Page 257 - Carrahers_Polymer_Chemistry,_Eighth_Edition

220 Carraher’s Polymer Chemistry

Macroradicals: Electron-deficient polymers having a free radical present on the chain.

Micelles: Ordered groups of soap molecules in water.
Oligoradical: Low molecular weight macroradical.
Piezoelectric: Conversion of mechanical force, such as pressure, into electrical energy.

Plasticizer: High-boiling compatible liquid that lowers T and flexibilizes the polymer.
g
Retarder: Additive that acts as a chain-transfer agent producing less active free radicals.
Saran: Trade name for copolymers of vinyl chloride and vinylidene chloride.
SBR: Rubbery copolymer of styrene and butadiene.
Suspension polymerization: Process in which liquid monomers are polymerized in liquid
droplets suspended in water.
Telogen: Additive that readily undergoes chain transfer with a macroradical.
Telomer: Low molecular weight polymer resulting form chain transfer of a macroradical with
a telogen.
Telomerization: Process in which telomers are produced by chain-transfer reactions.
Trommsdorff effect: Decrease in termination rate in viscous media that results in higher
molecular weight polymers being formed.

EXERCISES

1. Use a slanted line to show the cleavage of (a) boron trifluoride-water, (b) sodamide, and AIBN

in cationic, anionic, and free radical initiations, respectively.
2. Which type of chain-reaction polymerization is most likely to terminate by coupling?
3. If an initiator has a half-life of 4 h, what percentage of this initiator will remain after
12 hours?
4. If some heat-to-head confi guration is detected in a polymer chain know to propagate by head-
to-tail addition, what type of termination has occurred?
5. Which is the better way to increase polymer production rates: (a) increasing the temperature or
(b) increasing the initiator concentration?
6. Name three widely used thermoplastics produced by free radical chain polymerization.
7. What effect does the increase of polarity of the solvent have on free radical polymerization?
8. Show the repeat units for (a) PS, (b) PVC, and (c) PMMA.
9. Can you think of any advantage of the Trommsdorff effect?
10. What is the limiting step in free radical chain polymerization?
11. In general, which is more rapid: (a) free radical chain reactions or (b) step reaction
polymerizations?
12. If one obtained a yield of 10% polymer after 10 min of polymerizing styrene by a free-radical
mechanism, what would be the composition of the other 90%.
13. Why is t for all first-order reactions equal to 0.693/k ?

1/2 d
14. How could you follow the rate of decomposition of AIBN without directly measuring the rate
of polymerization?
15. What is the usual value for the energy of activation of free radical initiation?
16. What is the advantage of producing free radicals by UV radiation?
17. Why is PVC considered environmentally negative by some?
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18. If [M] is equal to 1 × 10 mol/L under steady-state conditions, what will [M] equal after
(a) 30, (b) 60, and (c) 90 min?
19. In general, what is the activation energy in free radical chain propagation of polymer chains?
20. What is the relationship between the rate of propagation and the concentration of
initiators [I]?
21. When chain transfer with solvent occurs, what effect does this have on the average degree of
polymerization?
22. In the free radical polymerization name two steady-state assumptions.

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