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THE CHEMISTRY OF POLYMERS A guide for A level students KNOCKHARDY PUBLISHING
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 POLYMERS KNOCKHARDY PUBLISHING
Types of polymerisation
Polymerisation of propene
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
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
• all the atoms in the monomer are used to form the polymer • occurs with alkenes • mechanism can be free radical or ionic ADDITION POLYMERISATION
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 whichinitiate 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
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
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
POLYMERISATION OF ALKENES ETHENE EXAMPLES OF ADDITION POLYMERISATION PROPENE TETRAFLUOROETHENE CHLOROETHENE POLY(ETHENE) POLY(PROPENE) POLY(CHLOROETHENE) POLYVINYLCHLORIDE PVC POLY(TETRAFLUOROETHENE) PTFE “Teflon”
POLYMERISATION OF ALKENES SPOTTING THE MONOMER
POLYMERISATION OF ALKENES SPOTTING THE MONOMER
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
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
CONDENSATION POLYMERS • monomers join up the with expulsion of small molecules • not all the original atoms are present in the polymer Examples polyamides (nylon) polyesters (terylene) peptides starch Synthesis reactions between diprotic carboxylic acids and diols diprotic carboxylic acids and diamines amino acids ESTER LINK AMIDE LINK
POLYESTERS - TERYLENE Reagents terephthalic acid HOOC-C 6 H 4 -COOH ethane-1,2-diol HOCH 2 CH 2 OH Equation n HOCH 2 CH 2 OH + n HOOC-C 6 H 4 -COOH ——> -[ OCH 2 CH 2 O OC(C 6 H 4 )CO ] n - + n H 2 O Product poly(ethylene terephthalate) ‘Terylene’, ‘Dacron’ Repeat unit — [ -OCH 2 CH 2 O OC(C 6 H 4 )CO- ] n — Eliminated water Reaction esterification Properties contain an ester link can be broken down by hydrolysis the C-O bond breaks behaves as an ester biodegradable Uses fabrics
POLYAMIDES - NYLON-6,6 Reagents hexanedioic acid HOOC(CH 2 ) 4 COOH hexane-1,6-diamine H 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 NH OC(CH 2 ) 4 CO ] n - + n H 2 O Product Nylon-6,6 two repeating units, each with 6 carbon atoms Repeat unit —[ -NH(CH 2 ) 6 NH OC(CH 2 ) 4 CO- ] n — Eliminated water Mechanism addition-elimination Properties contain 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 Uses fibres and ropes
PEPTIDES Reagents amino acids Equation H 2 NCCH 2 COOH + H 2 NC(CH 3 )COOH ——> H 2 NCCH 2 CONH HC(CH 3 )COOH + H 2 O Product peptide (the above shows the formation of a dipeptide) Eliminated water Mechanism addition-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
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
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 CAN YOU DO ALL OF THESE? YES NO
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