16-11-2012, 05:17 PM
Polymer Chemistry
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Definitions
Polymer – A very long molecule composed of repeating units connected by covalent bonds
Monomer – A repeated unit in a polymer. The reactant for the polymerization reaction.
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”
Plastics – bottles, grocery bags, water piping, rope, fishing line, car parts
Most are recyclable
Natural thermoplastics – silk, cellulose (proteins), polylactic acid
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
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
Polycondensation
Reactions in which small molecules (H2O, HCl) are eliminated when the monomers combine.
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.
[attachment=39858]
Definitions
Polymer – A very long molecule composed of repeating units connected by covalent bonds
Monomer – A repeated unit in a polymer. The reactant for the polymerization reaction.
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”
Plastics – bottles, grocery bags, water piping, rope, fishing line, car parts
Most are recyclable
Natural thermoplastics – silk, cellulose (proteins), polylactic acid
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
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
Polycondensation
Reactions in which small molecules (H2O, HCl) are eliminated when the monomers combine.
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.