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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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preparative column, the solvent was evaporated away, and the weight of
each polymer fraction was obtained. The molecular weights of each
fraction were obtained using an analytical gel permeation chromatograph
calibrated in terms of both Mn and Mw. The following data were obtained
t:
t H. Lutje and G. Meyerhoff, Makromol. Chem. 68:180 (1963).
$Y. Kato, T. Kametani, K. Furukawa, and T. Hashimoto, J. Polym. Sci.
Polym. Phys. Ed. 13:1695 (1975).
Problems
657
Fraction Mass polymer Mn X 10"4 Mw X 10"4
number (mg) (g mol-1) (g mol-1)
6 2 109 111
7 8 90.8 92.5
8 20 76.7 78.0
9 42 62.3 63.5
10 64 51.5 52.5
11 84 41.7 42.5
12 102 34.7 35.4
13 110 28.7 29.3
14 110 23.3 23.8
15 96 18.9 19.4
16 86 15.9 16.3
17 68 13.0 13.3
18 54 1 1.0 11.2
19 42 9.14 9.35
20 30 7.52 7.68
21 28 6.16 6.28
22 18 5.12 5.22
23 12 4.09 4.18
24 8 3.33 3.40
25 6 2.63 2.69
26 5 2.01 2.06
27 4 1.52 1.56
28 3 1.13 1.16
29 2 0.83 0.85
30 1 0.59 0.61
Calculate Mn and Mw and the ratio Mw/Mn for the original polymer.
Also evaluate the ratio Mw/Mn for the individual fractions. Comment on
the significance of Mw/Mn for both the fractionated and unfractionated
polymer.
12. Use the model for the size exclusion of a spherical solute molecule
in a cylindrical capillary to calculate KGPC for a selection of R/a
values which are compatible with Fig. 9.16. Plot your values on a
photocopy or tracing of Fig. 9.16. On the basis of the comparison between
these calculated points and the line in Fig. 9.16 drawn on the basis of a
statistical consideration of chain exclusion, criticize or defend the
following proposition: There is not much difference between the values
calculated by the equivalent sphere and statistical models. The
discrepancy between various experimental methods for evaluating a is much
greater than the differences arising from different models. Even for
random coil molecules the simple equivalent sphere model is acceptable
for qualitative discussions of VR.
658
Frictional Properties of Polymers in Solution
13. Three polystyrene samples of narrow molecular weight distribution
were investigated! for their retention in GPC columns in which the
average particle size of the packing was varied. In all instances the
peaks were well resolved. The following results were obtained:
Mean dimension of particles Molecular weight of
in packing () polystyrene
411,000 51,000 2,030
120 tR (min) 160 200 230
VR (ml) 160 200 230
44 tR (min) 9 12 15
VR (ml) 4.5 6.0 7.5
6 tR (sec) 20 2.7 32
VR (ml) 0.33 0.43 0.53
It is also known that smaller particles in the packing material are
more difficult to pack homogeneously, and that higher pressures are
required to pump liquid through them. On the basis of these observations,
criticize or defend the following proposition: Between the largest and
smallest particle sizes in these packing materials there is a 7.5-fold
decrease in retention time. This increase in rate with undiminished
resolution shows that still smaller packing particles should be
developed, perhaps using something like emulsion polymerization to
prepare small, cross-linked polymer gels.
Bibliography
1. Flory, P. J., Principles of Polymer Chemistry, Cornell University
Press, Ithaca, N.Y., 1953.
2. Hiemenz, P. C., Principles of Colloid and Surface Chemistry, Marcel
Dekker, New York, 1977.
3. Lauffer, M. A.,/. Chem. Educ. 58:250 (1981).
4. Richards, E. G., An Introduction to the Physical Properties of Large
Molecules in Solution, Cambridge University Press, Cambridge, 1980.
5. Tanford, C., Physical Chemistry of Macromolecules, Wiley, New York,
1961.
6. Yau, W. W., Kirkland, J. J., and Bly, D. D., Modern Size Exclusion
Liquid Chromatography, Wiley, New York, 1979.
tE. P. Otocka.^cc. Chem. Res. 6:348 (1973).
10
Ught Scattering by Polymer Solutions
Nature, and Nature's Laws lay hid in Night.
God said, Let Newton be! and All was Light.
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