Callister - An introduction - 8th edition

566 • Chapter 14 / Polymer Structures
average molecular weight and (b) the weightaverage
molecular weight. (c) If it is known
that this material’s degree of polymerization
is 710, which one of the polymers listed in
Table 14.3 is this polymer? Why?
Molecular Weight
Range (g/mol) x i w i
15,000–30,000 0.04 0.01
30,000–45,000 0.07 0.04
45,000–60,000 0.16 0.11
60,000–75,000 0.26 0.24
75,000–90,000 0.24 0.27
90,000–105,000 0.12 0.16
105,000–120,000 0.08 0.12
120,000–135,000 0.03 0.05
14.7 Is it possible to have a poly(methyl methacrylate)
homopolymer with the following molecular
weight data and a degree of polymerization
of 527? Why or why not?
Molecular Weight
Range (g/mol) w i x i
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
14.8 High-density polyethylene may be chlorinated
by inducing the random substitution of
chlorine atoms for hydrogen.
(a) Determine the concentration of Cl (in
wt%) that must be added if this substitution
occurs for 5% of all the original hydrogen
atoms.
(b) In what ways does this chlorinated polyethylene
differ from poly(vinyl chloride)?
Molecular Shape
14.9 For a linear freely rotating polymer molecule,
the total extended chain length L depends
on the bond length between chain atoms d,
the total number of bonds in the molecule N,
and the angle between adjacent backbone
chain atoms u, as follows:
L Nd sin a u 2 b
(14.11)
Furthermore, the average end-to-end distance
r for a randomly winding polymer molecule
in Figure 14.6 is equal to
(14.12)
A linear polytetrafluoroethylene has a numberaverage
molecular weight of 500,000 g/mol;
compute average values of L and r for this
material.
14.10 Using the definitions for total chain molecule
length L (Equation 14.11) and average
chain end-to-end distance r (Equation 14.12),
for a linear polyethylene determine the
following:
(a) the number-average molecular weight
for L 2500 nm
(b) the number-average molecular weight
for r 20 nm
Molecular Configurations
14.11 Sketch portions of a linear polystyrene molecule
that are (a) syndiotactic, (b) atactic,
and (c) isotactic. Use two-dimensional
schematics per footnote 8 of this chapter.
14.12 Sketch cis and trans structures for (a) butadiene,
and (b) chloroprene. Use twodimensional
schematics per footnote 11 of
this chapter.
Thermoplastic and Thermosetting Polymers
14.13 Make comparisons of thermoplastic and thermosetting
polymers (a) on the basis of mechanical
characteristics upon heating and
(b) according to possible molecular structures.
14.14 (a) Is it possible to grind up and reuse
phenol-formaldehyde? Why or why not?
(b) Is it possible to grind up and reuse
polypropylene? Why or why not?
Copolymers
14.15 Sketch the repeat structure for each of the following
alternating copolymers: (a) poly (butadiene-chloroprene),
(b) poly(styrene-methyl
methacrylate), and (c) poly(acrylonitrilevinyl
chloride).
14.16 The number-average molecular weight of a
poly(styrene-butadiene) alternating copolymer
is 1,350,000 g/mol; determine the averr
d2N