Page 708 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Solutions 671

27. (a). The amide is a stiffening group.
28. Because of the presence of bulky pendant groups.
29. Bakelite is a thermal set material and not moldable once it is formed. Thus prepolymer is used
to make molded products.
30. Not particularly, since the polyamine reacts producing a polyurea. However, other propellants
are used commercially in foam production.
31. Use an excess of the glycol.
32. DP = 1/1 − p.
n
33. DP steadily increases.
34. Because of the presence of strong polar groups.
35. The precursor, furfural, is produced from waste corn cobs.
36. Some group that can be cross-linked generally a carbon–carbon double bond.
37. No: resorcinol is trifunctional and very reactive.
38. Phenolic resins were developed before there was much information on polymer science. Those
involved in an art have a tendency to create new terms to describe what they have observed.
39. Most people prefer to use light-colored dinnerware.
40. All three.
41. (a). (b) would be a branched chain.
42. Microfibers have an extremely small diameter that allows a fabric to be woven that is light

weight and strong. Microfibers can be tightly woven so that wind, rain, and cold do not eas-

ily penetrate but allow perspiration to pass through them. Microfibers are also very fl exible

because the small fibers can easily slide back and forth on one another.
43. Polyurethanes are mainly employed as foam and elastomer materials.
44. Open-celled foams allow air to readily pass through them, allowing the material to be more
flexible. Closed-celled foams retain the air trapped within them, resulting in retention of heat/

cold so they are good insulators.
45. LCs are composed of materials that reorient themselves on application of heat, pressure, or
some other external change.
46. LCs are used in watches, computer screens, and in TV screens.
47. PEGs are water soluble and impart water solubility when attached to otherwise water-insoluble
drugs. Further, PEG is generally biologically benign.
48. Aramides is the name given to polyamides or nylons that have aromatic groups, generally phe-
nylenes, in their backbone.
49. Stiff, strong, and high melting.

CHAPTER 5
1. (a) A small amount of reactants, dimer, trimer, and oligomers, plus low molecular weight poly-
mers, (b) high molecular weight polyisobutylene plus monomer.
2. A Lewis base–cocatalyst complex. Actually, the proton is the initiator here.
3. A carbonium ion.
4. A macrocarbonium ion.
5. A gegenion.
6. (a).
7. (b).
8. The macroions have similar charges.
9. (a).
10. (b).
11. (a) HDPE or PP, (b) IR, EP, or butyl rubber (IIR), and (c) PP.
12. (a).

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