What is a polymer???
A polymer is a molecule composed of repeating monomers which are usually connected by covalent bonds.
Branching
There are two ways of classifying a polymer by the number of branches
it has. Low-density and High-density.
Get it? It looks like a tree!
Low-Density Polyethene (LDPE)
• Polymerized at high temperatures• Significant amount of branching• Molecules are prevented from packing close together• Flexible•Melts at about 85 degrees Celsius
High-Density Polyethylene (HDPE)
• Polymerized at low temperatures• Longer chains than LDPE• Molecules are able to pack more closely together• Melts at about 120 degrees Celsius•Rigid shape
Think back to Organics…
They were classified as being either “cis” or “trans”.
“Cis” was when the molecules were on the same side.
“Trans” was when the molecules were on opposite sides.
Isotactic refers to when the alkyl groups are all on the same side ofthe polymer strand.
Think “cis”.
Plasticizers
•Small molecules that can fit between long polymer chains•Weaken attraction between chains•Polymers become more flexible•Turn from rigid to completely pliable•Example: Polyvinyl chloride
Volatile Hydrocarbons
•Add pentane during formation of polystyrene•Heated in steam, the pentane vaporizes•Expanded polystyrene is produced•Light, good thermal material•Used as packaging
Polymers can be customized by
•Strength•Thermal and electrical insulation•Flexibility•Density•Lack of reactivity
Depletion of Natural Resources
•Most polymers are carbon based•Carbon comes from oil and coal•Both sources are limited
Disposal
•Lack of reactivity makes plastics not easy to dispose•They can be burned, but if not done properly, poisonous dioxins are produced•Hydrogen Cyanide and Hydrogen Chloride
Biodegradability
•Most plastics are not natural•Are not degraded by organisms•The anaerobic conditions of landfills make biodegradation very slow or cause it to stop.
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