Macromolecules PDF

Organic Macromolecules Macromolecules are large molecules which are made up from small units by a chemical reaction There are two classes of macromolecules: POLYMERISATION Polymerisation is the process in which many small molecules (monomers) chemically react together to form a...

Organic Macromolecules Macromolecules are large molecules which are made up from small units by a chemical reaction There are two classes of macromolecules: POLYMERISATION Polymerisation is the process in which many small molecules (monomers) chemically react together to form a large molecule (polymer). Types of Polymerisation There are two types of polymerisation 1Addition polymerisation 2 Condensation polymerisation ADDITION POLYMERISATION  Addition polymerisation is a process by which many small molecules (monomers) are added onto one another to form one large molecule (polymer).  ONLY unsaturated compounds (i.e. compounds containing a double bond between the carbon atoms) can undergo addition polymerisation.  The double bonds between carbon atoms of monomer are converted to single bonds.  In addition polymerisation, the monomer and the repeating unit of the polymer have the SAME molecular formula, empirical formula and relative molecular mass.  The percentage by mass of elements in monomers and polymer remain the same.  The melting point, boiling point and density of the polymer are different from the monomer.  Example of Addition Polymerisation Formation of Poly(ethene)  Poly(ethene) is an addition polymer formed by the addition polymerisation of ethene monomers at a specific temperature and pressure. Oxygen is used as a catalyst. H H H H n = number of ethene n C C C C molecules H H H H n ethene poly(ethene) monomer polymer  The above structure can be simplified and written as [-CH 2 – CH2-]n Example of Addition Polymers and Their Uses..  Addition polymers can be homopolymers. containing just one type of monomer. For example poly(propene) from the monomer propene,  Addition polymers can also be copolymers containing two or more different types of monomers. For example, the following polymer was made from the monomers styrene and methyl methacrylate……..poly methyl 1 methacrylate formed.  CONDENSATION POLYMERISATION  Condensation polymerisation is a process where two monomers react together to produce a large molecule, with the elimination of a small molecule like water (H2O), ammonia (NH3), hydrogen chloride (HCl) etc.  The two monomers can be the same as in starch or different as in nylon, proteins, and terylene.  Condensation polymers can be synthetic like nylon and terylene or natural like starch and proteins.  The molecular formula and relative molecular mass of monomers and the repeating unit of polymers are different.  Two synthetic condensation polymers will be discussed. They are nylon and terylene.   To simplify the structure a box is used to NYLON represent the carbon- hydrogen  Nylon is a condensation polymer formed from the two chain. The monomers; atoms in the box (carbon-hydrogen chain) do not undergo any chemical change during the polymerisation process. Only the functional groups take part in the reaction. Formation of Nylon Properties and Uses of Nylon Nylon is strong yet light. It can be stretched without breaking. Nylon is made into fibres to produce strong ropes, fishing lines and carpets. It is woven into cloth to manufacture raincoats, parachutes and tents. It is used to make curtain rail fittings cupboard hinges and gear wheels.  TERYLENE Formation of Terylene Properties and Uses of Terylene Terylene is made into fibres which are woven into cloth. This polymer lasts longer than cotton. It is easier to wash and dry. Therefore polyester is used widely to produce clothes such as T- shirts. Terylene can also be used to produce  PLASTICS All man made polymers are plastics. Some common examples are nylon and poly(ethene). There are several advantages of using plastics:  Plastics can be easily moulded into a variety of shapes.  They are strong but light.  They are considerably cheap.  Plastics are corrosion resistant (do not corrode) and durable (long lasting).  They can be made in different forms (e.g. films, fibres, rigid solids, solid foam). However there are several disadvantages of using plastics..  Since plastics are carbon compounds, they can burn easily causing fire risk in buildings.  Disposing plastics is a major problem because it is corrosion resistant. Most plastics are non- biodegradable. That is, they are not decomposed by bacteria in the ground.  Plastics are often disposed of by burning. However this produces toxic gases which cause health hazards.  Many sea-animals die each year as a result of eating plastic or getting tangled in plastic nets. NATURAL MACRO MOLECULES  All living organisms contain natural macromolecules, such as proteins, starch and fats.  Most of these substances are large molecules made from smaller molecules. For example proteins are made from amino acids.  Most carbohydrates and all proteins are polymers. However fats are not polymers.   PROTEINS  Proteins are natural condensation polymers made up from monomers called amino acids. Proteins contain the elements carbon, hydrogen, nitrogen and oxygen.  There are many types of amino acids but only about 20 are found in nature.  Each amino acid monomer has two functional groups;  the amine group (-NH2) and the carboxylic acid group (-COOH)  The amino acid monomer can be represented as: Formation of Proteins  When amino acids combine, the –OH from the carboxyl group (-COOH) of one amino acid combines with a –H from the amino group (-NH2) of the next amino acid, to form water molecules which are then eliminated.  The peptide link found in proteins is the same as the amide linkage found in nylon.  When amino acids combine to form a long chain, the polymer formed is a polypeptide chain. Thus proteins Hydrolysis of Proteins.