Chemistry Reference
In-Depth Information
MAN
ð
M
1
Þ=
S:
r
1
5
0
:
44
;
r
2
5
0
:
37
MAN
ð
M
1
Þ=
AMS:
r
1
5
0
:
38
;
r
2
5
0
:
53
S
ð
M
1
Þ=
AMS:
r
1
5
1
:
124
;
r
2
5
0
:
627
9-3
When 0.3mol fraction methacrylonitrile is copolymerized with styrene in a
radical reaction, what is the average length of sequences of each monomer
in the copolymer?
9-4
Rank the following monomers in order of their increased tendency to alter-
nate in copolymerization with butadiene and explain your reasoning: vinyl
acetate, styrene, acrylonitrile, and methyl methacrylate. (
Hint:
Use
Q
e
values if reactivity ratios are not readily available.)
9-5
(a) Acrylonitrile (monomer 1,
r
1
5
0.9) is copolymerized with 0.25 mol
fraction vinylidene chloride (monomer 2,
r
2
5
0.4). What fraction of
the acrylonitrile sequences contain 3 or more acrylonitrile units?
(Polyacrylonitrile is used to make “acrylic” fibers. Copolymerization
with vinylidene chloride reduces the flammability of such products.
Such copolymers form the basis of “mod-acrylic” fibers.)
(b) What is the feed composition for copolymerization of vinylidene chlo-
ride and acrylonitrile such that the copolymer composition does not
vary with the conversion of monomers to polymer?
9-6
The extent of reaction at which gelation occurs in the copolymerization of
a vinyl monomer and a divinyl monomer can be increased by increasing
the concentration of free-radical initiator, at fixed polymerization tempera-
ture and comonomer feed composition. Explain why this should be so.
9-7
A thermosetting appliance enamel consists of a terpolymer comprising
about 72 parts of vinyl toluene (70/40 meta/para) with about 20 parts of
ethyl acrylate (to reduce brittleness of the copolymer) and 8 parts of an
acidic vinyl comonomer. The acid is incorporated in the copolymer to pro-
vide sites for subsequent cross-linking with a diepoxide. It seems reason-
able to expect that grease and stain resistance of the cross-linked enamel
will be enhanced if the cross-links are not clustered and almost all initial
polymer molecules contain at least one or a few cross-linking sites. To
achieve this in a batch copolymerization, what are the best reactivity ratios
(approximately) of the major component (vinyl toluene) and the vinyl acid
comonomer? Show your reasoning.
9-8
It has been suggested that free-radical polymerization would be a useful
way to react an equimolar mixture of allyl acetate and methyl methacry-
late. Is this a good idea? (Allyl acetate:
e
52
1.07,
Q
5
0.24; methyl meth-
acrylate:
e
5
0.40,
Q
5
0.78).
9-9
The copolymerization of ethylene and propylene is found to be essentially
random (
r
1
r
2
D
1) with (C
2
H
5
)
2
AlCl/VO(OC
2
H
5
)
3
catalyst in chloroben-
zene at 30
C. (Such polymerizations are discussed in Chapter 11.) The
