CHAPTER 14
POLYMER STRUCTURES
PROBLEM SOLUTIONS
14.4
We are asked to compute the number-average degree of polymerization for polypropylene, given
that the number-average molecular weight is 1,000,000 g/mol.
The mer molecular weight of
polypropylene is just
m = 3(A
C
) + 6(A
H
)
= (3)(12.01 g/mol) + (6)(1.008 g/mol) = 42.08 g/mol
If we let
n
n
represent the number-average degree of polymerization, then from Equation (14.4a)
n
n
=
M
n
m
=
10
6
g/mol
42.08 g/mol
= 23,700
14.7
(a)
From the tabulated data, we are asked to compute
M
n
, the number-average molecular weight.
This is carried out below.
Molecular wt.
Range
Mean M
i
x
i
x
i
M
i
8,000-20,000
14,000
0.05
700
20,000-32,000
26,000
0.15
3900
32,000-44,000
38,000
0.21
7980
44,000-56,000
50,000
0.28
14,000
56,000-68,000
62,000
0.18
11,160
68,000-80,000
74,000
0.10
7400
80,000-92,000
86,000
0.03
2580
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