Re-formation reaction of cyclic nitroxide-based alkoxyamines: Steric and polar/stabilization effects

Article abstract of DOI:10.1002/hlca.200690217

In nitroxide-mediated radical polymerization, the polymerization times decrease with the increasing re-formation rate constant of the C-ON bond (→ alkoxyamine) between the growing polymer chain and the nitroxide radical. The factors influencing the re-formation rate constant are of considerable interest, but up to now, the polar/stabilization effects have not been addressed thoroughly. The combination of new data with previously reported data now showed that the re-formation rate constant k_c increases with the increasing polar character of the substituents attached to the nitroxide moiety. The polar/stabilization effects are weaker for the re-formation than for the homolysis of the C-ON bond, and may be mainly attributed to the relocation of the odd electron onto the O-atom of the N-O moiety, i.e., the stabilization of the nitroxide moiety. Hence, it is possible to predict the values of k _c by combining both the polar/stabilization (σ₁) and steric effects (E_s¹), i.e., log(k_c/M ^-1 s^-1)=9.86+0.57·σ₁+0. 40·E_s.

Full text of DOI:10.1002/hlca.200690217

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330
Helvetica Chimica Acta – Vol. 89 (2006)
Re-formation Reaction of Cyclic Nitroxide-Based Alkoxyamines: Steric and
Polar/Stabilization Effects
†a
b
c
by Hanns Fischer ), Sylvain R. A. Marque* ), and Peter Nesvadba )
a) University of Zurich, Winterthurerstrasse 190, CH-8057Zurich
b) UMR 6517case 542, UniversitØ de Provence, Avenue Escadrille Normandie-Niemen,
F-13397Marseille Cedex 20 (fax: +33-491288758; e-mail: sylvain.marque@up.univ-mrs.fr)
c
)
Ciba Specialty Chemicals Inc., Schwarzwaldallee 215, CH-4002 Basel
†
Deceased on February 22, 2006
Dedicated to Professor Hanns Fischer for his invaluable contribution in the fields of nitroxide-mediated
polymerization and radical chemistry
In nitroxide-mediated radical polymerization, the polymerization times decrease with the increasing
re-formation rate constant of the CꢀON bond (! alkoxyamine) between the growing polymer chain and
the nitroxide radical. The factors influencing the re-formation rate constant are of considerable interest,
but up to now, the polar/stabilization effects have not been addressed thoroughly. The combination of
new data with previously reported data now showed that the re-formation rate constant k increases
c
with the increasing polar character of the substituents attached to the nitroxide moiety. The polar/stabi-
lization effects are weaker for the re-formation than for the homolysis of the CꢀON bond, and may be
mainly attributed to the relocation of the odd electron onto the O-atom of the NꢀO moiety, i.e., the sta-
bilization of the nitroxide moiety. Hence, it is possible to predict the values of k by combining both the
c
1
s
ꢀ1 ꢀ1
polar/stabilization (s ) and steric effects (E ), i.e., log(k /M
s )=9.86+0.57· s +0.40·E .
I s
I
c
Introduction. – Since the seminal work of Rizzardo [1][2] and Georges [3], nitro-
xide-mediated radical polymerization (NMP) has often been used for the synthesis
of living polymers and copolymers with narrow polydispersities and controlled molec-
ular masses and architecture [4–6]. The mechanism of NMP outlined in Scheme 1
involves the cleavage of capped chain molecules (dormant species) into propagating
alkyl and persistent nitroxide radicals (k ). The propagating radicals grow by monomer
d
addition (k ) and form longer dormant chains by cross-coupling with the nitroxide rad-
p
icals (k ). Simultaneously, the usual self-termination (k ) of the propagating radicals
c
t
into unreactive polymer products takes place. This removes the propagating radicals
and increases the concentration of nitroxide radicals over time; the cross-coupling reac-
tion (k ), therefore, dominates over self-termination [7][8]. For an extended time
c
range, a quasi-equilibrium of the reversible cleavage exists which is characterized by
weakly time-dependent radical concentrations and a large excess of the persistent rad-
icals over the propagating radicals.
For the well-controlled and living radical polymerization of a given monomer with
propagation and termination rate constants k and k , the rate constants of the reversi-
p
t
ble cleavage k and k must fall into proper ranges [7–9]. In general, one aims at rela-
d
c
ꢀ
2006 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 89 (2006)
2331
Scheme 1. Simplified Scheme of Nitroxide-Mediated Polymerization (NMP). M=monomer.
tively large equilibrium constants K=k /k because they yield large propagating-radi-
d
c
cal concentrations, and, hence, comparatively fast monomer conversion [7–9]. Further-
more, at a given time, the polydispersity index is smaller for larger k and k . Conse-
d
c
quently, the determination of K and k has recently attracted considerable attention
d
for both polymeric [10][11] and low-molecular-mass systems [12–17].
Up to now, most of the studies in this domain were devoted to the measurements of
kd and to the analysis of the effects of the subtituents attached to the nitroxide moiety
on the strength of the CꢀON bond [18]. However, it has appeared in the literature that
values of k may play an important role in the fate of the polymerization [19][20]. Sie-
c
genthaler and Studer [20] have shown that the polymerization was ca. five times as fast
with B than with A (Fig. 1) whereas kd,A =kd,B but kc,A >40·k . Therefore, it is timely
c,B
to analyze thoroughly the effects involved in the re-formation of alkoxyamines. This
has been partially addressed by Ingold and co-workers [21][22] for a few nitroxide rad-
icals with a large set of alkyl radicals and solvents, but very few radicals were of interest
for the polymerization. Fischer and co-workers [23][24] measured k for both nitroxide
c
and alkyl radicals used in NMP and revealed very weak temperature dependences; they
showed with a small series of nitroxide radicals that k decreased with increasing con-
c
gestion around the nitroxide moiety. In contrast to the many data gathered concerning
the CꢀON bond homolysis [16][17] – polar, stabilization, and steric effects for nitro-
xide and alkyl fragments, long-range steric and polar effects, intramolecular H-bonding,
anomeric and anchimeric effects – and to the predictive relationships developed for kd,
not so many data have been collected concerning the re-formation reaction, and no pre-
dictive models have been developed for k . Therefore, using the new k measured in this
c
c
work for nitroxide radicals 11, 12, 14, and 15, and those given in the literature [22–25]
for nitroxide radicals 1–10, 13, and 16 (Table 1), we propose to rationalize the polar and
steric effects of the substituents attached to the nitroxide moieties for the scavenging of
the 1-phenylethyl radical in terms of a bi-parameter relationship (electrical Hammett
constant s for the polar effect, and modified Taft steric constant E for the steric effect).
I
s
Fig. 1. Alkoxyamines A and B

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332
Helvetica Chimica Acta – Vol. 89 (2006)
Experimental. – The synthesis and the properties of nitroxide radicals 11 [26], 12 [27], and 14 and 15
28] have been described elsewhere. The radicals were analytically pure. a,a’-Dimethyldibenzyl ketone
=2,4-diphenylpentan-3-one) and dicumyl ketone (=2,4-dimethyl-2,4-diphenylpentan-3-one;
[
(
purity>98%) were prepared according to [29]. The solvent (tert-butyl)benzene (Fluka; >99%) was dis-
tilled once before use.
For the determination of the cross-reaction rate constants, 1-phenylethyl and cumyl radicals were
produced by laser flash photolysis (308 nm) of the corresponding ketones in solutions containing the
nitroxide radicals, and their decay was monitored over time at l 321 nm. All the details of the technique
has been described earlier [23].
Results. – Cross-coupling rate constants k were measured for a number of structur-
c
ally related alkoxyamines, i.e., for the nitroxide radicals 1–19 (Table 1). The rate con-
stants were found to be clearly dependent on the substituent pattern at the C(a) atoms
shielding the NO group. The data showed, that k was decreasing with increasing steric
c
demand of the substituents. The cross-coupling rate constants k of the reaction of 17,
c
18, and 4 with the cumyl radical illustrates another effect (Table 1). The two spiro-cy-
clohexane moieties in the a,a’-positions of the piperidinyloxy moiety of 17 were
assumed to be bulkier than the four Me groups of TEMPO (=2,2,6,6-tetramethylpiper-
idin-1-yloxy; 4). Therefore, one would expect a smaller k for 17 than for TEMPO
c
7
ꢀ1 ꢀ1
(kc =5.2·10
M
s ) [23]. In fact, k for 17 is two times larger than that for TEMPO,
c
which exemplifies well the importance of the polar effect of electron-withdrawing
groups (keto group of 17, sI;CH2COCH2 =0.11) attached to the nitroxide moiety. This is
7
ꢀ1 ꢀ1
confirmed by the very similar k for 18 and 19 (k =1.1·10
M
s ) [23], where the
c
c
four Ph groups of 18 are expected to be bulkier than the four Et groups of 19. Indeed,
the electron-withdrawing capacity (sI,Ph =0.12) of the Ph group – larger than the one of
Et group (sI,Et =ꢀ0.01) – balances the bulkiness of the Ph groups which hamper the
approach to the reactive center. The polar effect is likely to disfavor the mesomeric
form D with respect to form C (Scheme 2), i.e., facilitating the relocation of the odd
electron onto the O-atom of the nitroxide moiety, and, hence, increasing k . Therefore,
c
the polar and stabilization effect cannot be separated into elementary components.
Scheme 2. Mesomeric Forms C and D of the Nitroxide Radical
The cross-coupling rate constants k for 11, 12, 14, and 15 with the 1-phenylethyl
c
radical were measured at 296, 323, and 373, or 393 K (Table 1). As already observed,
kc increases only very little with the temperature [22][23][30]. For 11, 12, and 14, for
which the steric effect is expected to be constant, k decreases weakly along the series
c
in parallel with the decreasing electron-withdrawing capacity [31] of the substituent
(s
=0.10, s
=0.04, s
=0.02), in line with the
I;MeCHCðOÞCH2
I;MeCHCHðOAcÞCH2
I;MeCHCHðOHÞCH2
observations done for 17 and 18.
However, for nitroxide radicals 1–16, a shotgun-like plot is observed for log k vs. s
c
I
(
Fig. 2, Table 1). On the other hand, the plot of log k vs. E (Fig. 3, Table 1) is linear for
c s
3
, 5, 8–10, 13, and 16, as already reported [31]. The downward deviations for nitroxide

Helvetica Chimica Acta – Vol. 89 (2006)
2333
a
Table 1. Cross-Coupling Rate Constants k for the 1-Phenylethyl Radical (MeCH(Ph)C) ) and Nitroxide
c
Radicals 1–16 in (tert-Butyl)benzene at Various Temperatures, and the Corresponding Electrical Ham-
mett Constants sI,n and Modified Taft Steric Constants E . Cross-Coupling Rate Constants k for the
s,n
c
b
Cumyl Radical (Cum) ) and Nitroxide Radicals 4 and 17–19 in (tert-Butyl)benzene at Various Temper-
atures
c
sI,nd)
Es,ne)
Nitroxide radical
Alkyl radi- kc
A
H
R
U
G
A
T
E
N
(323
kc
K) )/
10
A
H
R
N
(373
Ref.
c
7
ꢀ1 ꢀ1
c
c
cal
10
7
ꢀ1 ꢀ1
7
ꢀ1 ꢀ1
M
M
s
s
f
g
h
h
i
j
1
2
MeCH(Ph)C 43.0 ) )
– )
– )
ꢀ0.04 ) ꢀ2.94 ) [22]
f
k
h
h
l
m
MeCH(Ph)C 26.0 ) )
– )
– )
0.52 ) ꢀ4.20 ) [25]
3
4
5
MeCH(Ph)C 26.0
MeCH(Ph)C 22.0f)
MeCH(Ph)C 19.0
29.0
23.0
21.0
30.0
0.33 ꢀ4.20 [24]
ꢀ0.06 ꢀ4.20 [22][23]
0.33 ꢀ4.45 [24]
h
– )
22.0
f
n
h
h
6
7
8
MeCH(Ph)C 17.0 ) )
– )
– )
0.00 ꢀ4.20 [25]
0.08 ꢀ4.20 [24]
0.33 ꢀ4.70 [24]
f
o
h
h
MeCH(Ph)C 15.0 ) )
– )
– )
MeCH(Ph)C 12.0
14.0
15.0

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334
Helvetica Chimica Acta – Vol. 89 (2006)
Table 1 (cont.)
c
sI,nd)
Es,ne)
Nitroxide radical
Alkyl radi- kc
A
H
R
U
G
A
H
R
U
G
kc
K) )/
10
A
H
R
U
G
Ref.
c
7
ꢀ1 ꢀ1
c
c
cal
10
s
s
9
MeCH(Ph)C 10.0
MeCH(Ph)C 10.0
11.0
11.0
11.0
11.0
0.33 ꢀ5.21 [24]
1
0
0.33 ꢀ5.21 [24]
this
ꢀ4.70
1
1
1
2
MeCH(Ph)C 8.710.0
MeCH(Ph)C 8.1
12.0(10)
0.06
work
this
0.00 ꢀ4.70
work
9.3
10.0(10)
8.6
1
1
1
3
4
5
MeCH(Ph)C 6.8
MeCH(Ph)C 6.1n)
MeCH(Ph)C 5.8
7.8
7.1
6.4
0.33 ꢀ5.45 [24]
this
work
7.7(2)p) ꢀ0.02 ꢀ4.70
6.7(2)p) ꢀ0.01 ꢀ5.21
this
work
1
6
MeCH(Ph)C 4.0
5.6
5.6
0.33 ꢀ6.20 [24]
4
CumC
5.2
5.75.5
p)
ꢀ0.06 ꢀ4.20 [22][23]

Helvetica Chimica Acta – Vol. 89 (2006)
2335
Table 1 (cont.)
c
sI,nd)
Es,ne)
Nitroxide radical
Alkyl radi- kc
A
H
R
U
(296K) )/ k
A
H
R
U
G
kc
K) )/
10
A
T
E
N
(373
Ref.
c
7
ꢀ1 ꢀ1
c
c
cal
10
M
s
K) )/
7
ꢀ1 ꢀ1
M
1
0
s
s
this
work
14.0(10)p)
– )
q
– )
q
1
7
CumC
11.0(10)
12.0(10)
this
work
1.5(2)n)
1.1
1.7(4)
1.2
2.6(4)p)
0.9p)
– )
q
– )
q
1
1
8
9
CumC
CumC
q
q
– )
– )
[23]
a) MeCH(Ph)C=1-phenylethyl radical. ) CumC=cumyl radical=1-methyl-1-phenylethyl radical. ) Errors
b
c
d
e
given in parentheses on the last unit. ) Given by Eqn. 2 and those in [15][31][32]. ) Given by Eqns. 3 and
f
4
, see text; r (H)=0.32, r (Me)=0.0, r (Et)=ꢀ0.38, see [33]. ) At 293 K. It was assumed that the differ-
i
i
i
g
7
ꢀ1 ꢀ1
M
ence of temperature was not significant. ) Given in isooctane (=2-methylheptane), k =86.0·10
s .
c
h
i
j
)
Not measured. ) s =0, sI,Me =ꢀ0.01, see [32]. ) It was assumed that the rings out of the nodal plane
I,H
k
7
ꢀ1 ꢀ1
l
M
were not more sterically demanding than the Me group. ) Measured in MeCN, k =15.0·10
s . ) It
c
m
was assumed [31] that s
ꢁs
=0.28. ) It was assumed that the spiro-cyclohexane
I;ðPhCH2 ÞðMeÞNCO
I;Me2NCO
rings in positions a,a’ were not more sterically demanding than the Me group due to the peculiar confor-
2
n
7
mation of the ring generated by the presence of two sp C-atoms [31]. ) Measured in MeCN, k =9.8·10
c
ꢀ
1
ꢀ1
o
7
ꢀ1 ꢀ1
p
q
M
s
. ) Measured in isooctane, k =30.0·10
M
s . ) Measured at 393 K. ) Not given.
c
radicals 1, 6, 7, 11, 12, and 15 are likely due to the polar/stabilization effect. Therefore,
as for the case of the homolysis, the variation of log k should be described by Eqn. 1
c
with the electrical Hammett constant [32] sI,n accounting for the stabilization/polar
effect [15][31] and the modified Taft steric constant [33] Es,n accounting for the conges-
tion around the nitroxide moiety [15][31]. The values of s , which is the sum of the s
I,n
I
values for each substituent, and Es,n (Fig. 4) are given by Eqns. 2–4 and presented in
Table 1. It has to be mentioned that the larger the group R , the smaller r , thus r cor-
i
i
1
responds to the small size group, r to the medium size group, and r to the large size
2
3
group.
ꢀ
1
ꢀ1
ꢀ1 ꢀ1
log(k /M s )=log(k /M s )+1 ·s +d·E
s,n
(1)
c,n
c,0
I
I,n
X6
s =
s (R )
(2)
(3)
I,n
I
i
i¼1
A
B
s;n
E =E +E
s,n
s;n

2
336
Helvetica Chimica Acta – Vol. 89 (2006)
ꢀ1
ꢀ1
Fig. 2. Plot of log(k /M
s ) vs. sI,n for molecules 1–16
c
ꢀ1
ꢀ1
Fig. 3. Plot of log(k /M
s
) vs. Es,n for molecules 1–16.
&
: Data for nitroxide radicals 3, 5, 8–10, 13,
c
and 16; *: data for 1, 2, 4, 6, 7, 11, 12, 14, and 15.
A or B
s;n
E
=ꢀ2.104+3.429·r
A
T
E
N
(R )+1.978·r
A
T
E
N
A
T
E
N
(4)
1
1
2
2
3
3
For the homolysis of the alkoxyamines corresponding to the nitroxide radicals listed
in Table 1, k exhibited a strong dependence on the ring conformation [31]. Assuming
d
that the steric constants E determined for the cyclic nitroxide moiety of alkoxyamines
s
hold for nitroxide radicals, Eqn. 1 was applied, and yielded (Eqn. 5, Table 2) not quite
good statistical values. The slope for the steric effect (d=0.29) was different from the
one previously [24] determined (d=0.36) for 3, 5, 8–10, 13, and 16. Therefore, the ring

Helvetica Chimica Acta – Vol. 89 (2006)
2337
Fig. 4. Examples of polar/stabilization and steric effects in nitroxide radicals
Table 2. Parameters 1 and d, and Statistical Outputs for Eqn. 1 Applying Es,n Given in [15][31] (Eqn. 5),
and Applying New Estimated Es,n (Eqns. 6 and 7)
log kc0a)
1 )
a
da)
Nb)
R2 c
)
s )
d
t )
e
F f
)
N
Eqn.
I
5g
)
)
8.97(17)
0.88(26)
0.57(13)
0.66(18)
0.29(5)
14h)
0.75
0.91
0.85
0.13
0.09
0.10
99.40 )
9
i
16k)
68l)
26o)
j
9.98 )
6g
9.85(15)
9.82(26)
0.40(3)
0.38(5)
16
99.92 )
i
j
9
9.99 )
7m
)
12n)
99.50 )
i
j
9
9.99 )
a) Errors in parentheses given on the last digit. ) Number of data. ) Square of the linear regression coef-
b
c
d
e
f
g
h
ficient. ) Standard deviation. ) Student t-test. ) F-Test. ) At 296 K. ) E values were not available for 1
s,n
i
j
k
l
m
n
and 2. ) t-Test for 1 . ) t-Test for d. ) F-Test at 0.05%. ) F-Test at 0.01%. ) At 323 K. ) Values of k for 1,
, 6, and 7 were not available. ) F-Test at 0.02%.
I
c
o
2
does not have the same influence on k than on k . Thus, it was assumed that the cyclic
c
d
strain exerts no significant influence on the congestion around the nitroxide moiety.
Then, it was assumed that whatever the ring size – five- or six-membered rings – and
substituents at the positions other than the positions a and a’, the ring exhibited the
same steric demand for all molecules presented in Table 1. For the sake of simplicity,
it was assumed that the groups or ring on the nodal plane of the nitroxide moiety exhib-
ited identical steric demand than the Me group, and thus, the r values of these groups/
rings were taken as r and equal to zero [34]. Finally, applying Eqns. 1–4 to molecules
1
1
–16 yielded Eqns. 6 (T 296 K) and 7 (T 323 K) with good statistical outputs (Table 2).
Regression parameters were improved when molecules 4 and 14 were removed. The
upward deviation of 4 is due to a k value two times higher than expected from Eqn.
c
6
. The downward deviation of 14 is due to a k value 1.5 times lower than expected
c
from Eqn. 6. It is worthy to mention that the y-intercept (log k ) corresponds to the
c,0
typical value of k observed for diffusion-controlled reactions.
c
Discussion. – As mentioned above, the scavenging of the cumyl radical by 17 and 18
emphasizes well the polar effect due to the presence of electron-withdrawing groups
(EWGs) close to the nitroxide moiety. That is, bulky groups such as phenyl or spiro-cy-
clohexane groups hamper the approach of the cumyl radical to the nitroxide moiety and
thus decrease k , whereas the presence of an EWG attached to the nitroxide moiety
c
balances or overbalances the steric effect as for 18 and 19 and as for 17 and

2
338
Helvetica Chimica Acta – Vol. 89 (2006)
TEMPO, respectively (see Results). In fact, EWGs destabilize the form D in favor of
form C, and thus facilitate the relocation of the odd electron onto the O-atom of the
nitroxide function (Scheme 2). Hence, the polar and stabilization effects cannot be
studied separately. However, this should not be the case for a nitroxide moiety carrying
aromatic or vinylic fragments, i.e., p-system attached to the nitroxide moiety, for which
strong delocalization of the odd electron should be observed independently of the pres-
ence of EWG. Such a trend is also observed for the scavenging of the 1-phenylethyl rad-
ical by nitroxide radicals 1–16. Thorough studies of rate constants k for the CꢀON
d
bond homolysis showed that the steric effect was strongly dependent on the size of
the ring, on the substituents, and on the hybridization of the atoms of the ring
[
15][31]. On the other hand, for the re-formation of the alkoxyamine, k does not
c
depend on the ring size or on the ring substituents, as shown by the poor regression
Eqn. 5, Table 2) obtained with the E values applied to k . Thus, a bi-parameter corre-
(
s
d
lation (s and E ) was performed, and the expected straight line was observed (Eqn. 6 in
I
s
Table 2, Fig. 5). By using the weighting equations [16][35], the polar/stabilization and
steric effects are given at 27% and 73%, respectively, for Eqn. 6 at 296 K, at 35%
and 65%, respectively, for Eqn. 7 at 323 K. Hence, the polar/stabilization effect is the
minor effect (ca. 30%) although still important. As already mentioned [24], the steric
ꢀ
1
ꢀ1
Fig. 5. Log(k /M
s ) vs. Eqn. 1 at 293 K for molecules 1–16
c
effects for the re-formation and the homolysis of the CꢀON bond are anti-correlated,
as shown by the positive sign (Eqn. 6, Table 2) for d and the negative sign for d (Eqn. 8)
d
[
15][31], respectively. And, as expected, the polar/stabilization effects for the re-forma-
tion and the homolysis of the CꢀON bond are anti-correlated, as shown by the positive
sign for 1 (Eqn. 6, Table 2) and the negative sign for 1 (Eqn. 8) [15][31], respectively.
I
I,d
The positive sign for the steric parameter means that the reaction is retarded by the
increasing size of the substituents attached to the nitroxide moiety, that is, in the tran-

Helvetica Chimica Acta – Vol. 89 (2006)
2339
sition state (TS), the approach of the alkyl radical to the reactive center is hampered by
bulky groups, i.e., the TS is destabilized. The positive sign of the polar/stabilization
parameter means that the reaction is accelerated by increasing the electron-withdraw-
ing capacity of the substituents attached to the nitroxide moiety. The presence of
EWGs destabilizes the nitroxide moiety, thereby, destabilizing the initial state and
thus TS, by virtue of the Hammond principle. However, the destabilizing effect of
EWGs is overmatched by the relocation of the odd electron onto the O-atom of the
nitroxide moiety, i.e., the increased weight of form C, which makes the coupling easier
in the TS. As the polar/stabilization and steric constants were estimated in the same
way for both the re-formation and the homolysis of the CꢀON bond, the comparison
of the absolute values of the parameters was made possible. It comes out that the re-
formation reaction is roughly two times less sensitive to the size of the substituents
and roughly 5 times less sensitive to the electron-withdrawing capacity of the substitu-
ents than the homolysis is.
ꢀ
1
log(k /s )=ꢀ5.73 ꢀ2.81·s ꢀ0.83·E
(8)
d
I
s
Conclusions. – Like the rate constants k for the homolysis of the alkoxyamines
d
CꢀON bond, the rate constants k for the re-formation of the CꢀON bond are well
c
accounted for by the polar/stabilization and steric effects. Hence, with Eqn. 6, it is pos-
sible to predict the values of k at first glance on the structure. To apply Fischerꢁs phase
c
diagrams [7][9], it is now possible to know the values of k and k by combining the rela-
d
c
tionships developed in this work and in the literature. Such diagrams are very useful to
determine the fate of NMP.
S. R. A. M. is deeply grateful to Prof. Fischer for the many fruitful discussions during his postdoctoral
fellowship in the Physical-Chemistry Institute at the University of Zurich. The authors thank Dr. Jens
Sobek for providing the k values.
c
REFERENCES
[
1] D. H. Solomon, E. Rizzardo, P. Cacioli, U.S. Pat. 4,581,429, 1986; Eur. Pat. Appl. 135280, 1985
Chem. Abstr. 1985, 102, 221335q).
(
[
[
[
[
2] E. Rizzardo, Chem. Aust. 1987, 54, 32.
3] M. K. Georges, R. P. N. Veregin, P. M. Kazmaier, G. K. Hamer, Macromolecules 1993, 26, 2987.
4] C. J. Hawker, A. W. Bosman, E. Harth, Chem. Rev. 2001, 101, 3661, and refs. cit. therein.
5] Y. Gnanou, D. Taton, in ꢂHandbook of Radical Polymerizationꢁ, Eds. K. Matyjaszewski, T. P. Davis,
Wiley-Interscience, Hoboken, 2002, p. 775.
[
6] G. Moad, D. H. Solomon, ꢂThe Chemistry of Radical Polymerizationꢁ, 2nd edn., Elsevier, Amster-
dam, 2006.
[
[
[
7] H. Fischer, Chem. Rev. 2001, 101, 3581.
8] A. Goto, T. Fukuda, Prog. Polym. Sci. 2004, 29, 329.
9] H. Fischer, M. Souaille, Chimia 2001, 55, 109.
[
[
10] A. Goto, T. Fukuda, Macromol. Chem. Phys. 2000, 201, 2138, and refs. cit. therein.
11] O. Guerret, J.-L. Couturier, F. Chauvin, H. El-Bouazzy, D. Bertin, D. Gigmes, S. Marque, H. Fischer,
P. Tordo, ACS Symp. Ser. 2003, 854, 412, and refs. cit. therein.
[
[
[
12] G. Moad, E. Rizzardo, Macromolecules 1995, 28, 8722.
13] D. Benoit, V. Chaplinski, R. Braslau, C. J. Hawker, J. Am. Chem. Soc. 1999, 121, 3904.
14] C. Knoop, A. Studer, J. Am. Chem. Soc. 2003, 125, 16327.

2
340
Helvetica Chimica Acta – Vol. 89 (2006)
[
[
[
[
[
15] S. Marque, J. Org. Chem. 2003, 68, 7582.
16] D. Bertin, D. Gigmes, S. R. A. Marque, P. Tordo, Macromolecules 2005, 38, 2638.
17] E. Beaudoin, D. Bertin, D. Gigmes, S. R. A. Marque, D. Siri, P. Tordo, Eur. J. Org. Chem. 2006, 1755.
18] D. Bertin, D. Gigimes, S. R. A. Marque, Recent Res. Dev. Org. Chem. 2006, in press.
19] Y. Guillaneuf, D. Gigmes, S. R. A. Marque, P. Tordo, D. Bertin, Macromol. Chem. Phys. 2006, 207,
1278.
[
[
[
[
[
20] K. O. Siegenthaler, A. Studer, Macromolecules 2006, 39, 1347.
21] A. L. J. Beckwith, V. W. Bowry, K. U. Ingold, J. Am. Chem. Soc. 1992, 114, 4983.
22] V. W. Bowry, K. U. Ingold, J. Am. Chem. Soc. 1992, 114, 4992.
23] J. Sobek, R. Martschke, H. Fischer, J. Am. Chem. Soc. 2001, 123, 2849.
24] S. Marque, J. Sobek, H. Fischer, A. Kramer, P. Nesvadba, W. Wunderlich, Macromolecules 2003, 36,
3
440.
25] W. G. Skene, J. C. Scaiano, N. A. Listigover, P. M. Kazmaier, M. K. Georges, Macromolecules 2000,
3, 5065.
[
3
[
[
[
[
[
[
[
[
[
26] P. Nesvadba, L. Bugnon, R. Sift, J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 3332.
27] P. Nesvadba, M.-O. Zink, A. Kramer, DE 10113209, 2001 (Chem. Abstr. 2001, 135, 273355).
28] P. Nesvadba, M.-O. Zink, A. Kramer, DE 19909767, 1999 (Chem. Abstr. 1999, 131, 229170).
29] B. H. Baretz, N. J. Turro, J. Am. Chem. Soc. 1983, 105, 1309.
30] J. Chateauneuf, J. Lusztyk, K. U. Ingold, J. Org. Chem. 1988, 53, 1629.
31] H. Fischer, A. Kramer, S. R. A. Marque, P. Nesvadba, Macromolecules 2005, 38, 9974.
32] M. Charton, Prog. Phys. Org. Chem. 1981, 13, 119.
33] T. Fujita, C. Takayama, M. Nakajima, J. Org. Chem. 1973, 38, 1623.
34] D. Zubenko, Y. Tsentalovicha, N. Lebedeva, I. Kirilyuk, G. Roshchupkina, I. Zhurko, V. Reznikov,
S. R. A. Marque, E. Bagryanskaya, J. Org. Chem., submitted.
[
35] J. Shorter, ꢂCorrelation Analysis of Organic Reactivityꢁ, Research Studies Press, Chichester, 1982, p. 73.
Received April 28, 2006