Chemistry Reference
In-Depth Information
(ii)
What is the change in the number of average degree of
polymerization?
8-9
Consider the chain transfer reactions that occur in the radical-initiated
homopolymerizations of isopropenyl acetate (8-9-1) and methacrylonitrile
(8-9-2). Which monomer yields high-molecular-weight polymers in con-
ventional free-radical polymerizations? Explain the difference.
CH
3
CH
2
R
R
H
+
H
2
C
C
O
C
CH
3
+
H
2
C
C
O
C
CH
3
O
O
8-9-1
CH
3
CH
2
R
R
H
+
H
2
C
C
CN
+
H
2
C
C
CN
8-9-2
8-10
Vinyl acetate was polymerized in a free-radical reaction. The initial mono-
mer concentration was 1 mol/liter and its concentration after 1 h was
0.85 mol/liter. Chloroform was present as a chain transfer agent, with con-
centrations 0.01 mol/liter at time zero and 0.007 mol/liter after 1 h. What
is the chain transfer constant
C
in this case?
8-11
An engineer is studying the azodiisobutyronile-initiated polymerization of
butyl acrylate in solution. She wants to change the monomer and initiator
concentrations so as to double the initial steady-state rate of polymeriza-
tion without changing the number average degree of polymerization of the
polymer or the reaction temperature. How should she proceed?
References
[1] N.C. Billingham, A.D. Jenkins, in: A.D. Jenkins (Ed.), Polymer Science, vol. 1,
American Elsevier, New York, 1972.
[2] This is strictly true only for nonbranched chain reactions like polymerizations. In
branching chain reactions, the number of active sites may increase during a propaga-
tion step. An example is H
1
O
2
-
HO
1
O
in hydrogen
oxygen flames. Such
reactions could not be employed in a controllable polymerization and need not be con-
sidered here.
[3] C.S. Sheppard, Encycl. Polym. Sci. Technol. 11 (1987) 1.
[4] A.V. Tobolsky, C.E. Rogers, R.D. Brickman, J. Am. Chem. Soc. 82 (1960) 1277.
[5] S.C. Ng, K.K. Chee, J. Polym. Sci., Polym. Chem. Ed. 20 (1982) 409.
[6] B. Baysal, A.V. Tobolsky, J. Polym. Sci. 8 (1952) 529.
[7] R.A. Gregg, F.R. Mayo, Discuss. Faraday Soc. 2 (1947) 328.
