Chemistry Reference
In-Depth Information
3-14
Solution viscosities for a particular polymer and solvent are plotted in the
form (
η 2 η
0
)/(
c
η
0
) against
c
where
η
is the viscosity of a solution of poly-
mer with concentration
c
gcm
2
3
and
η
0
is the solvent viscosity. The plot
is a straight line with an intercept of 1.50 cm
3
g
2
1
and a slope of
0.9 cm
6
g
2
2
. Give the magnitude and units of Huggins's constant for this
polymer
solvent pair.
3-15 The following average molecular weights were measured by gel perme-
ation chromatography of a poly(methyl methacrylate) sample:
10
5
10
5
10
5
M
n
2
:
15
3
;
M
v
4
:
64
3
;
M
w
4
:
97
3
10
5
10
6
10
6
M
z
9
:
3
;
M
z
1
1
1
:
3
;
M
z
1
2
2
:
3
39
55
22
Provide quantitative estimates of the breadth and skewness of the
weight distribution of molecular weights.
3-16 Einstein's equation for the viscosity of a dilute suspension of spherical
particles is
η=η
0
5
1
1
2
:
5
φ
(3-61)
where
is the volume fraction of suspended material. Express the intrinsic
viscosity (in deciliters per gram) as a function of the apparent specific vol-
ume (reciprocal density) of the solute.
φ
3-17 This multipart question illustrates material balance calculations used, for
example, in formulating polyurethanes. Refer to Section 1.5.4 for some of
the reactions of isocyanate groups. This problem is an extension of the
concepts mentioned in
Section 3.1.9
on end-group determinations. Some
useful definitions follow:
Equivalent weight,
E5
weight of compound per active group for a
given reaction. (total weight)/(equivalent weight)
5
no. of equivalents.
M
n
f
E
5
(3-17-i)
where
f
is the functionality, i.e., the number of chemically effective groups
per molecule for the reaction of interest (
Section 1.3.2
). In hydroxyl-
terminated polymers, which are often called polyols,
E
follows from the
definition of the term hydroxyl number, OH, in
Section 3.1.9
, as: Then
56
:
1
ð
1000
Þ
E5
(3-17-ii)
OH
Then:
56
:
1
ð
1000
Þ
f
M
n
5
5
Ef
(3-17-iii)
OH
