C8 Condensation+Polymer com

8/9/2019 C8 Condensation+Polymer com

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Condensation polymersC.8.1 Distinguish between addition and condensation polymers in terms of their

structures.C.8.2 Describe how condensation polymers are formed from their monomers.

C.8.3 Describe and explain how the properties of polymers depend on their structural features.

C.8.4 Describe ways of modifying the properties of polymers.C.8.5 Discuss the advantages and disadvantages of polymer use.


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Distinguish between addition

polymer and condensation polymer Addition polymer formed by an addition

reaction, where manymonomers bondtogether viarearrangement of bonds without the lossof any atom or molecule.

Usually made fromalkenes

Condensation polymer formed by a

condensation reactionwhere a molecule,usually water, is lostduring the formation

Made from monomersthat contain at least

two reactive functionalgroups( or samefunctional group atleast twice)


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F ormation of polyester

Polyethen terephthalate (PET)When benzene-1,4-dicarboxylic acid andethane-1,2 diol reacts


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Phenol-methanal plasticThe reaction is a condensationpolymerisation in which water iseliminated as a hydrogen atomfrom the benzene ring of each of two neighbouring phenolmolecules combines with the

oxygen atom from a methanalmolecule ( When acid or alkali isadded to the mixture of phenoland methanal)The remaining CH2 group fromthe methanal molecule then formsa bridge between twoneighbouring phenol molecules.This process, repeated manythousands of times, forms chainsof phenol and methanal moleculeslinked in this way.


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Mechanism

When acid or alkali isadded to the mixtureof phenol and

methanol. Methanal issubstituted in the 2- or 4- position in thephenol

It then undergoes acondensation reactionwith another phenolmolecule.


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L ong Chain

L ong chain of phenol-methanal plastics(covalent cross linking three dimensionalstructure) is built up when further polymerizationtakes place


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F ormation of Polyurethane

When polyhydric alcohols (e.g. diols or triols) reactswith compounds containing more than oneisocyanate functional group, -NCO will producepolyurethanes.


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PolyurethanePolyurethanes are somehow considered asaddition polymers since there is no smallmolecules formed during the reaction. However there is no urethane monomers that addtogether to form polyurethanes.

Polyurethanes are made in situ and mouldedinto shape wanted.

(In the reaction mixture." There are numerousunstable molecules which must be synthesizedin situ (i.e. in the reaction mixture but cannot beisolated on their own )


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Properties of polymers

Properties of condensation polymers depend ontheir structures.The benzene ring bonds in more than oneposition of phenol-methanal plastics forms 3-Dcross-linked structure


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Properties

The structure gives high strength.Therefore the compound is High melting point ( decompose before

melting) Unreactive High electrical resistance

It can be use as an ingredient in worktopsand printed-circuit-board insulationBefore it was use as the casing for radios


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K evlar

K evlar is a polyamideIt forms when 1,2-diaminobenzene(paraphenylenediamine) condenses withbenzene-1,4-dicarbonyl chloride(terephthaloyldichloride)


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L ong chain

F urther polymerization forms a strong three-dimensional structure because of the hydrogenbonding between the long rigid chainK evlar is used to produce lightweight bullet-proof vest, composites for motor-cycle helmetsand amour.


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Modification of polymers

Apart from adding plasticizers (covered inaddition polymer) there are 3 more waysto modify polymers Blowing air into polyurethane to make

polyurethane foams ( cushions and thermalinsulator)

Blending fibres of polyesters (PET) with other manufactured or natural fibres to makeclothes become dye-fast and comfortablethan pure polyesters.


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Modifying polymer

Another way is adding chemicals ( this processis called doping polymer) such as Iodine which removes electrons

or Alkali metals which adds electrons

When ethyen is polymerized, the cis-form of polyethene is a electrical conductor due to thedeloclization of the pi electrons.

The conductivity is increaseddramatically after doping I 2


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AdvantagesUse to produce lightweight bullet-proof vest, composites for motor-cycle helmets and amour. (PET)Devices such as billiard balls, dominoes, Mahjongg tiles and other gaming tilesets, and movers/pieces for games like chess, checkers,and backgammon, are constructed of Bakelite(phenol-methanal

plastics) for the look, durability, fine polish, weight, and sound of theresulting piecesPolyurethane products have many uses. Over three quarters of theglobal consumption of polyurethane products is in the form of foams,with flexible and rigid types being roughly equal in market size. Inboth cases, the foam is usually behind other materials: flexiblefoams are behind upholstery fabrics in commercial and domesticfurniture; rigid foams are inside the metal and plastic walls of mostrefrigerators and freezers, or behind paper, metals and other surfacematerials in the case of thermal insulation panels in the constructionsector.


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Disadvantages

The disadvantages of condensationpolymer are similar to addition polymer

L

ow-reactivity Not easy to dispose off. Generally not biodegradable

Produce hydrogen cyanide gas whenpolyurethanes are burned.

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