Page 391 - Elements of Chemical Reaction Engineering Ebook

362 Nonelementary Reaction Kinetics Chap. 7

For monofunctional init.,&; xs the reaction sequence between monomer M
and initiator I is

for example,

H
I
(CH,),C * + CH,=CHCl + (CH,),C CH2C *
I I 1
CN CN C1

Propagation. The propagation sequence between a free radical R1 with a
monomer unit is

Propagation

In general,

Assumption of equal
reactivity

for example,

H H
I I
(CH3),C(CH2CHCl)JCH2C. + CH,=CHCI ---+ (CH3),C(CH2CHCl),+,CH2C.
I I I I
CN Cl CN c1
The specific reaction rates kp are assumed to be identical for the addition of
each monomer to the growing chain. This is usually an excellent assumption
once two or more monomers have been added to R, and for low conversions of
monomer. The specific reaction rate k, is often taken to be equal to kp.

Chain Transfer. The transfer of a radical from a growing polymer chain can
occur in the following ways:

1. Transfer to a monomer:

Rj+ M

Here a live polymer chain of j monomer units tranfers its free radical
to the monomer to form the radical R, and a dead polymer chain of j
monomer units.