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THE CHEMISTRYTHE CHEMISTRYOF POLYMERSOF POLYMERS
A guide for A level studentsA guide for A level students
KNOCKHARDY PUBLISHINGKNOCKHARDY 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
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POLYMERSPOLYMERSKNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
CONTENTS
• Prior knowledge
• Types of polymerisation
• Addition polymerisation
• Polymerisation of propene
• Condensation polymerisation
• Peptides
• Check list
POLYMERSPOLYMERS
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
POLYMERSPOLYMERS
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
POLYMERISATIONPOLYMERISATION
• all the atoms in the monomer are used to form the polymer
• occurs with alkenes
• mechanism can be free radical or ionic
ADDITION POLYMERISATIONADDITION 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 TiCl4.
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 ALKENESPOLYMERISATION OF ALKENES
ADDITION POLYMERISATION
POLYMERISATION OF ALKENESPOLYMERISATION 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 ALKENESPOLYMERISATION 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 ALKENESPOLYMERISATION OF ALKENES
ETHENE
EXAMPLES OF ADDITION POLYMERISATION
PROPENE
TETRAFLUOROETHENE
CHLOROETHENE
POLY(ETHENE)
POLY(PROPENE)
POLY(CHLOROETHENE)
POLYVINYLCHLORIDE PVC
POLY(TETRAFLUOROETHENE)
PTFE “Teflon”
POLYMERISATION OF ALKENESPOLYMERISATION OF ALKENES
SPOTTING THE MONOMER
POLYMERISATION OF ALKENESPOLYMERISATION OF ALKENES
SPOTTING THE MONOMER
POLYMERISATION OF PROPENE - ANIMATIONPOLYMERISATION OF PROPENE - ANIMATION
AN EXAMPLE OF ADDITION POLYMERISATION
ISOTACTICSYNDIOTACTICATACTIC
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)POLY(PROPENE)
ISOTACTICCH3 groups on same side
- most desirable properties- highest melting point
SYNDIOTACTICCH3 groups alternate sided
ATACTICrandommost likely outcome
CONDENSATION POLYMERSCONDENSATION 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)peptidesstarch
Synthesis reactions between diprotic carboxylic acids and diols diprotic carboxylic acids and diamines amino acids
ESTER LINK AMIDE LINK
POLYESTERS - POLYESTERS - TERYLENETERYLENE
Reagents terephthalic acid HOOC-C6H4-COOHethane-1,2-diol HOCH2CH2OH
Equation n HOCH2CH2OH + n HOOC-C6H4-COOH ——> -[OCH2CH2OOC(C6H4)CO] n - + n H2O
Product poly(ethylene terephthalate) ‘Terylene’, ‘Dacron’
Repeat unit — [-OCH2CH2OOC(C6H4)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 - POLYAMIDES - NYLON-6,6NYLON-6,6
Reagents hexanedioic acid HOOC(CH2)4COOHhexane-1,6-diamine H2N(CH2)6NH2
Equation n HOOC(CH2)4COOH + n H2N(CH2)6NH2 ——> -[NH(CH2)6NHOC(CH2)4CO] n- + n H2O
Product Nylon-6,6two repeating units, each with 6 carbon atoms
Repeat unit —[-NH(CH2)6NHOC(CH2)4CO-]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
PEPTIDESPEPTIDES
Reagents amino acids
Equation H2NCCH2COOH + H2NC(CH3)COOH ——> H2NCCH2CONHHC(CH3)COOH + H2O
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
PROTEINSPROTEINS
• 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 CHECKREVISION 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? CAN YOU DO ALL OF THESE? YES YES NONO
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THE CHEMISTRYTHE CHEMISTRYOF POLYMERSOF POLYMERS
THE ENDTHE END
© 2003 JONATHAN HOPTON & KNOCKHARDY PUBLISHING© 2003 JONATHAN HOPTON & KNOCKHARDY PUBLISHING