Page 710 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Solutions 673

49. Increased crystallinity, higher T , less permeable, higher stress–strain ratio.
g
50. CH 3
CH 3
R
R R

R
(a) Cis (b) Trans

51. CH 3
CH 3
R
R
R
R
CH 2
(a) (b)

52. A chromia catalyst supported on silica (Phillips catalyst).
53. cis-Polyisoprene.
54. Ethylene–propylene copolymer.
55. Entrenchment of catalysts that must be removed; often broad molecular weight distribution;
and, in comparison with soluble stereoregulating catalysts, not as exacting control of tacticity
of resulting products.
56. Soluble steroregulating catalysts overcome the problems by having a greater control of the
tacticity of the resulting polymers; little or no entrapment of catalysts; and narrower molecular
weight distributions.
57. Overall cost including shipping; how strong the bags need to be as well as their ability to withstand
punctures; ability to withstand natural elements of water, fertilizer, sunlight, and heat/cold.
58. Mixing the HDPE when melted and rapidly cooling, locking in some amorphous character.
59. Many properties are drastically different depending on the particular form of the material. The
one material with the lower elongation may be largely crystalline whereas the material with the
high elongation may be an amorphous form. This points out the need that must be taken when
comparing values from different tables.
60. Yes. Butadiene polymers typically have C=C within them that can be exploited to form
cross-links.
61. While PE is a simple structure, the variations in structure offer a wide range of properties and
application opportunities. Also, the ethylene monomer is readily available on a large scale and
it is inexpensive.

CHAPTER 6
1. (a) H/:BF OH; (b) Na/:NH ; and (c) (H C) –C(CN)–N/N–C(CN)–(CH )
2
2
3
3
3 2
2. Free radical chain polymerization.
3. 12.5%.
4. Coupling.
5. Neither since both will reduce the average DP.
6. LDPE, PVC, PS, and so on.
7. None, provided the system is a homogeneous solution.

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K10478.indb 673
K10478.indb 673 9/14/2010 3:44:15 PM