1. Write out the detailed mechanism for the radical chain polymerization
of styrene (vinylbenzene), designating the three stages of the
chain mechanism, and giving the repeat structure for the polymer.
What is the significance of the subscript "n" in the
repeat structure? Why is this an average value? What term
is used to describe the extent to which a polymer product contains
individual polymer molecules which have a wide or narrow range
of molecular weights?
2. Draw the dotted line/partial radical character strucutre
for the TS of a typical propagation step for this reaction and
explain, using the Method of Competing TS's (draw both competing
TS's), the preferred regiochemistry of the polymerization. What
terminology is used to describe this specific type of regiochemistry?
3. In the radical chain polymerization of ethene, the polyethylene
obtained is referred to as "low density" polyethylene
(LDPE). Explain, both in mechanistic/chemical terms, including
structural depictions, and in solid state/physical structural
terms why this polyethylene is "low density". What effect
does this have on the physical properties of the polymer?
4. Explain why the polymers obtained from the radical chain polymerization
of vinyl chloride, styrene, or acrylonitrile are unbranched.
5. Write out a rough mechanism for the Ziegler-Natta polymerization
of ethylene and explain why this polymer is termed "high
density" polyethylene (HDPE).
6. Write out a mechanism for the radical chain polymerization
of isoprene (2-methyl-1,3-butadiene). Draw the repeat structures
for both natural rubber and the polyisoprene which results from
radical polymerization.Then explain how these structures differ
and why the Ziegler-Natta catalytic system is able to polymerize
isoprene to a polymer which is identical to natural rubber.
7. Write the mechanism for the anionic polymerization of oxirane
(ethylene oxide). Use ethoxide ion as the base. Name and write
the structures of two other monomers which are readily polymerizable
by the anionic method. Name and write the structures of two monomers
which can be polymerized by the cationic method.
8.Sketch the mechanism for the thermal copolymerization of 1,6-hexanediamine
and adipic acid, showing the structure of the nylon salt obtained
upon mixing the two monomers and then the structure of the first
"dimer" and one of the two possible "trimers"
obtained upon heating. Then draw the repeat structure of Nylon
66. Why is it called "66"? What is Nylon 6 and
how is it obtained?
9.Describe the difference between chain growth and step
growth polymerizaiton. Specify one experimental test for making
10. Explain why polystyrene is soluble in organic solvents, but
the copolymer of styrene with a few percent of 1,4-divinylbenzene
is highly insoluble. What term is used to describe this kind of