4. macromolecules

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Macromolecules Chemistry @ MBCC Science 2

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Macromolecules

MacromoleculesChemistry @ MBCCScience 2OBJECTIVES4.1 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

PolymerizationSmall molecules (monomers) join repeatedly to one another to form a large molecule called a (polymer)The process is known as polymerizationTwo main types of polymerization processes:Addition PolymerizationCondensation PolymerizationPolymersPolymers are natural or syntheticNatural polymers eg. starch, proteins, celluloseSynthetic Polymers eg. polyethene, polyvinyl chloride

Addition PolymerisationUnsaturated 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 reactionMechanism involves three stages:Initiation, propagation, termination

Addition Polymerisation: MechanismInitiationOrganic peroxide decomposes to form free radicalsFree radicals initiate chain reactionPropagationFree radical reacts with neutral monomer to form longer chain free radicalLong chain radical takes part in another propagation reaction causing a chain reaction TerminationTwo radicals combine with each otherLess common is a disproportionation reaction between two radicals

Repeat UnitsRepeat Unit is the simplest structure which is repeated in the polymerTo deduce the structure of a monomer from a polymerfirst find the repeat unitnext put back the original carbon-carbon double bond

Types of Addition PolymersWrite short notes on the following types of polymers (page 326, Maraj and Samai)PolyetheneLow density polyetheneHigh density polyethenePolyvinyl chloridesPolytetrafluoroethene** Notes should include (i) the monomer used, (ii) equation for the reaction including the repeat unit, (iii) reaction conditions and (iv) uses of the polymerTypes of Addition Polymers

Condensation PolymerisationMonomers are joined together in a condensation reaction with the loss of a small molecule such as waterProduct depends on the functional group present in the monomerMonomers usually have multiple functional groups Monomers with two functional groups form linear polymersMonomers with more than two functional groups usually form polymers with crosslinkages

Types of Condensation PolymersCondensation Polymers are classified according to the linkages formed between the monomersPolyestersPolyamidesCondensation polymers may be:Synthetic eg. Terylene, Nylon 6.6Natural eg. Proteins, Carbohydrates such as starch and cellulose

PolyEstersMay be formed from combining diacid with dialcoholEster linkage is formedEg. Terylene (or dacron)Used to make clothing, curtains, draperies etc.

PolyAmideMay be formed from a diamine and diacids (or di-acyl chlorides)

Amide linkage is formedWater molecule is lost if di-acid is usedHCl molecule is used if di-acyl chloride is used

Eg. Nylon 6.6An early substitute for silkSimilar to polyamides in silkStronger, more durable and cheaper than natural fibresUsed for clothing, nylon ropes, parachutes etc.ProteinsMonomers are amino acidsWater molecule lost when two amino acids link to form a dipeptideMany amino acids link to form a polypeptidePolypeptides further folds up into complex networks to form the 10, 20, 30 and 40 structure of proteinsDifferent sequencing of the amino acids gives rise to different properties in proteins

CarbohydratesNaturally occurring condensation polymersExamples include:monosaccharides such as glucose and fructoseDisaccharides such as maltose and sucrosePolysaccharides such as starch and celluloseMonosaccharides are monomer units eg. glucoseDisaccharides and polysaccharides contain the ether (glycosidic) linkage The open (straight chain) form of glucose exists in equilibrium with the ring (cyclic) formCarbon 1 in glucose (sugars) is known as the anomeric carbon

Carbohydrates

MaltoseCarbohydratesStarch

CarbohydratesCellulose

CarbohydratesDifference between Starch and Cellulose

Past Paper Questions

NameMonomerPolymer (repeating unit)Uses

Poly(ethene) or polytheneEtheneCH2=CH2

Polythene has 40% of polyalkane market. Low density polythene has a low m.p. and it is used for making plastic bags and toys. High density polythene is used for kitchenware, food boxes, bowls etc

Poly(chloroethene) PVCChloroethene or vinyl chloride CH2=CHCl

PVC is more rigid than polythene. Used as a building material e.g. guttering, electrical insulation and pipes

Poly(tetrafluoroethene) TeflonTetrafluoroetheneCF2=CF2

Used for coating surfaces to reduce friction e.g. non-stick frying pans