Polymer Molecules
Condensation and
Addition Polymers.
Proteins and Enzymes,
Index
Condensation polymers; starch, polyamides and polyesters
Proteins
Enzymes
Linear and cross-linked polymers
Specialised polymers
Consumption of plastic
History of Plastics
Condensation Polymers
Polymers are very large molecules made by joining small molecules called
monomers, into long chains or networks.
Condensation polymers are made from monomers with two functional
groups which can be the same or different.
Starch is made by polymerisation of about 300 glucose molecules
H
O
Glucose
O
H
H
O
O
H
H
O
Glucose
The adding together of monomers
to make a polymer is called
polymerisation.
O
O
Maltose
O
O
Starch
O
H
+
H2O
Polyesters and Polyamides
Polyesters are examples of condensation polymers and are formed when a
carboxylic acid monomer reacts with an alcohol monomer.
H
O
O
O
H
H
O
C
Diol
monomer
C
O
O
O
C
H
O
C
O
O
O
O
C
C
O
O
Diacid
monomer
Polyamides (eg Nylon and Kevlar) are formed when an amide link is formed
by the reaction of an amino functional group with a carboxyl group.
H
H N
Diamine
monomer
O
H
N
H
H
O
C
C
Diacid
monomer
O
O
H
H
O
N
C
Amide link
+ water
Condensation Polymers
HO
O
O
O
+
OH
O
HO
O
CH2
O
CH2 O
CH2 CH2 O H
O
Polyester, e.g. terylene
Polyesters are used as textiles and resins. The latter have 3D structures,
unlike textiles, which have a linear structure.
Polyamide, e.g. nylon, an important engineering plastic.
It’s strength due to hydrogen bonding between the linear polymer chains.
Engineering plastics are a group of plastics materials that exhibit
superior mechanical and thermal properties
H 2N
(CH )
2 6
H
O
N
C
(CH )
2 4
O
H
C
N
(CH )
2 6
H
O
N
C
O
(CH )
2 4
C
H
3
Protein Polymers
All proteins contain the elements C,O,H, N. They are condensation polymers,
made by amino acids linking together. An amine group of one molecule links
to the carboxyl group of another molecule to form an amide or peptide bond.
The body cannot make every type of amino acids that it needs.
So our diet must contain essential amino acids. (about 10 of them).
We synthesis the others.
Amino Acids
H R
O
H N C
C
R
O H
NH2CHCOOH
Most proteins contain
20+ different amino
acids
H
When R is Hydrogen, the amino acid is glycine (Gly) (aminoethanoic acid)
When R is CH3, the amino acid is alanine (Ala) (2-aminopropanoic acid)
Protein Polymers
H
H
N
C
H
O
O
H
H N
C
Amino acid
monomer
O
H
C
N
O
O
H
Peptide link
CH3
H
CH3
H2NCHCOOH + H2NCHCOOH + H2NCHCOOH
alanine
glycine
CH3
H
H2NCHC
NCHC
O
H
alanine
CH3
NCHCOOH
O
Tripeptide, ala-gly-ala
H
Polypeptide chain can have 10000
amino acids
Protein Digestion
Proteins are broken down during digestion.
Digestion involves the hydrolysis of proteins to form amino acids
R1
Protein
R2
R3
H2NCHC
HNCHC
O
O
HNCHC O
H
O
2 x H-O-H added and the peptide bond breaks here
Peptidase enzyme
R1
Amino
acids
R2
H2NCHC O H
O
HNCHC
H
O
R3
O H
HNCHC O H
H
O
Protein Structures
Some proteins are composed of a single polypeptide chain, but many consist
of two or more polypeptide chains.
Proteins are classified according to their shape into fibrous and globular
proteins.
Fibrous proteins
These have their polypeptide chains interwoven. The polypeptide chains are
held together by hydrogen bonding, between the N-H and the C=O groups.
This gives these proteins their properties of toughness, insolubility, and
resistance to change in pH and temperature. So they are found in skin,tissue,
(collagens), hair, nails (keratins).
Globular proteins
Proteins which operate within cells need to be soluble. The polypeptide chains
are coiled together in spherical shapes. E.g. Haemoglobin and many hormones.
e.g. Insulin, was the first protein structure to be worked out.
Enzymes are globular proteins.
Protein Structures
Silk is a typical example of a fibrous protein.
Silk
This view shows the
protein chains contain 2
different amino acids.
This view shows
the individual
atoms in the
protein chains.
Protein Structures
Albumen, in egg white, is a globular protein..
Albumen
backbone view
atom view
Protein Structures
Enzymes are globular proteins. The structure of amylase is
shown below.
Starch molecule in the enzyme’s active site.
Enzyme Activity
Enzymes catalyse chemical reactions in the body. Each
enzyme has a unique shape held together by many weak
bonds. Changes to pH and temperature can denature the
enzyme. This changes the enzymes shape stops it working
properly.
Narrow optimum range
Enzyme
activity
Temp or pH
The bonds that hold most biological enzymes
are broken around 60oC.
Enzyme Activity, Lock and Key
The critical part of an enzyme molecule is called its active
site.
This is where binding of the substrate to enzyme occurs and
where catalysis takes place.
Most enzymes have one active site per molecule.
Substrate
Enzyme
Enzyme Activity, Lock and Key
Substrate
Enzyme
Active site
Enzyme Activity, Lock and Key
The substrate becomes activated
Enzyme
Enzyme Activity, Lock and Key
The substrate becomes activated
Enzyme
Enzyme Activity, Lock and Key
The complex molecule splits
Enzyme
Enzyme Activity, Lock and Key
The complex molecule splits
Enzyme
Linear Addition Polymers
H
H
H
H
C
C
C
C
H
H
H
H
polythene
Under the right conditions ethene molecules can be
made to join together.
The double bond must be broken for this to happen
Polymerisation
The ethene molecule is called a monomer.
Adding monomers together makes a polymer, in this case,
Polythene. (a linear addition polymer)
H H
H H
H H
H H H H
H H
C
C
C
C
C
C
C
C
C C
C
C
H H H H H H H H H H H H
Polythene can be made photodegradable by putting some
C=O groups into the chain
Other Addition Polymers
By replacing a H in the ethene molecule, further addition
polymers can be made. Three monomers are shown:
F
F
C6H5
H
Cl
H
C
C
C
C
C
C
F
F
H
H
H
H
Tetrafluoroethene
(teflon)
Non-stick coating on
frying pans
Phenylethene
(Polystyrene)
Expanded foam
for packaging
Chloroethene
(P.V.C.)
Artificial leather
Cross-Linked Polymers
CH2
CH2
CH2
OH
H 2C
HO
OH
CH2
HO
CH2
CH2
H 2C
When polymer chains are
linked by covalent bonds
the polymer is then described
as cross linked.
CH2
CH2
HO
CH2
CH2
H 2C
Bakelite
The resulting cross-linked structure
means that the polymer is
hard, rigid and heat resistant.
It is a thermosetting plastic.
Specialised Polymers
Kevlar is an aromatic polyamide. Both monomers are aromatic.
O
N
O
H
H
O
N
N
O
N
H
H
H
O
N
O
Hydrogen bonding
N
H
The polymer chains are long, flat, and lined up in a regular pattern
held by hydrogen bonding. Used in bullet proof vests, ropes and fire
proof clothing.
Uses of Kevlar
Uses include:
– as a substitute for steel
– Fabric for windsurfing sails and protective
clothing
– Bullet proof vests and body armour
– Reinforcing fibre in composites, often with carbon
fibre.
Disadvantages of Kevlar fibres:
– they are difficult to cut
– It is much weaker in compression
– Very prone to UV degradation
Specialised Polymers
Poly(ethenol) is an addition polymer. It is made by converting an existing
polymer which has ester side groups with hydroxyl groups.
The polymer can be made to be water soluble, by controlling the amount
of ester exchange, 90% ester exchange is soluble in cold water. Soiled
hospital laundry can be collected in bags made from poly(ethenol).
CH3
C
CH3
O
O
C
O
CH
CH2
O
+ methanol
CH
CH2
Polyethenyl ethanoate
Ester exchange
H
H
O
O
CH
CH
CH2
CH2
Polyethenol (polyvinyl alcohol)
Both hydrogen bonding and van der Waals’ forces operate between
poly(ethenol) molecules. The stronger these forces the less soluble the
polymer. <90% of –OH replacement are soluble in cold water.
Specialised Polymers
• Most plastics are not biodegradable.
• Most polymers, including polyethylene, polypropylene,
polyamides and polycarbonate, are highly resistant to
microbial attack.
• Natural polymers are generally more biodegradable
than synthetic polymers.
• Polymers containing an ester linkage, especially
aliphatic polyesters, are potentially biodegradable
Biodegradable polymers include poly(lactic acid) (PLA)
which is made from the self-condensation of lactic acid.
PLA breaks down into lactic acid which can be metabolised
and has
found uses in, drug delivery systems and wound
.
healing. Biopol is another biodegradable plastic.
Specialised Polymers
Biopol
This plastic is biodegradable. This plastic is produced by the fermentation
of ethanoic and propanoic acids by bacteria. Biopol is therfore unsuitable
For foods requiring a long shelf life. High production costs and the
recycling of polymers has meant that Biopol has lost its importance.
HO
CH3
H
O
C
C
C
H
H
O
OH
CH3
H
O
C
C
C
H
H
+ HO
O
C2H5
H
O
C
C
C
H
H
C2H5
H
O
C
C
C
H
H
OH
O
Specialised Polymers
Poly(vinylcarbazole)
This polymer can conduct electricity when exposed to light. It is
widely used in photocopying machines as a replacement for
selenium, which is poisonous.
N
H
C
H
H
C
H
N
C
H
N
H
C
H
H
C
H
3
UK Consumption of Plastics by Type
L/LLDPE
19.3%
OTHERS
20.7%
UP Resin
1.8%
HDPE
11.3%
PET/PBT
5.5%
ABS/SAN
2.1%
PA
1%
EPS
1.2%
PVC
16%
PP
16.1%
PS
5.2%
47% of the polymer used is polyolefins, based on
ethylene or propylene
UK Consumption of Plastics by Market
Medical
2%
Others
18%
Packaging
38%
Transport
7%
Furn/House
7%
Electrical
6%
Construction
22%