The phenol formaldehyde rxn

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The phenol formaldehyde rxn
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Bakelite
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Bakelite - Material of a Thousand Uses
Bakelite telephone
Clear Bakelite items
Phenolic resin/celluloid clock
Bakelite microphone
Bakelite radio
Bakelite camera
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Crosslinking
Take linear polymer chains link using covalent
bonds
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Crosslinking
Ex rxn of natural rubber or poly(isoprene)
with sulfur - interconnects the chains by
reacting with the double bonds (vulcanization)
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Crosslinking
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3 types isotactic syndiotactic atactic
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isotactic
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Polypropylene - largely isotactic isotactic
character of PP allows "crystallization" as a
result, material can be stiffer
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Polystyrene - atactic Polypropylene -
largely isotactic PVC -
largely atactic
(some syndiotactic sequences) PMMA
-atactic
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miscible immiscible
single phase phase separated
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increasing
molecular weight
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Chains have different molecular weights There is
a distribution
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Is it important?
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Is it important?
Very important in processing If viscosity too
high, polymer difficult to process
If too low, an extruded material won't hold
together until it solidifies
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Step 1 make preform by extrusion or injection
molding
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Step 1 make preform by extrusion or injection
molding
Step 2 use air pressure to inflate preform
inside closed, hollow mold. Polymer expands to
take shape of cooled mold solidifies under
pressure
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• Normal crystalline materials
• Either crystalline (100 , neglecting defects )
  or amorphous at a particular temperature
• Melt at a sharp, well-defined temperature

• Crystallizable polymers
• Never 100 crystalline
• Melt over a range of temperatures

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