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Polymer Chemistry. The Basic Concepts - Himenz P.C.

Himenz P.C. Polymer Chemistry. The Basic Concepts - Copyright, 1984. - 736 p.
Download (direct link): polymerchemistry1984.djvu
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that are especially pertinent to the study of polymers. The discussion of
this topic brings together certain basic ideas from electromagnetism,
optics, and solution thermodynamics. Even though it is explicitly through
an expression for osmotic pressure that the molecular weight enters the
light-scattering equations, these two techniques give different averages
for M. This makes these two methods complementary rather than redundant,
and, in combination, they provide information concerning the width of the
molecular weight distribution.
Although the emphasis in these last chapters is certainly on the
polymeric solute, the experimental methods described herein also measure
the interactions of these solutes with various solvents. Such
interactions include the hydration of proteins at one extreme and the
exclusion of poor solvents from random coils at the other. In between,
good solvents are imbibed into the polymer domain to various degrees to
expand coil dimensions. Such quantities as the Flory-Huggins interaction
parameter, the 0 temperature, and the coil expansion factor are among the
ways such interactions are quantified in the following chapters.
Problems
1. Write structural formulas for maleic anhydride (ML) and stilbene
(M2). Neither of these monomers homopolymerize to any significant extent,
presumably owing to steric effects. These monomers form a copolymer,
Problems
497
however, with ri = r2 = 0.03.f Criticize or defend the following
proposition: The strong tendency toward alternation in this copolymer
suggests that polarity effects offset the steric hindrance and permit
copolymerization of these monomers.
2. Styrene and methyl methacylate have been used as comonomers in many
investigations of copolymerization. Use the following list $ of r! values
for each of these copolymerizing with the monomers listed below to rank
the latter with respect to reactivity:
M2 Styrene as Methyl methacrylate
as
Acrylonitrile 0.41 1.35
Allyl acetate 90 23
1,2-Dichloropropene-2 5 5.5
Methacrylonitrile 0.30 0.67
Vinyl chloride 17 12.5
Vinylidene chloride 1.85 2.53
2-Vinyl pyridine 0.55 0.395
To the extent that the data allow, suggest where these substituents might
be positioned in Table 7.3.
The following reactivity ratios describe the polymerization of
acrylonitrile
(Mi) with the monomers listed:
M2 ri 4
Butadiene 0.02 0.3
Methyl methacrylate 0.15 1.22
Styrene 0.04 0.40
Vinyl acetate 4.2 0.05
Vinyl chloride 2.7 0.04
Use the Q and e values listed in Table 7.4 for each of the
comonomers to give five independent estimates of Q and e for
acrylonitrile. Compare the average of these four with the values given
for acrylonitrile in Table 7.4.
t F. M. Lewis and F. R. Mayo, J. Am. Chem. Soc. 70:1533 (1948). tRef. 4.
Ref. 4.
498
Polymers with Microstructure
4. As part of the research described in Fig. 7.5, Winston and
Wichacheewaf measured the percentages of carbon and chlorine in
copolymers of styrene (molecule 1) and 1-chloro-l,3-butadiene (molecule
2) prepared from various feedstocks. A portion of their data is given
below:
fl Percent Percent Cl
0.892 81.80 10.88
0.649 71.34 20.14
0.324 64.95 27.92
0.153 58.69 34.79
Use these data to calculate Fls the mole fraction of styrene in
these copolymers.
5. Additional data from the research of the last problem J yield the
following pairs of flf Fi values (remember that styrene is component 1 in
the styrene-1-chloro-1,3-butadiene system):
fi Fi fi Fi
0.947 0.829 0.448 0.362
0.861 0.688 0.247 0.207
0.698 0.515 0.221 0.200
0.602 0.452
Use the form suggested by Eq. (7.54) to prepare a graph based on
these data and evaluate r! and r2.
6. The reactivity ratios for the styrene (M^-l-chloro-l,3-butadiene (M2)
system were found to be r! = 0.26 and r2 = 1.02 by the authors of the
research described in the last two problems using the results of all
their measurements. Use these r values and the feed compositions listed
below to calculate the fraction expected in the copolymer of 1-
chlorobutadiene sequences of lengths v = 2, 3, or 4. From these
calculated results, evaluate the ratios N222 /N22 and N2222 /N222.
Copolymers prepared from these feedstocks were dehydrohalogenated to
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