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A polymer is a high molar mass molecular compound made up of many repeating chemical units.
Naturally occurring polymers• Proteins• Nucleic acids• Cellulose• Rubber
Synthetic polymers• Nylon• Dacron• Lucite
A polymer is a large molecule made by linking togetherrepeating units of small molecules called monomers
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Characterizing a Polymer
• Structure • Classification • Synthesis
Structure of a Polymer
• Skeletal Structure • Chemical Structure
Skeletal Structure• Linear – a chain with two ends
Skeletal Structure• Branched – have side chains
Skeletal Structure• Crosslinked (Networked) – chains are
connected to other chains
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The simple repeating unit of a polymer is the monomer.
Homopolymer is a polymer made up of only one type of monomer
( CF2 CF2 )n
Teflon
( CH2 CH2 )n
Polyethylene
( CH2 CH )n
Cl
PVC
25.2
Copolymer is a polymer made up of two or more monomers
Styrene-butadiene rubber
( CH CH2 CH2 CH CH CH2 )n
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Classifications
• Thermoplastic• Elastomer• Thermoset
Thermoplastics
• Linear or branched polymers which can be melted when heat is applied.
• Can be molded into any shape with processing techniques such as injection molding or extrusion.
• Most common “plastics”
Thermoplastics
• Plastics – bottles, grocery bags, water piping, rope, fishing line, car parts
• Most are recyclable • Natural thermoplastics – silk,
cellulose (proteins), polylactic acid
Codes for Plastics
• 1 – PETE – soft drink bottles• 2 – LDPE – plastic bags, toys• 3 – PVC – water pipes• 4 – HDPE – milk jugs • 5 – PP – bottle caps• 6 – PS – styrofoam
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Elastomers• Crosslinked (networked) rubbery
polymers that can be stretched easily (3-10x original size)
• Rapidly recover original dimensions when applied stress is released.
• Low degree of crosslinking
Elastomers
• Uses – examination gloves, rubber bands, bouncing balls
• Not recyclable –Degrades (burns/scorches) when
heat is added• Natural elastomers – natural rubber,
latex
Thermosets• Normally are rigid materials. • Network polymers in which chain
motion is greatly restricted by a high degree of crosslinking.
• Cannot be reshaped once formed.
epoxy
Thermosets
• Uses – high temperature electrical applications, super glue, counter top laminates, epoxy resins, tires (vulcanized rubber)
• Cannot be recycled (burn/scorch with heat)
• Natural* thermosets – vulcanized rubber
PolymerizationAddition PolymerizationCondensation Polymerization
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Polyaddition
• Reactions in which monomers combine without the elimination of a small molecule. – Usually involves the breaking of a double
bond.
Polyaddition with Radicals
• Initiation – Creation of an active site (free radical).
• Propagation – Growth of polymer chain by addition of a monomer to an active site and the creation of a new active site.
Polyaddition with Radicals
• Termination – Growth of chain stops. – Combination – Two growing chains collide.– Disproportionation – A hydrogen atom is
added to the end of a growing chain.
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Occurs in the presence of a Lewis acid
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Polycondensation
• Reactions in which small molecules (H2O, HCl) are eliminated when the monomers combine. e.g. Nylon66
CH2
CC
O
OH
O
OH
4+
NH2
NH2
NH
NH2
CH2 CC
O
OH
O
4
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Properties and uses• Good fibre-forming material and is converted into
commercial fibres.• Such fibres have high stretch resistance, high crease and
wrinkle resistance.• Highly resistant to mineral and organic acid, but is less
resistant to alkalies.• Used for making synthetic fibres like terylene, dacron etc.• For blending with wool to provise better crease and wrinkle
resistance.• A glass reinforcing material in safety helmets, aircraft battery
boxes, etc.
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