Transcript POLYMER CHEMISTRY

POLYMER
CHEMISTRY
Natural and Synthetic Polymers
• Polymers are made up of many (poly)
repeating units (mer). Simple polymers are
made up of single monomers joined
together in either addition or condensation
polymerisation.
Addition Polymers
•
•
•
•
•
•
•
•
•
•
•
•
•
In addition polymers the monomers contain double bonds which are broken
to join small molecules together in one long chain.
Polythene: made from ethene
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
ethene
polyethene
Other addition polymers:
Polyvinyl chloride (PVC) and polystyrene are addition polymers, like
polythene. The general equation for the formation of addition polymers is:
H Z
H Z H Z H Z H Z
n C C
~C C C C C C C C~
H H
H H H H H H H H
monomer
polymer
in PVC Z = Cl, in polypropene Z = CH3 and in polystyrene Z =
What is a Polymer?
Condensation Polymers Polyesters
• Esters are formed when an alcohol reacts with
either a carboxylic acid or an acid chloride.
Polyesters are made by reacting “double-ended”
molecules such as a diol or dicarboxylic acid.
HOOC X
COOH + HO Y OH
dicarboxylic acid
diol
~ OOC X COO Y OOC X COO Y~
polyester
+ 2H2O
• The most important polyester is terylene, made
from the esterification of ethane-1,2-diol and
benzene-1,4-dicarboxylic acid.
Condensation Polymers Polyamides
• Polyamides may be made by combining a
diamine and a dicarboxylic acid or acid
chloride. Nylon, the first synthetic fibre is a
polyamide. It was developed in the 1930’s
as a cheap alternative to silk.
Other Monomers – Kevlar and
Polystyrene
Natural Polymers - Proteins
glycine
• Proteins are polymers made from
amino acid monomers. Each amino
acid contains the NH2 group of an
amine and the COOH group of an
acid.
• The simplest amino acid is glycine.
What is its formula? What is its
IUPAC name?
• Apart from glycine, all amino acids
have a chiral carbon
(one with four different groups on it),
and therefore form optical isomers.
Normally only one optical isomer is
useful in our bodies.
alanine
Proteins - continued
• All the amino acids in proteins have the –NH2
group joined to the same carbon as the -COOH
group. There are 20 amino acids involved in
proteins required by humans.
• Eight of these cannot be made in our bodies and
must be included in the diet. These are known
as essential amino acids.
• In proteins, amino acids join together by
condensation polymerisation.
H
H
Protein continued
• Since each amino acid contains two active sites for the
polymerisation reaction, they can be assembled in any
order, providing an extremely large number of different
protein molecules. Most common proteins contain about
100 amino acids.
• The bond that joins the amino acids together is called a
peptide link.
R-C-NH-R
O
the peptide link
• When the protein is digested, the polymer is hydrolysed
in exactly the same way that amides are. The acid in the
stomach breaks the peptide link.
Natural Polymers – Starch and
Cellulose
• Glucose is the simplest sugar. It
normally forms a 6-membered ring.
• There are two forms of the glucose
ring,  and . In  glucose this OH
group is below the plane of the ring
and in  glucose it is above the
plane. The ring can be broken to
form a chain form of the molecule
which shows that glucose is an
aldehyde and hence gains its name
of a ‘reducing sugar’.
• http://www.biotopics.co.uk/as/glucos
e2.html
Starch
• Starch is a condensation polymer made from
glucose monomers. A molecule of water is lost
at every join.
• When starch is hydrolysed, either by the action
of enzymes or acid, water is added to reform the
glucose monomers.
• Soluble starch (amylose) is formed from long
straight chains of -glucose molecules, while the
insoluble forms of starch e.g. amylopectin and
glycogen are branched linear polymers of glucose.
Amylose structure
Glycogen and Amylopectin
Glycogen has 1-6 branching, as does amylopectin,
but glycogen has more branching
Cellulose
• In cellulose, the -glucose molecules are arranged in long, straight
chains, but the arrangement is a little different from that of soluble
starch, and it allows the chains to hydrogen bond with each other.
• The chains combine to form long fibres which resist most solvents
and chemicals. Only a few specialised bacteria have the ability to
hydrolyse cellulose. Without those bacteria in their stomachs grasseating animals such as cows and sheep would starve.
• In cellulose the glucoside links alternate above and below the plane
of the molecule.
• In starch they are all on the same side.
Cellulose
THE END