrangement of bonds around carbon atoms • recall and explain electrophilic addition reactions of alkenes

  5. POLYMERISATION GeneralA 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 CONDENSATIONmonomers join up the with expulsion of small molecules not all the original atoms are present in the polymer

  6. ADDITION POLYMERISATION • all the atoms in the monomer are used to form the polymer • occurs with alkenes • mechanism can be free radical or ionic

  7. POLYMERISATION OF ALKENES ADDITION POLYMERISATION Preparation Often 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 catalyst is a Ziegler-Natta catalyst (named after the scientists who developed it). Such catalysts are based on the compound TiCl4.

  8. POLYMERISATION OF ALKENES ADDITION POLYMERISATION Preparation Often 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 catalyst is a Ziegler-Natta catalyst (named after the scientists who developed it). Such catalysts are based on the compound TiCl4. Properties Physical vary with reaction conditions (pressure, temperature etc). Chemical 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.

  9. POLYMERISATION OF ALKENES ADDITION POLYMERISATION 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

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

  11. 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

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

  13. POLYMERISATION OF ALKENES SPOTTING THE MONOMER

  14. POLYMERISATION OF ALKENES SPOTTING THE MONOMER

  15. POLYMERISATION OF PROPENE - ANIMATION AN EXAMPLE OF ADDITION POLYMERISATION PROPENE MOLECULES DO NOT ALWAYS ADD IN A REGULAR WAY THERE ARE THREE BASIC MODES OF ADDITION ISOTACTIC SYNDIOTACTIC ATACTIC

  16. POLY(PROPENE) ISOTACTIC CH3 groups on same side - most desirable properties - highest melting point SYNDIOTACTIC CH3 groups alternate sided ATACTIC random most likely outcome

  17. CONDENSATION POLYMERS •monomers join up the with expulsion of small molecules • not all the original atoms are present in the polymer Examples polyamides (nylon) (kevlar) polyesters (terylene) (polylactic acid) peptides starch Synthesis reactions between diprotic carboxylic acids and diols diprotic carboxylic acids and diamines amino acids ESTER LINK AMIDE LINK

  18. POLYESTERS - TERYLENE Reagentsterephthalic acidHOOC-C6H4-COOH ethane-1,2-diolHOCH2CH2OH Reactionesterification Eliminatedwater Equationn HOCH2CH2OH + n HOOC-C6H4-COOH ——> -[OCH2CH2OOC(C6H4)CO] n- + n H2O

  19. POLYESTERS - TERYLENE Reagentsterephthalic acidHOOC-C6H4-COOH ethane-1,2-diolHOCH2CH2OH Reactionesterification Eliminatedwater Equationn HOCH2CH2OH + n HOOC-C6H4-COOH ——> -[OCH2CH2OOC(C6H4)CO] n- + n H2O Repeatunit— [-OCH2CH2OOC(C6H4)CO-] n — Productpoly(ethylene terephthalate)‘Terylene’, ‘Dacron’ Propertiescontains an ester link can be broken down by hydrolysis the C-O bond breaks behaves as an ester biodegradable Usesfabricsan ester link

  20. POLYESTERS – POLY(LACTIC ACID) Reagent 2-hydroxypropanoic acid (lactic acid) CH3CH(OH)COOH CARBOXYLIC ACID END ALCOHOL END

  21. POLYESTERS – POLY(LACTIC ACID) Reagent 2-hydroxypropanoic acid (lactic acid) CH3CH(OH)COOH Reactionesterification Eliminatedwater Equationn CH3CH(OH)COOH —> −[-OCH(CH3)CO-]n − + n H2O Productpoly(lactic acid) Repeatunit— [-OCH(CH3)CO-] — CARBOXYLIC ACID END ALCOHOL END

  22. POLYESTERS – POLY(LACTIC ACID) Reagent 2-hydroxypropanoic acid (lactic acid) CH3CH(OH)COOH Productpoly(lactic acid) Propertiescontains an ester link can be broken down by hydrolysis the C-O bond breaks behaves as an ester (hydrolysed at the ester link) biodegradable photobiodegradable (C=O absorbs radiation) Uses waste sacks and packaging disposable eating utensils internal stitches CARBOXYLIC ACID END ALCOHOL END

  23. POLYAMIDES – KEVLAR Reagents benzene-1,4-diamine benzene-1,4-dicarboxylic acid Repeatunit Propertiescontains an amide link Uses body armour

  24. POLYAMIDES - NYLON-6,6 Reagentshexanedioic acid hexane-1,6-diamine HOOC(CH2)4COOH H2N(CH2)6NH2 Mechanismaddition-elimination Eliminatedwater Equationn HOOC(CH2)4COOH + n H2N(CH2)6NH2 ——> -[NH(CH2)6NHOC(CH2)4CO] n- + n H2O

  25. POLYAMIDES - NYLON-6,6 Reagentshexanedioic acid hexane-1,6-diamine HOOC(CH2)4COOH H2N(CH2)6NH2 Mechanismaddition-elimination Eliminatedwater Equationn HOOC(CH2)4COOH + n H2N(CH2)6NH2 ——> -[NH(CH2)6NHOC(CH2)4CO] n- + n H2O Repeatunit—[-NH(CH2)6NHOC(CH2)4CO-]n— ProductNylon-6,6 two repeating units, each with 6 carbon atoms

  26. POLYAMIDES - NYLON-6,6 Propertiescontains 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

  27. PEPTIDES Reagentsamino acids EquationH2NCCH2COOH + H2NC(CH3)COOH ——> H2NCCH2CONHHC(CH3)COOH + H2O Productpeptide (the above shows the formation of a dipeptide) Eliminatedwater Mechanismaddition-elimination

  28. PEPTIDES Reagentsamino acids EquationH2NCCH2COOH + H2NC(CH3)COOH ——> H2NCCH2CONHHC(CH3)COOH + H2O 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 joined dipeptide 3 amino acids joined tripeptide many amino acids joined polypeptide a dipeptide

  29. HYDROLYSIS OF PEPTIDES Hydrolysis + H2O ——> HOOCCH2NH2 + HOOCCH(CH3)NH2 The acid and amine groups remain as they are Hydrolysis is much quicker if acidic or alkaline conditions are used. However, there is a slight variation in products.

  30. HYDROLYSIS OF PEPTIDES Hydrolysis + H2O ——> HOOCCH2NH2 + HOOCCH(CH3)NH2 The acid and amine groups remain as they are Acid hydrolysis + 2HCl ——> HOOCCH2NH3+Cl¯ + HOOCCH(CH3)NH3+Cl¯ The acid groups remain as they are and the amine groups are protonated

  31. HYDROLYSIS OF PEPTIDES Hydrolysis + H2O ——> HOOCCH2NH2 + HOOCCH(CH3)NH2 The acid and amine groups remain as they are Acid hydrolysis + 2HCl ——> HOOCCH2NH3+Cl¯ + HOOCCH(CH3)NH3+Cl¯ The acid groups remain as they are and the amine groups are protonated Base (alkaline) hydrolysis+ 2NaOH ——> Na+ ¯OOCCH2NH2 + Na+ ¯OOCCH(CH3)NH2 The acid groups become sodium salts and the amine groups remain as they are

  32. HYDROLYSIS OF PEPTIDES Hydrolysis + H2O ——> HOOCCH2NH2 + HOOCCH(CH3)NH2 The acid and amine groups remain as they are Acid hydrolysis + 2HCl ——> HOOCCH2NH3+Cl¯ + HOOCCH(CH3)NH3+Cl¯ The acid groups remain as they are and the amine groups are protonated Base (alkaline) hydrolysis+ 2NaOH ——> Na+ ¯OOCCH2NH2 + Na+ ¯OOCCH(CH3)NH2 The acid groups become sodium salts and the amine groups remain as they are

  33. 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

  34. THE CHEMISTRY OF POLYMERS THE END © 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

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