Macromolecules 6m1w33

Macromolecules Chemistry @ MBCC Science 2

OBJECTIVES 4.1 describe the characteristics of addition polymerisation 4.2 describe the characteristics of condensation polymerisation 4.3 predict types of polymer formed from given monomers 4.4 deduce the repeat unit of a polymer 4.5 identify proteins as naturally occurring macromolecules 4.6 identify carbohydrates as naturally occurring macromolecules 4.7 illustrate the connection between carbohydrates and their monomers

Polymerization • Small molecules (monomers) repeatedly to one another to form a large molecule called a (polymer) • The process is known as polymerization • Two main types of polymerization processes: – Addition Polymerization – Condensation Polymerization

Polymers • Polymers are natural or synthetic • Natural polymers eg. starch, proteins, cellulose • Synthetic Polymers eg. polyethene, polyvinyl chloride

Addition Polymerisation • Unsaturated monomers with double or triple bonds are linked together to form polymers • eg. polyethene, polyvinyl chloride (PVC) and polytetrafluoroethene (PTFE) • Mechanism goes via a free radical chain reaction • Mechanism involves three stages: – Initiation, propagation, termination

Addition Polymerisation: Mechanism Initiation – Organic peroxide decomposes to form free radicals – Free radicals initiate chain reaction

Propagation – Free radical reacts with neutral monomer to form longer chain free radical – Long chain radical takes part in another propagation reaction causing a chain reaction

Termination – Two radicals combine with each other – Less common is a disproportionation reaction between two radicals

Repeat Units • Repeat Unit is the simplest structure which is repeated in the polymer • To deduce the structure of a monomer from a polymer – first find the repeat unit – next put back the original carbon-carbon double bond

Types of Addition Polymers Write short notes on the following types of polymers (page 326, Maraj and Samai) – Polyethene • Low density polyethene • High density polyethene

– Polyvinyl chlorides – Polytetrafluoroethene ** Notes should include (i) the monomer used, (ii) equation for the reaction including the repeat unit, (iii) reaction conditions and (iv) uses of the polymer

Types of Addition Polymers

Condensation Polymerisation • Monomers are ed together in a condensation reaction with the loss of a small molecule such as water • Product depends on the functional group present in the monomer • Monomers usually have multiple functional groups – Monomers with two functional groups form linear polymers – Monomers with more than two functional groups usually form polymers with crosslinkages

Types of Condensation Polymers • Condensation Polymers are classified according to the linkages formed between the monomers – Polyesters – Polyamides

• Condensation polymers may be: – Synthetic eg. Terylene, Nylon 6.6 – Natural eg. Proteins, Carbohydrates such as starch and cellulose

PolyEsters • May be formed from combining diacid with dialcohol • Ester linkage is formed • Eg. Terylene (or dacron) – Used to make clothing, curtains, draperies etc.

PolyAmide • May be formed from a diamine and diacids (or diacyl chlorides) • Amide linkage is formed – Water molecule is lost if diacid is used – HCl molecule is used if diacyl chloride is used

• Eg. Nylon 6.6 – An early substitute for silk – Similar to polyamides in silk – Stronger, more durable and cheaper than natural fibres – Used for clothing, nylon ropes, parachutes etc.

Proteins

Monomers are amino acids Water molecule lost when two amino acids link to form a dipeptide Many amino acids link to form a polypeptide Polypeptides further folds up into complex networks to form the 1 0, 20, 30 and 40 structure of proteins Different sequencing of the amino acids gives rise to different properties in proteins

Carbohydrates  Naturally occurring condensation polymers  Examples include: - monosaccharides such as glucose and fructose - Disaccharides such as maltose and sucrose - Polysaccharides such as starch and cellulose

 Monosaccharides are monomer units eg. glucose  Disaccharides and polysaccharides contain the ether (glycosidic) linkage  The open (straight chain) form of glucose exists in equilibrium with the ring (cyclic) form  Carbon 1 in glucose (sugars) is known as the anomeric carbon

Carbohydrates Maltose

Carbohydrates Starch

Carbohydrates Cellulose

Carbohydrates Difference between Starch and Cellulose

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