1.  CHEMICALLY IDENTICAL
Paraffin wax candle
Body armor
Plastic milk jug
Fishing line
 CHEMICALLY IDENTICAL
Polymer Science allows
us to engineer these
materials and distinguish
them from one another!

2. Polymers in Brief
A polymer is a large (macro) molecule with a specific repeating structure
Polymer properties are dictated by
The bonding within the chains
The bonding between the chains
The size of the chains
The shape of the chains
The structure of a polymer is denoted using the smallest repeating unit:
X Y Z n
…-X-Y-Z-X-Y-Z-X-Y-Z-X-Y-Z-X-Y-Z-X-Y-Z-…

3. Common Polymers Poly(Ethylene Terephthalate Ester)
High Density PolyEthylene
Poly(Vinyl Chloride)
Low Density PolyEthylene
PolyPropylene
PolyStyrene
Poly(Methyl MethAcrylate) (Plexiglas),
PolyCarbonate (Lexan), PolyUrethanes,
PolyTetraFluoroEthylene (Teflon),
PolyAmides (Nylon, Kevlar, Nomex), PolyImides, other Polyesters, etc.

4. All-Racemic = syndiotactic
All-Meso = isotactic
All-Racemic = syndiotactic
Random = atactic
Stereoisomerism (in vinyl polymers)
Example 1.
Diads in Poly(vinyl chloride)
Example 2. Stereoregularity in polypropylene

5. Stereoisomerism (in polypropylene)
 WHY THIS MATTERS
Isotactic polypropylene
Tm = °C
Strong, hard material with good resistance to stress, cracks, and chemical reaction
Syndiotactic polypropylene
Tm = °C
Softer than isotactic polypropylene
Tough, clear, and stable when exposed to gamma radiation
Atactic polypropylene
Tm < 0 °C
Soft, rubbery polymer

6. Structural isomerism (in polydienes)
Diene numbering scheme
Natural rubber
WHY THIS
MATTERS:
1,2 and 3,4
units are
more reactive
to crosslinking
(vulcanization)
than 1,4 units
Example: Structural isomers of poly(isoprene)

7. The Effects of Molecular Weight
Gases / fuels
Solvents / fuels / oils
Paraffin waxes
Low-MW polyethylene
High-MW polyethylene