the structure and properties of polymers
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The Structure and Properties of Polymers. Also known as Bonding + Properties. Mer – The repeating unit in a polymer chain Monomer – Polymer – Many mer - units along a chain A polymer is an organic material and the backbone of every organic material is a chain of carbon atoms. - PowerPoint PPT PresentationTRANSCRIPT
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The Structure and Properties of PolymersAlso known as
Bonding +Properties
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• Mer – The repeating unit in a polymer chain– Monomer –
• Polymer – Many mer -units along a chain
• A polymer is an organic material and the backbone of every organic material is a chain of carbon atoms.
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What is a polymer?
• A long molecule made up from lots of small molecules called
• monomers.
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• A polymer is composed of many simple molecules that are repeating structural units called monomers.
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• A single polymer molecule may consist of hundreds to a million monomers and may have a linear, branched, or network structure.
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• Covalent bonds hold the atoms in the polymer molecules together.– secondary bonds then hold groups of polymer
chains together to form the polymeric material.
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• Copolymers are polymers composed of two or more different types of monomers.
•A B
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Copolymerisation• when more than one monomer is used.
– An irregular chain structure will result eg propene/ethene/propene/propene/ethene
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• The carbon atom has four electrons in the outer shell.
• Each of these valence electrons can form a covalent bond to another carbon atom or to a foreign atom.
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• The key to the polymer structure is that two carbon atoms can have up to three common bonds and still bond with other atoms.
• The elements found most frequently in polymers are: – H, F, Cl, Bf, and I with 1 valence electron; – O and S with 2 valence electrons; – C and Si with 4 valence electrons.
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Consider the material polyethylene, which is made
from ethane gas, C2H6.
• Ethane gas has a two carbon atoms in the chain and each of the two carbon atoms share two valence electrons with the other.
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Biopolymers
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Polymer Chains (Thermoplastics and
Thermosets)
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Types of polymers• Commodity plastics• PE = Polyethylene• PS = Polystyrene• PP = Polypropylene• PVC = Poly(vinyl chloride)• PET = Poly(ethylene terephthalate)• Specialty or Engineering Plastics• Teflon (PTFE) = Poly(tetrafluoroethylene)• PC = Polycarbonate (Lexan)• Polyesters and Polyamides (Nylon)
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All the same monomer
• Monomers all same type (A) – A + A + A + A – -A-A-A-A-
• eg poly(ethene) polychloroethene PVC
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Different monomers
• Monomers of two different types A + B
• A + B + A + B• -A-B-A-B-• eg polyamides • polyesters
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Addition polymerisation
• Monomers contain C=C bonds– Double bond opens to (link) bond to next
monomer molecule• Chain forms when same basic unit is
repeated over and over.– Modern polymers also developed based on
alkynes R-C C - R’
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General form and structure of Carbon-based polymers
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Thermoplastics (80%)
• No cross links between chains.• Weak attractive forces between chains broken by
warming.• Change shape - can be remoulded.• Weak forces reform in new shape when cold.
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Thermosets
• Extensive cross-linking formed by covalent bonds.
• Bonds prevent chains moving relative to each other.
• What will the properties of this type of plastic be like?
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Longer chains make stronger polymers.
• Critical length needed before strength increases.
• Hydrocarbon polymers average of 100 repeating units necessary but only 40 for nylons.
• Tensile strength measures the forces needed to snap a polymer.
• More tangles + more touching!!!
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Crystalline polymers• Areas in polymer where chains
packed in regular way.• Both amorphous and crystalline
areas in same polymer.• Crystalline - regular chain
structure - no bulky side groups.
• More crystalline polymer - stronger and less flexible.
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Cold-drawing
• When a polymer is stretched a ‘neck’ forms.– What happens to the chains in the ‘neck’?
• Cold drawing is used to increase a polymers’ strength. – Why then do the handles of plastic carrier bags snap if you fill
them full of tins of beans?