Transcript No Slide Title
THE CHEMISTRY OF POLYMERS A guide for A level students
2008 SPECIFICATIONS
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
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POLYMERS CONTENTS
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
General ADDITION
POLYMERISATION
A process in which small molecules called monomers join together into large molecules consisting of repeating units.
There are two basic types 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
ADDITION POLYMERISATION
•
all the atoms in the monomer are used to form the polymer
•
occurs with alkenes
•
mechanism can be free radical or ionic
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 TiCl 4 .
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 TiCl 4 .
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 .
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
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 n represents a large number ethene MONOMER poly(ethene) POLYMER
POLYMERISATION OF ALKENES
ADDITION POLYMERISATION The equation shows the original monomer and the repeating unit in the polymer n represents a large number ethene MONOMER poly(ethene) POLYMER
ETHENE
POLYMERISATION OF ALKENES
EXAMPLES OF ADDITION POLYMERISATION POLY(ETHENE) PROPENE POLY(PROPENE) CHLOROETHENE TETRAFLUOROETHENE 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 PROPENE MOLECULES DO NOT ALWAYS ADD IN A REGULAR WAY THERE ARE THREE BASIC MODES OF ADDITION ISOTACTIC SYNDIOTACTIC ATACTIC
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 Synthesis polyamides polyesters peptides starch (nylon) (terylene) (kevlar) (polylactic acid) reactions between diprotic carboxylic acids and diols diprotic carboxylic acids and diamines amino acids ESTER LINK AMIDE LINK
POLYESTERS TERYLENE Reagents Reaction terephthalic acid ethane-1,2-diol esterification HOOC-C 6 H 4 -COOH HOCH 2 CH 2 OH Eliminated water 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
POLYESTERS TERYLENE Reagents terephthalic acid ethane-1,2-diol esterification HOOC-C HOCH 2 6 CH H 2 4 -COOH OH Reaction Eliminated water 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 Repeat unit — [ -OCH 2 CH 2 O OC(C 6 H 4 )CO ] n — Product poly(ethylene terephthalate) ‘Terylene’, ‘Dacron’ Properties Uses contains an ester link can be broken down by hydrolysis the C-O bond breaks behaves as an ester biodegradable fabrics an ester link
Reagent ALCOHOL END POLYESTERS – POLY(LACTIC ACID) 2-hydroxypropanoic acid (
lactic acid
) CH 3 CH(OH)COOH CARBOXYLIC ACID END
Reagent ALCOHOL END POLYESTERS – POLY(LACTIC ACID) 2-hydroxypropanoic acid (
lactic acid
) CH 3 CH(OH)COOH CARBOXYLIC ACID END Reaction Eliminated Equation Product Repeat unit esterification water n CH 3 CH(OH)COOH —> −[-OCH(CH 3 )CO-] n − + n H 2 O poly(lactic acid) — [-OCH(CH 3 )CO-] —
Reagent ALCOHOL END POLYESTERS – POLY(LACTIC ACID) 2-hydroxypropanoic acid (
lactic acid
) CH 3 CH(OH)COOH CARBOXYLIC ACID END Product Properties Uses poly(lactic acid) contains 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) waste sacks and packaging disposable eating utensils internal stitches
Reagents POLYAMIDES – KEVLAR benzene-1,4-diamine benzene-1,4-dicarboxylic acid Repeat unit Properties Uses contains an amide link body armour
POLYAMIDES NYLON-6,6 Reagents Mechanism hexanedioic acid HOOC(CH 2 ) 4 COOH addition-elimination hexane-1,6-diamine H 2 N(CH 2 ) 6 NH 2 Eliminated Equation water 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
POLYAMIDES NYLON-6,6 Reagents Mechanism hexanedioic acid HOOC(CH 2 ) 4 COOH addition-elimination hexane-1,6-diamine H 2 N(CH 2 ) 6 NH 2 Eliminated water Equation Repeat unit 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 —[ -NH(CH 2 ) 6 NH OC(CH 2 ) 4 CO ] n — Product Nylon-6,6 two repeating units, each with 6 carbon atoms
Properties Uses POLYAMIDES NYLON-6,6 contains 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 fibres and ropes
PEPTIDES Reagents Equation Product Eliminated Mechanism amino acids H 2 NCCH 2 COOH + H 2 NC(CH 3 )COOH ——> H 2 NCCH 2 CONH HC(CH 3 )COOH + H 2 O peptide (the above shows the formation of a dipeptide) water addition-elimination
PEPTIDES Reagents Equation Product Eliminated Mechanism amino acids H 2 NCCH 2 COOH + H 2 NC(CH 3 )COOH ——> H 2 NCCH 2 CONH HC(CH 3 )COOH + H 2 O peptide (the above shows the formation of a dipeptide) water addition-elimination Amino acids join together via an amide or peptide link a dipeptide 2 amino acids joined 3 amino acids joined many amino acids joined dipeptide tripeptide polypeptide
HYDROLYSIS OF PEPTIDES Hydrolysis
+ H 2 O ——> HOOCCH 2 NH 2 + HOOCCH(CH 3 )NH 2
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.
HYDROLYSIS OF PEPTIDES Hydrolysis
+ H 2 O ——> HOOCCH 2 NH 2 + HOOCCH(CH 3 )NH 2
The acid and amine groups remain as they are Acid hydrolysis
+ 2HC
l
——> HOOCCH 2 NH 3 + C
l
¯ + HOOCCH(CH 3 )NH 3 + C
l
¯
The acid groups remain as they are and the amine groups are protonated
HYDROLYSIS OF PEPTIDES Hydrolysis
+ H 2 O ——> HOOCCH 2 NH 2 + HOOCCH(CH 3 )NH 2
The acid and amine groups remain as they are Acid hydrolysis
+ 2HC
l
——> HOOCCH 2 NH 3 + C
l
¯ + HOOCCH(CH 3 )NH 3 + C
l
¯
The acid groups remain as they are and the amine groups are protonated Base (alkaline) hydrolysis
+ 2NaOH ——> Na+ ¯OOCCH 2 NH 2 + Na+ ¯OOCCH(CH 3 )NH 2
The acid groups become sodium salts and the amine groups remain as they are
HYDROLYSIS OF PEPTIDES Hydrolysis
+ H 2 O ——> HOOCCH 2 NH 2 + HOOCCH(CH 3 )NH 2
The acid and amine groups remain as they are Acid hydrolysis
+ 2HC
l
——> HOOCCH 2 NH 3 + C
l
¯ + HOOCCH(CH 3 )NH 3 + C
l
¯
The acid groups remain as they are and the amine groups are protonated Base (alkaline) hydrolysis
+ 2NaOH ——> Na+ ¯OOCCH 2 NH 2 + Na+ ¯OOCCH(CH 3 )NH 2
The acid groups become sodium salts and the amine groups remain as they are
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
THE CHEMISTRY OF POLYMERS THE END
© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING