THE CHEMISTRY
OF POLYMERS
A guide for A level students
POLYMERS
CONTENTS
• Prior knowledge
• Types of polymerisation
• Addition polymerisation
• Condensation polymerisation
• Peptides
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
POLYMERIZATION OF ALKENES
= addition polymers = POLYALKENES
repeated addition of 1000’s of alkene molecules
(each called a MONOMER)
to each other to form a single macromolecule
(called the POLYMER).
In general, polymerisation is aided by use of :
1. High pressure : many molecules one
2. High temperature : increase rate even though yield
reduced because exothermic
3. Catalyst : acceptable rate at lower temperature
X Monomer Polymer
X H
H Ethene Poly(ethene)
n C C
CH3 Propene Poly(propene)
H H
Poly-
Cl Chloroethene
(chloroethene)
X H X H X H X H
C C C C C C C C
H H H H H H H H etc
Repeat unit of polymer
POLYMERISATION
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
ADDITION POLYMERISATION
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.
Cl H Chloroethene monomer
n C C
Poly(chloroethene)
H H “PVC”
Cl H Cl H Cl H Cl H
C C C C C C C C
H H H H H H H H etc
“Plastic” wallets and
carrier bags are often
made from PVC PVC as a leather substitute
F F Tetrafluoroethene monomer
n C C
Poly(tetrafluoroethene)
F F “PTFE”
F F F F F F F F
C C C C C C C C
F F F F F F F F etc
Some uses of PTFE
Non-stick coating for pans
Insulating tapes
Low friction coating for
surgical sutures
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 ethene poly(ethene)
large number
MONOMER POLYMER
POLYMERISATION OF ALKENES
ADDITION POLYMERISATION
The equation shows the original monomer and the repeating unit in the polymer
n represents a ethene poly(ethene)
large number
MONOMER POLYMER
POLYMERISATION OF ALKENES
EXAMPLES OF ADDITION POLYMERISATION
ETHENE POLY(ETHENE)
PROPENE POLY(PROPENE)
CHLOROETHENE POLY(CHLOROETHENE)
POLYVINYLCHLORIDE PVC
TETRAFLUOROETHENE POLY(TETRAFLUOROETHENE)
PTFE “Teflon”
Addition polymers are usually Non-Biodegradable
What is this?
It refers to the inability of a substance to be broken down by
natural organisms such as bacteria, fungi, insects etc. It will
retain its form for an extended period of time, even when
left exposed to the air or buried.
Why is this?
C-C bonds are very strong and not easily broken
Landfill sites are sometimes are filled to capacity because of the amount of
non-biodegradable materials dumped!
Using them as fuels or recycling them is the preferred treatment for non-
biodegradable polymers!
POLYMERISATION OF ALKENES
SPOTTING THE MONOMER
POLYMERISATION OF ALKENES
SPOTTING THE MONOMER
Condensation polymerisation
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
POLYESTERS - TERYLENE
Reagents terephthalic acid HOOC-C6H4-COOH
ethane-1,2-diol HOCH2CH2OH
Reaction esterification
Eliminated water
Equation
n HOCH2CH2OH + n HOOC-C6H4-COOH ——> H-[OCH2CH2OOC(C6H4)CO]n-OH + n H2O
POLYESTERS - TERYLENE
Reagents terephthalic acid HOOC-C6H4-COOH
ethane-1,2-diol HOCH2CH2OH
Reaction esterification
Eliminated water
Equation n HOCH2CH2OH + n HOOC-C6H4-COOH ——> H-[OCH2CH2OOC(C6H4)CO]n-OH + n
H2O
Repeat unit — [-OCH2CH2OOC(C6H4)CO-] n —
Product poly(ethylene terephthalate) ‘Terylene’, ‘Dacron’, PET
Properties contains an ester link
can be broken down by hydrolysis
the C-O bond breaks
behaves as an ester
biodegradable
Uses fabrics , bottles an ester link
POLYESTERS – POLY(LACTIC ACID)
Reagent 2-hydroxypropanoic acid (lactic acid)
CH3CH(OH)COOH
ALCOHOL CARBOXYLIC ACID
END END
POLYESTERS – POLY(LACTIC ACID)
Reagent 2-hydroxypropanoic acid (lactic acid)
CH3CH(OH)COOH
ALCOHOL CARBOXYLIC ACID
END END
Reaction esterification
Eliminated water
Equation n CH3CH(OH)COOH —> −[-OCH(CH3)CO-]n − + n H2O
Product poly(lactic acid)
Repeat unit — [-OCH(CH3)CO-] —
POLYESTERS – POLY(LACTIC ACID)
Reagent 2-hydroxypropanoic acid (lactic acid)
CH3CH(OH)COOH
ALCOHOL CARBOXYLIC ACID
END END
Product poly(lactic acid)
Properties 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)
Uses waste sacks and packaging
disposable eating utensils
internal stitches
POLYAMIDES – KEVLAR
Reagents benzene-1,4-diamine benzene-1,4-dicarboxylic acid
Repeat unit
Properties contains an amide link
Uses body armour
POLYAMIDES - NYLON-6,6
Reagents hexanedioic acid hexane-1,6-diamine
HOOC(CH2)4COOH H2N(CH2)6NH2
Mechanism addition-elimination
Eliminated water
Equation n HOOC(CH2)4COOH + n H2N(CH2)6NH2 —> H-[NH(CH2)6NHOC(CH2)4CO] n-OH + n
H2O
POLYAMIDES - NYLON-6,6
Reagents hexanedioic acid hexane-1,6-diamine
HOOC(CH2)4COOH H2N(CH2)6NH2
Mechanism addition-elimination
Eliminated water
Equation n HOOC(CH2)4COOH + n H2N(CH2)6NH2 —> H-[NH(CH2)6NHOC(CH2)4CO] n-OH + n
H2O
Repeat unit —[-NH(CH2)6NHOC(CH2)4CO-]n—
Product Nylon-6,6two repeating units, each with 6 carbon atoms
POLYAMIDES - NYLON-6,6
Properties 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
Uses fibres and ropes
PEPTIDES
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
PEPTIDES
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
a dipeptide
2 amino acids joined dipeptide
3 amino acids joined tripeptide
many amino acids joined polypeptide
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
