Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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Questions and Problems • 125

Rosen, S. L.,Fundamental Principles of Polymeric

Materials, 2nd edition, Wiley, New York, 1993.

Rudin, A.,The Elements of Polymer Science and

Engineering, 2nd edition, Academic Press, San

Diego, 1999.

Sperling, L. H.,Introduction to Physical Polymer

Science, 4th edition, Wiley, Hoboken, NJ, 2006.

Young, R. J. and P. Lovell,Introduction to Polymers,

2nd edition, Chapman and Hall, New York,

1991.

QUESTIONS AND PROBLEMS

Additional problems and questions for this chapter may be found on both Student and

Instructor Companion Sites atwww.wiley.com/college/callister.

Molecular Weight

4.1Compute repeat unit molecular weights for(a)

polytetrafluoroethylene and(b)nylon 6,6.

4.2 (a)Compute the repeat unit molecular weight

of polypropylene.

(b)Compute the number-average molecular

weight for a polypropylene for which the

degree of polymerization is 15,000.

4.3Below, molecular weight data for a poly-

tetrafluoroethylene material are tabulated.

Compute (a) the number-average molecu-

lar weight,(b)the weight-average molecular

weight, and(c)the degree of polymerization.

Molecular Weight

Range(g/mol) xi wi

10,000–20,000 0.03 0.01

20,000–30,000 0.09 0.04

30,000–40,000 0.15 0.11

40,000–50,000 0.25 0.23

50,000–60,000 0.22 0.24

60,000–70,000 0.14 0.18

70,000–80,000 0.08 0.12

80,000–90,000 0.04 0.07

4.4Is it possible to have a poly(vinyl chloride)

homopolymer with the following molecular

weight data, and a degree of polymerization

of 1120? Why or why not?

Molecular Weight

Range(g/mol) wi xi

8,000–20,000 0.02 0.05

20,000–32,000 0.08 0.15

32,000–44,000 0.17 0.21

44,000–56,000 0.29 0.28

56,000–68,000 0.23 0.18

68,000–80,000 0.16 0.10

80,000–92,000 0.05 0.03

Molecular Shape

4.5For a linear polymer molecule, the total chain

lengthLdepends on the bond length between

chain atomsd, the total number of bonds in the

moleculeN, and the angle between adjacent

backbone chain atomsθ, as follows:

L=Ndsin

(

θ

2

)

(4.9)

Furthermore, the average end-to-end distance

for a series of polymer moleculesrin Figure

4.6 is equal to

r=d

√

N (4.10)

A linear polyethylene has a number-average

molecular weight of 300,000 g/mol; compute

average values ofLandrfor this material.

Molecular Configurations

4.6Sketch portions of a linear polypropylene

molecule that are(a)syndiotactic,(b)atac-

tic, and (c) isotactic. Use two-dimensional

schematics per footnote 8 of this chapter.

Thermoplastic and Thermosetting Polymers

4.7Make comparisons of thermoplastic and ther-

mosetting polymers(a)on the basis of me-

chanical characteristics upon heating, and(b)

according to possible molecular structures.

Copolymers

4.8The number-average molecular weight of

a poly(acrylonitrile-butadiene) alternating

copolymer is 1,000,000 g/mol; determine the

average number of acrylonitrile and butadi-

ene repeat units per molecule.

4.9An alternating copolymer is known to have a

number-average molecular weight of 100,000

g/mol and a degree of polymerization of 2210.