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remaining hexad features. Use the value of pm given to calculate the
probabilities of the unsplit tetrads (see Problem 11) and on this basis
assign the features listed above to the appropriate tetrads. Which of the
tetrads appears to be split into hexads?
13. The fraction of sequences of the length indicated below have been
measured t for a copolymer system at different feed ratios:
[Mi ]/[M2 ] P(MO P(M ! M i ) P(M1M1M1)
3 0.168 0.0643 0.0149
4 0.189 0.0563 0.0161
9 0.388 0.225 0.107
19 0.592 0.425 0.278
From appropriate ratios of these sequence lengths, what conclusions
can be drawn concerning terminal versus penultimate control of addition?
14. The following are experimental tacticity fractions of polymers
prepared from different monomers and with various catalysts. On the basis
of Fig. 7.9, decide whether these preparations are adequately described
(remember to make some allowance for experimental error) by a single
parameter pm or whether some other type of statistical description is
Temperature Fraction of polymer
Catalyst Solvent (░C) Iso Hetero Syndio
Methyl methacrylate t
Thermal Toluene 60 8 33 59
n-Butyl lithium Toluene -78 78 16 6
Ű-Butyl lithium Methyl isobutyrate -78 21 31 48
TiCl4 Toluene -78 - 19 81
Et3Al/TiCl4 Benzene 25 3 35 62
Ű-Butyl lithium Cyclohexane 4 - 31 69
t K. Ito and Y. Yamashita, J. Polym. Sci. 3A.2165 (1965).
*K. Hatada, K. Ota, and H. Yuki,Polym. Lett. 5:225 (1967).
žS. Brownstein, S. Bywater, and O. J. Worsfold,Makromol. Chem. 48:127
Polymers with Microstructure
On the basis of these observations, criticize or defend the following
proposition: Regardless of the monomer used, zero-order Markov
(Bernoulli) statistics apply to all free radical, anionic, and cationic
polymerizations, but not to Ziegler-Natta catalyzed systems.
15. Replacing one of the alkyl groups in R3A1 with a halogen increases
the stereospecificity of the Ziegler-Natta catalyst in the order I > Br >
Cl> R. Replacement of a second alkyl by halogen decreases specificity.
Criticize or defend the following proposition on the basis of these
observations: The observed result of halogen substitution is consistent
with the effect on the ease of alkylation produced by substituents of
different electronegativity. This evidence thus adds credence to the
monometallic mechanism, even though the observation involves the
16. The weight percent propylene in ethylene-propylene copolymers for
different Ziegler-Natta catalysts was measuredt for the initial polymer
produced from identical feedstocks. The following results were obtained:
Catalyst Weight percent Catalyst Weight percent
components propylene components propylene
VC14 plus Al(z'-Bu)3 plus
Al(z'-Bu)3 4.5 HfCl4 0.7
CH3TiCl3 4.5 ZrCl4 0.8
Zn(C2H5)2 4.5 VOCl3 2.4
Interpret these results in terms of the relative influence of the
two components of the catalyst on the product found.
1. Alfrey, Ď., Jr., Bohrer, J. J., and Mark, H., Copolymerization,
Interscience, New York, 195 2.
2. Bovey, F. A., High Resolution NMR of Macromolecules, Academic, New
3. Bovey, F. A., and Winslow, F. H., Macromolecules: An Introduction to
Polymer Science, Academic, New York, 1979.
4. Brandup, J., Immergut, E. H., and McDowell, W. (Eds.), Polymer
Handbook, 2nd ed., Wiley, New York, 1975.
5. Ham, G. E. (Ed.), Copolymerization, Interscience, New York, 1964.
6. Koenig, J. L., Chemical Micro structure of Polymer Chains, Wiley, New
7. Odian, G., Principles of Polymerization, 2nd ed., Wiley, New York,
t F.J. Karol and W. L. Car rick ,J.Am. Chem. Soc. 83:585 (1960).
SOME PROPERTIES OF POLYMER SOLUTIONS AND THEIR RELATION TO POLYMER
The Thermodynamics of Polymer Solutions
See plastic nature working to this end The single
atoms each to other tend Attract, attracted to, the next in place Formed
and impelled its neighbor to embrace.
An Essay On Man,
The title of this chapter is somewhat misleading. In one sense it is too
broad, in another sense too restrictive. We shall really discuss in
detail only the phase separation and osmostic pressure of polymer