Page 393 - Elements of Chemical Reaction Engineering Ebook

364 Nonelementary Reaction Kinetics Chap. 7

The steps in free-radical polymerization reaction and the corre-
sponding rate laws are summarized in Table 7-3. For the polymeriza-
tion of styrene at 80°C initiated by 2,2-azobisisobutyronitrile the rate
constants9 are

Initiation k.,, = 1.4 x 10-3 s-1 k,,, = 3.2 X loh2 dm3/mol.s
propagati~
Transfer kp = 4.4 X lo2 dm3/mol.s k, = 1.2 X lo8 dm3/mol.s
Termination
k, = 2.9 X dm3/mol s kd = 0
*

TABLE 1-3
Rate Law
Initiation:
I, 4, 21
I+M -% R,
Propagation:
R, + M --% Rj+,
Chain transfer to:
Monomer:
Rj+ M -% Pj+R,
Another species:
Rj+C -& Pj+ R,
Solvent:
Rr + S Pj+R,
Termination:
Addition:

Disproportionation:

Qpical initial concentrations for the solution polymerization of styrene are
0.01 M for the initiator, 3 M for the monomer, ,and 7'M for the solvent.

7,3,2,2 Dweloplng the Rate Law8 for the Net Rate
of Reactlon

We begin by considering the rate of formation of the initiator radical Z.
Because there will always be scavenging or recombining of the primary radi-
cals, only a certain fraction f will be successful in initiating polymer chains.

D. C, Timm and J, W. Rachow, ACS Symposium Series 133, H. M. Hulhrt, ed., 1974,
p. 122.