Propagation rate of the cationic polymerization of 2,4,6-trimethylstyrene: A linear free energy approach

Article abstract of DOI:10.1021/ma048389o

Kinetics of the reactions of benzhydryl cations with 2,4, 6-trimethylstyrene have been performed to determine its nucleophilicity parameters N = 0.68 and s = 1.09, which are comparable to styrene and considerably less nucleophilic than 4-methylatyrene, in

Full text of DOI:10.1021/ma048389o

Macromolecules 2005, 38, 33-40
33
Propagation Rate of the Cationic Polymerization of
2,4,6-Trimethylstyrene: A Linear Free Energy Approach
Herbert Mayr,* Armin R. Ofial, and Holger Schimmel
Department Chemie und Biochemie der Ludwig-Maximilians-Universita¨t Mu¨nchen,
Butenandtstrasse 5-13 (Haus F), D-81377 Mu¨nchen, Germany
Received August 4, 2004; Revised Manuscript Received October 15, 2004
ABSTRACT: Kinetics of the reactions of benzhydryl cations with 2,4,6-trimethylstyrene have been
performed to determine its nucleophilicity parameters N ) 0.68 and s ) 1.09, which are comparable to
styrene and considerably less nucleophilic than 4-methylstyrene, indicating the retarding effect of the
ortho methyl groups. Kinetic investigations of the reactions of the 2,4,6-trimethylstyryl cation 6+ and
the corresponding dimer 7+ with the reference nucleophile 2-chloropropene allow us to calculate the closely
similar electrophilicity parameters E(6+) ) 6.04 and E(7+) ) 6.16 which are considerably lower than
that of the styryl cation (E ) 9.6). As a consequence, the propagation rate constant of the cationic
polymerization of 2,4,6-trimethylstyrene is considerably lower than that of styrene. Substituting these
values into the correlation log k20 °C ) s(N + E) yields a propagation rate constant of 3 × 107 M-1 s-1
,
which has to be considered an upper limit because extra steric strain generated in the reaction of 7+
with 2,4,6-trimethylstyrene is not included in this correlation.
Introduction
ous.13,14 The carbocationic polymerization of TMeSt15
has, therefore, been used as a test system to compare
the different methods for determining propagation rate
constants in ionic polymerizations as described in this
and the following paper.16
Propagation rate constants for the carbocationic po-
lymerization of vinyl derivatives have controversially
been discussed for many years.1,2 For the polymerization
of isobutylene, propagation rate constants between 6 ×
103 and 7 × 108 M-1 s-1 have been reported,1-7 and for
the polymerization of styrene, values between 103 and
109 M-1 s-1 can be found in the literature.1,2,6-11 In all
cases, rate constants determined with low-molecular
weight model compounds were at the high end of the
published reactivity range. To exclude that macromo-
lecular carbocations differ considerably in reactivity
from their low-molecular weight analogues, we have
generated the carbocations 1a+ (Mn ≈ 2400 g mol-1) and
1b+ (M ) 195 g mol-1) in the presence of π-nucleophiles
and found that the reactivity of 1a+ was only 25%
smaller than that of 1b+.12
Rates of the reactions of carbocations with nucleo-
philes, including olefins, can be described by eq 1, where
k represents the second-order rate constant in M-1 s-1
,
E is the electrophilicity parameter of the carbocation,
N is the nucleophilicity parameter of the olefin, and s
is the corresponding nucleophile-specific slope
parameter.17-23
Since different kinetic behavior of high and low
molecular weight compounds was thus excluded, the
most likely origin for the deviating propagation rate
constants is the uncertainty in the concentration of the
active species.
Though the propagating species of carbocationic sty-
rene (St) polymerization 2+ can be detected by UV-
spectrometry,9 its ability to undergo indane cyclization
with formation of carbocations with similar absorption
maxima may cause problems in determining its con-
centration. Since the o-methyl groups in 2,4,6-trimeth-
ylstyrene (TMeSt) inhibit intramolecular cyclizations,
determination of the concentration of the propagating
carbocation 3+ in its polymerization is less ambigu-
log k20 °C ) s(E + N)
(1)
To employ this equation for calculating the propaga-
tion rate constant kp of the carbocationic polymerization
of 2,4,6-trimethylstyrene, the electrophilicity parameter
E of the propagating carbocation 3+ as well as the
reactivity parameters N and s of 2,4,6-trimethylstyrene
are needed.
Nucleophilic Reactivity of
2,4,6-Trimethylstyrene
In previous work, diarylcarbenium ions (benzhydryl
cations) have been recommended as reference electro-
philes for determining the reactivity parameters N and
s of many types of nucleophiles.23-28 We have now used
* Corresponding author. Herbert.Mayr@cup.uni-muenchen.de.
10.1021/ma048389o CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/15/2004

34 Mayr et al.
Macromolecules, Vol. 38, No. 1, 2005
Table 1. Eyring Activation Parameters for the Reactions of 2,4,6-Trimethylstyrene with the Benzhydrylium Ions 4a+,
4b+, and 4c+ (in CH2Cl2)
a From ref 23.
Scheme 1. Lewis Acid Induced Reactions of TMeSt
with Benzhydryl Chlorides 4-Cl
parameter s ) 1.09 for TMeSt. These parameters, as
well as the underlying rate constants depicted in Figure
2 reveal that TMeSt and styrene show almost identical
nucleophilic reactivities. The increase of nucleophilicity
due to the electron donating effect of the three methyl
groups is almost completely canceled by the distortion
this method for determining N and s of 2,4,6-trimeth-
ylstyrene (TMeSt).
Scheme 1 shows that the benzhydryl chlorides 4a-Cl
and 4b-Cl combine with TMeSt in the presence of zinc
chloride and benzyltriethylammonium chloride (to sup-
press polymerization) to give fair yields of the addition
products 5a and 5b. These products are formed as
mixtures of diastereoisomers which have not been
separated. So far, we have not been able to isolate a
1:1-product from the reaction of 4c-Cl with TMeSt.29
When TMeSt (>2 equiv) was added to solutions of the
benzhydrylium tetrachloroborates (4a-c)-BCl4 in dichlo-
romethane, the absorbances of the benzhydrylium cat-
ions 4a-c+ disappeared, following the second-order rate
law given in eq 2.
Figure 1. Eyring plots for the reactions of 2,4,6-trimethyl-
styrene with the benzhydrylium ions 4a+, 4b+, and 4c+ (in
CH2Cl2).
-d[4+]/dt ) k2[4+][TMeSt]
(2)
For the determination of the second-order rate constants
k2, the previously described methods were em-
ployed.23,30,31 Because previous work has shown that free
and paired carbocations exhibit almost the same reac-
tivities,30 the degree of ion-pairing is not taken into
account.
From the temperature dependence of the second-order
rate constants (Figure 1), the Eyring activation param-
eters ∆Hq and ∆Sq were obtained as listed in Table 1.
As previously found for analogous reaction series,23
variation of the para-substituents of the benzhydrylium
ions affected ∆Hq whereas ∆Sq remained almost con-
stant (-117 ( 7 J mol-1 K-1).
A plot of log k20 °C vs the electrophilicity parameters
E of the benzhydrylium ions (Figure 2) yields the
nucleophilicity parameter N ) 0.68 and the slope
Figure 2. Linear free enthalpy relationships for the reactions
of ring-substituted styrenes with benzhydrylium ions 4+ (in
CH2Cl2). Rate constants are from Table 1 and ref 23.

Macromolecules, Vol. 38, No. 1, 2005
Cationic Polymerization of 2,4,6-Trimethylstyrene 35
Scheme 2. Synthesis of 1-Chloro-1,3-dimesitylbutane
(7-Cl)
Scheme 3. Lewis Acid Induced Reactions of 6-Cl and
7-Cl with 2-Chloropropene (-78 °C, CH2Cl2)
from coplanarity between the vinylic double bond and
the aromatic ring.
Electrophilic Reactivity of the
2,4,6-Trimethylstyryl Cation
The 2,4,6-trimethylstyryl cation 6+ and its addition
product to 2,4,6-trimethylstyrene (7+) were considered
as model systems for the propagating species in tri-
methylstyrene polymerization.
either 6-Cl or 7-Cl were treated with Lewis acids in
dichloromethane at -78 °C.
Addition of >3 equiv of 2-chloropropene to solutions
of 6-GaCl4 or 7-GaCl4 (usually in the presence of Et3-
BnN+ GaCl4- to avoid multiple addition) led to a decay
of the carbocation absorbances. From the time depen-
dence of the UV-vis absorptions, the second-order rate
constants were derived following the procedure de-
scribed in ref 31. Kinetic experiments at variable
temperature gave rise to the Eyring plots shown in
Figure 4. The unusually large scatter of the individual
points around the correlation lines in Figure 4 is due
to the low stability of the addition products 8 and 9
under the conditions of the kinetic experiments, as
recognized by the slow development of an UV-absorption
at λ ≈ 330 nm after the completion of the addition
reaction.
More important than the activation parameters given
in Table 2, which have a high uncertainty, are the
similar values of the rate constants observed for the
reactions of both 6+ and 7+ with 2-chloropropene. At
-67 °C, the cation 7+ reacts only 2.4 times faster with
2-chloropropene than 6+, which reduces to a factor of
1.4 at 20 °C (Table 2). Thus, the additional mesityl
Compound 7-Cl, the precursor of cation 7+, was
obtained by ZnCl2‚OEt2-catalyzed addition of trimeth-
ylstyryl chloride 6-Cl to TMeSt as shown in Scheme 2.
Recrystallization of the initially produced mixture of
diastereoisomers of 7-Cl yielded a single diastereomer,
the configuration of which was not determined.
Addition of 6-Cl or 7-Cl to solutions of excess GaCl3
in dichloromethane at -70 °C gives rise to the formation
of the carbocations 6+ and 7+, respectively, which show
similar UV-vis spectra (Figure 3). Since the same UV-
vis spectrum for 6+ was observed when the correspond-
ing bromo compound 6-Br [) 1-bromo-1-(2,4,6-trimeth-
ylphenyl)ethane] was treated with GaCl3, the species
responsible for the UV-vis spectra depicted in Figure
3 must not contain halogen.
To determine the electrophilic reactivities of 6+ and
7+, the rates of their reactions with 2-chloropropene, a
reference nucleophile,23 were determined. As shown in
Scheme 3, good yields of the 1:1-addition products 8 and
9 were obtained, when mixtures of 2-chloropropene with
Figure 3. UV-vis spectra of the tetrachlorogallate salts of cations 6+ and 7+ (generated at -70 °C by adding 6-Cl or 7-Cl,
respectively, to dichloromethane solutions of excess GaCl3).

36 Mayr et al.
Macromolecules, Vol. 38, No. 1, 2005
Scheme 4. Competition of the in Situ Generated
Carbocation 6+ with the Nucleophiles
Tributyl(2-methylallyl)stannane (10) and
Allyltrimethylsilane (12) in Dichloromethane at -78
°C
Figure 4. Eyring plots for the reactions of 2-chloropropene
with the carbocations 6+ and 7+ (in CH2Cl2).
Table 2. Eyring Activation Parameters of the Reactions
of 6-GaCl4 and 7-GaCl4 with 2-Chloropropene in
Dichloromethane
Scheme 5
electrophile ∆Hq/kJ mol-1 ∆Sq/J mol-1 K-1 k2(20 °C)/M-1 s-1
6+
24.6 ( 1.4
21.6 ( 1.9
-94.1 ( 6.2
-101 ( 8.6
(3.05 ( 0.51) × 103
7+
(4.37 ( 1.14) × 103
group in 7+ does not have a significant influence on the
electrophilicity of the carbocation. Substitution of N )
-3.46 and s ) 1.35 for 2-chloropropene23 and log k20 °C
for its reactions with the carbocations 6+ and 7+ into
eq 1 yields the electrophilicity parameters E(6+) ) 6.04
and E(7+) ) 6.16 for the carbocations. The magnitude
of the E parameters thus determined was confirmed by
the competition experiment described in Scheme 4.
Treatment of 6-Cl with ZnCl2‚OEt2 in the presence
of a mixture of tributyl(2-methylallyl)stannane (10) and
allyltrimethylsilane (12) gave rise to the formation of
the 4-mesityl-pent-1-enes 11 and 13, respectively. From
a series of experiments with variable concentrations of
10 and 12 (see Experimental Section) a competition
constant κ ) k10/k12 ) 24.7 ( 2.7 was obtained.32 Even
if the E value for 6+ determined above was wrong by 2
orders of magnitude, the high nucleophilicity of 10 (N
) 7.48, s ) 0.89)23 implies that the reaction of 6+ with
10 must be diffusion-controlled; that is, k10 ≈ 3 × 109
M-1 s-1. Combination with the competition constant κ
) 24.7 yields a rate constant of k12 ≈ 1.2 × 108 M-1 s-1
for the reaction of 6+ with allyltrimethylsilane (12).
Because reactions of such high rate do not have an
activation enthalpy,33 the value of k12 can be considered
to be independent of temperature. Substitution of k12
) 1.2 × 108 M-1 s-1, N(12) ) 1.79,23 and s(12) ) 0.9423
into eq 1 now gives an electrophilicity parameter E(6+)
) 6.79, in fair agreement with that derived from direct
rate measurements with 2-chloropropene, which con-
firms the reliability of E determined for the trimethyl-
styryl cation 6+.
steric effects.17,19,22,24,27 The propagation rate constant
kp calculated by eq 1 should, therefore, be considered
as an upper limit.
The isolation of the 1:1 adducts 8 and 9 as described
in Scheme 3 indicates that reionization of the 2-chlo-
ropropene adducts is difficult, even in the presence of
strong Lewis acids. For that reason, 2-chloropropene
may be used as a capping agent, particularly when the
weaker Lewis acid BCl3 is employed, as described in the
following article.16 Because carbocation 7+ resembles the
propagating species in trimethylstyrene polymerization,
the rate constant for the reaction of 7+ with 2-chloro-
propene determined in this work can be assumed to
reflect the rate of the capping reaction. The following
article16 shows how these data can be used for the direct
determination of kp in Scheme 5.
Experimental Section
General Data. 1H (300 MHz) and 13C NMR (75.5 MHz)
spectra of solutions in CDCl3 were obtained on a Bruker ARX
300 instrument and calibrated to tetramethylsilane as internal
standard (δH 0.00) or to the solvent signal (δC 77.0), respec-
tively. DEPT-135 experiments were used to obtain information
about the multiplicities of 13C resonances. Mass spectra were
obtained with a Finnigan MAT 95Q.
All reactions were performed in carefully dried glassware
under an atmosphere of dry nitrogen.
TMeSt is commercially available but was obtained in this
work from a synthetic sequence15,34,35 which starts with a AlCl3
promoted acylation of mesitylene by acetyl chloride (83%).
Reduction of the resulting ketone with lithium aluminum
hydride yielded alcohol 6-OH (74%) which was subsequently
converted into chloride 6-Cl by reaction with thionyl chloride
(98%). Potassium tert-butoxide induced HCl elimination gave
access to TMeSt (77%).
Propagation Rate Constant
If carbocation 7+ is accepted as a model for the
propagating cation in trimethylstyrene polymerization,
the propagation step can be approximated by the
reaction in Scheme 5.
When the reactivity parameters for 7+ and 2,4,6-
trimethylstyrene, summarized in Scheme 5, are substi-
tuted into eq 1, a rate constant of kp(20 °C) ) 3 × 107
M-1 s-1 is calculated, which is considerably higher than
that derived in the following paper.16 It has to be
regarded, however, that Scheme 5 describes the com-
bination of a bulky electrophile with a sterically hin-
dered nucleophile, and it has previously been demon-
strated that rate constants of such reactions are
overestimated by eq 1, which does not specifically treat
Dichloromethane solutions of the ZnCl2‚OEt2 complex were
prepared according to ref. 36.
2-(1-Chloro-3-(4-methoxyphenyl)-3-phenylpropyl)-1,3,5-
trimethylbenzene (5a). A mixture of the benzhydryl chloride
4a-Cl (232 mg, 1.00 mmol) and benzyltriethylammonium
chloride (455 mg, 2.00 mmol) in CH2Cl2 (50 mL) was cooled to
0 °C. The ZnCl2‚OEt2 complex (1.0 mL of a 3.9 M solution in
CH2Cl2) and TMeSt (146 mg, 1.00 mmol) were successively
added to the stirred and cooled solution. After 45 min, the
reaction mixture was hydrolyzed by the addition of a mixture
of concentrated ammonia and water (1/1, 20 mL). After the

Macromolecules, Vol. 38, No. 1, 2005
Cationic Polymerization of 2,4,6-Trimethylstyrene 37
separation of the phases, the aqueous layer was extracted with
diethyl ether (2 × 20 mL). The combined organic layers were
dried (MgSO4), and the solvent was evaporated under reduced
pressure. Purification of the crude product by column chro-
matography (silica gel, eluent: hexane/diethyl ether ) 10:1)
yielded 5a (330 mg, 87%) as a colorless oil. MS (70 eV), m/z
(%): 380 (7), 378 (M+, 19), 342 (14), 198 (14), 197 (100). During
the attempt to crystallize the chloride 5a from methanol, 5a
was completely converted into the corresponding methyl ether
5a′.
1-Chloro-1,3-bis(2,4,6-trimethylphenyl)butane (7-Cl). A
solution of 6-Cl (913 mg, 5.00 mmol) in CH2Cl2 (45 mL) was
cooled to -78 °C. Then dichloromethane solutions of ZnCl2‚
OEt2 (1.50 mL of a 3.9 M solution in CH2Cl2, 5.9 mmol) and
TMeSt (731 mg, 5.00 mmol in 5 mL CH2Cl2) were slowly added
and stirring was continued for 60 min at -78 °C. The reaction
mixture was hydrolyzed by addition of a mixture of concen-
trated ammonia and saturated aqueous ammonium chloride
(1/1, 20 mL). Then the aqueous layer was separated and
extracted with diethyl ether (2 × 20 mL). The combined
organic layers were dried (MgSO4), and the solvent was
removed under reduced pressure. The residue was purified by
filtration through a short column of neutral alumina (activity
I, eluent: hexane/diethyl ether ) 20:1). Recrystallization from
pentane yielded a single diastereomer of 7-Cl (320 mg, 20%)
as colorless crystals.
Because of hindered rotations and the formation of a
mixture of diastereomers, we were not able to assign all NMR
1
signals unambiguously. H NMR (300 MHz, CDCl3): δ 1.70,
1.72 (2 s, 3 H, CH3), 2.20, 2.55 (2 s, 2 × 3 H, 2 × CH3), 2.65-
2.77, 2.99-3.10 (2 m, 2 × 1 H, 2-H), 3.67, 3.68, 3.69 (3 s, 6 H,
OCH3), 4.05-4.13 (m, 1 H, Ar2CH), 5.15-5.24 (m, 1 H, 1-H),
6.77-7.36 (m, 11 H, ArH). 13C NMR (75.5 MHz, CDCl3): δ
19.7/19.8, 20.7, 21.1 (4 q, CH3), 43.0/43.2 (2 t, C-2), 47.9 (q,
1-OCH3), 55.1 (q, OCH3), 57.9/58.0 (2 d, Ar2CH), 79.4 (d, C-1),
113.7/113.8, 114.0/114.1 (4 s, Ar), 126.4, 126.5, 127.0, 127.1,
127.2, 127.3, 127.6, 127.8, 128.3, 128.5, 128.6, 128.7, 128.9,
129.1, 131.5 (d, Ar), 133.8, 134.3, 135.6, 137.6, 142.7, 144.0,
158.3, 159.0 (8 s, Ar).
1H NMR (300 MHz, CDCl3): δ 1.28 (d, J ) 7.4 Hz, 3 H,
4-H), 1.77, 1.78, 2.22, 2.23, 2.39, 2.54 (6 s, 6 × 3 H, 6 × CH3),
2.59-2.84 (m, 2 H, 2-H), 3.13-3.25 (m, 1 H, 3-H), 5.24 (t, J )
8.2 Hz, 1 H, 1-H), 6.71-6.82 (m, 4 H, ArH). 13C NMR (75.5
MHz, CDCl3): δ 18.8, 19.8, 20.6, 20.8, 21.1, 21.5 (6 q, CH3),
32.6 (d, C-3), 42.2 (t, C-2), 58.5 (d, C-1), 129.2, 129.3, 131.0,
131.4 (4 d, Ar), 133.3, 135.3, 136.0, 136.8, 137.1, 137.7, 137.86,
137.94 (8 s, Ar). MS (EI, 70 eV), m/z (%): 330 (11), 328 (M+,
34), 277 (12), 148 (12), 147 (100).
2-(3,3-Dichloro-1-methyl-butyl)-1,3,5-trimethylben-
zene (8). A solution of titanium tetrachloride (1.50 mL of a
0.89 M solution in CH2Cl2, 1.33 mmol) in CH2Cl2 (20 mL) was
cooled to -78 °C. After the dropwise addition of a solution of
6-Cl (183 mg, 1.00 mmol) and 2-chloropropene (153 mg, 2.00
mmol) in CH2Cl2 (5 mL), stirring was continued for another 4
h at -78 °C. The reaction mixture was then hydrolyzed by
the addition of a mixture of concentrated ammonia and
saturated aqueous ammonium chloride (1/1, 50 mL). After the
separation of the phases, the aqueous layer was extracted with
diethyl ether (2 × 20 mL). The combined organic layers were
dried (MgSO4), and the solvent was evaporated under reduced
pressure. Purification of the crude product by column chro-
matography (silica gel, eluent: hexane/diethyl ether ) 10:1)
yielded 8 (200 mg, 77%) as a yellowish oil.
2-(1-Chloro-3-(4-methoxyphenyl)-3-(4-tolyl)propyl)-1,3,5-
trimethylbenzene (5b). A mixture of the benzhydryl chloride
4b-Cl (246 mg, 1.00 mmol) and benzyltriethylammonium
chloride (455 mg, 2.00 mmol) in CH2Cl2 (50 mL) was cooled to
0 °C. The ZnCl2‚OEt2 complex (1.0 mL of a 3.9 M solution in
CH2Cl2) and TMeSt (292 mg, 2.00 mmol) were successively
added to the stirred and cooled solution. After 2.5 h, the
reaction mixture was hydrolyzed by the addition of a mixture
of concentrated ammonia and water (1/1, 20 mL). After the
separation of the phases, the aqueous layer was extracted with
diethyl ether (2 × 20 mL). The combined organic layers were
dried (MgSO4), and the solvent was evaporated under reduced
pressure. Purification of the crude product by column chro-
matography (silica gel, eluent: hexane/diethyl ether ) 10:1)
yielded 5b (240 mg, 61%) as a colorless oil.
1H NMR (300 MHz, CDCl3): δ 1.41 (d, J ) 7.2 Hz, 3 H,
1′-CH3), 2.05, 2.21, 2.33, 2.40 (4 s, 4 × 3 H, 4 × CH3), 2.61
(ABX system with 2JAB ) 14.6 Hz, 3JAX ) 5.6 Hz, 1 H, 2′-H),
2
3
2.77 (ABX system with JAB ) 14.6 Hz, JAX ) 4.6 Hz, 1 H,
2′-H), 3.62-3.72 (m, 1 H, 1′-H), 6.80 (s, 2 H, ArH). 13C NMR
(75.5 MHz, CDCl3): δ 21.1, 21.6, 21.81, 21.84 (4 q, CH3), 32.8
(d, C-1′), 38.1 (q, C-4′), 56.4 (t, C-2′), 91.4 (s, C-3′), 129.8, 131.6
(2 d, Ar), 135.3, 135.4, 135.6, 140.2 (4 s, Ar).
2,2-Dichloro-4,6-bis(2,4,6-trimethylphenyl)heptane (9).
A solution of 7-Cl (330 mg, 1.00 mmol), 2-chloropropene (153
mg, 2.00 mmol), and benzyltriethylammonium chloride (455
mg, 2.00 mmol) in CH2Cl2 (50 mL) was cooled to -78 °C. Then
a solution of gallium trichloride (8.00 mL of a 0.29 M solution
in CH2Cl2, 2.32 mmol) was added and stirring was continued
for another 30 min at -78 °C. The reaction mixture was
hydrolyzed by the addition of a mixture of concentrated
ammonia and water (1/1, 20 mL). After the separation of the
phases, the aqueous layer was extracted with diethyl ether (2
× 20 mL). The combined organic layers were dried (MgSO4),
Because of hindered rotations and the formation of a
mixture of diastereomers, we were not able to assign all NMR
1
signals unambiguously. H NMR (300 MHz, CDCl3): δ 1.73,
1.74 (2 s, 3 H, CH3), 2.13, 2.27, 2.55 (3 s, 3 × 3 H, 3 × CH3),
2.67-2.73, 2.99-3.05 (2 m, 2 × 1 H, 2-H), 3.69 (s, 3 H, OCH3),
4.03-4.10 (m, 1 H, Ar2CH), 5.17-5.22 (m, 1 H, 1-H), 6.77-
7.16 (m, 10 H, ArH). 13C NMR (75.5 MHz, CDCl3): δ 19.9, 20.7,
20.91, 20.94, 21.1 (5q, CH3), 43.1 (t, C-2), 47.4 (d, Ar2CH), 55.1
(q, OCH3), 58.0 (d, C-1), 113.76, 113.80, 114.0, 114.1 (4 s, Ar),
127.5, 127.7, 128.4, 128.6, 128.7, 128.8, 129.0, 129.1, 129.2,
129.3, 129.7, 131.4 (d, Ar), 133.7/133.9, 135.8/135.9, 136.0,
137.6/137.8, 141.0/141.1, 158.1/158.2 (s, Ar). MS (EI, 70 eV),
m/z (%): 392 (M+, 16), 356 (11), 212 (21), 211 (100). Anal. Calcd
for C26H29ClO (392.97): C, 79.47; H, 7.44; Cl, 9.02. Found: C,
79.99; H, 7.68; Cl, 8.74.

38 Mayr et al.
Macromolecules, Vol. 38, No. 1, 2005
6.69-6.80 (m, 4 H, ArH). 13C NMR (75.5 MHz, CDCl3): δ 19.7,
20.1, 20.5, 20.9, 21.2, 21.6, 26.9 (7 q, 7 × CH3), 32.8, 36.9 (2 d,
C-4 and C-6), 38.0 (q, C-1), 40.7, 54.9 (2 t, C-3 and C-5), 90.9
(s, C-2), 129.3, 129.9, 130.8, 131.2 (4 d, Ar), 135.3, 135.6, 136.0,
136.2, 137.0, 137.6, 137.7, 138.8 (8 s, Ar).
Table 3. Kinetics of the Reactions of
2,4,6-Trimethylstyrene (TMeSt) with 4a+ (in CH2Cl2)
T/°C [4a-Cl]o/M
[BCl3]0/M [TMeSt]o/M convn/% k2/M-1 s-1
-70.0 9.18 × 10-5 3.68 × 10-2 6.68 × 10-4
-60.4 4.66 × 10-5 3.74 × 10-2 4.52 × 10-4
-50.8 6.76 × 10-5 3.61 × 10-2 5.25 × 10-4
-40.8 8.71 × 10-5 3.97 × 10-2 7.68 × 10-4
-31.1 4.91 × 10-5 3.28 × 10-2 3.97 × 10-4
88
63
76
89
83
1.45 × 101
2.68 × 101
4.87 × 101
8.34 × 101
1.33 × 102
2-(1,3-Dimethyl-but-3-enyl)-1,3,5-trimethylbenzene (11).
A dichloromethane solution of ZnCl2‚OEt2 (1.00 mL of a 3.9
M solution in CH2Cl2, 3.9 mmol) was further diluted with
CH2Cl2 (50 mL) and cooled to -78 °C. Subsequently, a mixture
of 6-Cl (327 mg, 1.79 mmol) and 10 (1.38 g, 4.00 mmol) in
CH2Cl2 (2 mL) was slowly added. After stirring at -78 °C for
another 2 h, the reaction mixture was hydrolyzed by adding a
mixture of concentrated ammonia and water (1/1). The organic
layer was separated, dried (MgSO4), and the solvent was
removed under reduced pressure. The crude product was
dissolved in a mixture of hexane and diethyl ether (4/1) and
purified by filtration through a short column filled with silica
gel which contained tetrabutylammonium fluoride. The solvent
was removed under reduced pressure to give 11 (330 mg, 91%)
as a colorless oil.
Table 4. Kinetics of the Reactions of
2,4,6-Trimethylstyrene (TMeSt) with 4b+ (in CH2Cl2)
T/°C [4b-Cl]o/M
[BCl3]0/M [TMeSt]o/M convn/% k2/M-1 s-1
-70.4 2.05 × 10-4 3.74 × 10-2 6.33 × 10-4
-70.1 1.55 × 10-4 3.85 × 10-2 9.76 × 10-4
-60.7 2.13 × 10-4 3.64 × 10-2 4.93 × 10-4
-50.9 1.50 × 10-4 3.42 × 10-2 5.79 × 10-4
-41.2 1.40 × 10-4 3.48 × 10-2 2.94 × 10-4
-31.1 1.25 × 10-4 3.42 × 10-2 4.05 × 10-4
-21.9 1.05 × 10-4 3.59 × 10-2 6.06 × 10-4
-21.5 9.71 × 10-5 3.31 × 10-2 2.81 × 10-4
31
90
32
86
70
50
40
87
1.51
1.55
3.28
6.06
1.15 × 101
2.16 × 101
3.61 × 101
3.67 × 101
and the solvent was evaporated under reduced pressure to give
9 (380 mg, 94%) as a yellowish oil.
1H NMR (300 MHz, CDCl3): δ 1.26 (d, J ) 7.5 Hz, 3 H,
1′-CH3), 1.69 (s, 3 H, 3′-CH3), 2.21-2.49 (m, 11 H), 3.31-3.41
(m, 1 H, 1′-H), 4.70-4.72 (m, 2 H, 4′-H), 6.79 (s, 2 H, ArH).
13C NMR (75.5 MHz, CDCl3): δ 18.4, 20.6, 21.5, 22.3 (4 q, CH3),
32.9 (d, C-1′), 43.8 (t, C-2′), 111.5 (t, C-4′), 129.2, 131.2 (2 br
d, Ar), 134.8 (s, Ar), 136.0 (br s, Ar), 140.2 (s, Ar), 144.8 (s,
C-3′). MS (EI, 70 eV), m/z (%): 202 (M+, 5), 148 (11), 147 (100).
1,3,5-Trimethyl-2-(1-methyl-but-3-enyl)benzene (13).
As described above for the preparation of 11, ZnCl2‚OEt2 (1.00
1H NMR (300 MHz, CDCl3): δ 1.22 (d, J ) 7.1 Hz, 3 H,
7-H), 1.63, 1.72, 1.94 (3 s, 3 × 3 H, 3 × CH3), 2.20 (s, 6 H, 2 ×
CH3), 2.38, 2.44 (2 s, 2 × 3 H, 2 × CH3), 2.51-2.75 (m, 4 H, 2
× CH2), 2.95-3.02 (m, 1 H, 6-H), 3.38-3.47 (m, 1 H, 4-H),
Table 5. Kinetics of the Reactions of 2,4,6-Trimethylstyrene (TMeSt) with 4c+ [Generated from 4c-Cl and Different Lewis
Acids (LA), in CH2Cl2]
T/°C
[4c-Cl]o/M
Lewis acid
[LA]0/M
[TMeSt]o/M
convn/%
k2/M-1 s-1
-69.3
-69.3
-58.9
-49.7
-49.0
-39.7
-39.5
-30.5
19.9
1.24 × 10-4
9.33 × 10-5
6.75 × 10-5
1.13 × 10-4
5.62 × 10-5
9.59 × 10-5
8.44 × 10-5
8.52 × 10-5
6.23 × 10-5
7.57 × 10-5
8.14 × 10-5
4.47 × 10-5
ZnCl2‚OEt2
BCl3
1.71 × 10-2
3.70 × 10-2
3.39 × 10-2
1.56 × 10-2
3.53 × 10-2
8.25 × 10-3
3.74 × 10-2
3.21 × 10-2
4.23 × 10-3
3.53 × 10-3
4.14 × 10-3
4.55 × 10-3
2.72 × 10-2
3.36 × 10-2
3.84 × 10-2
3.71 × 10-2
4.00 × 10-2
1.31 × 10-2
2.83 × 10-2
1.21 × 10-2
1.06 × 10-3
4.55 × 10-4
1.39 × 10-2
1.27 × 10-2
80
31
70
73
26
53
78
42
35
20
61
31
1.35 × 10-2
1.25 × 10-2
3.48 × 10-2
9.83 × 10-2
8.13 × 10-2
2.42 × 10-1
1.61 × 10-1
4.89 × 10-1
4.56
BCl3
ZnCl2‚OEt2
BCl3
ZnCl2‚OEt2
BCl3
BCl3
TMSOTf
TiCl4
TMSOTf
TMSOTf
19.9
5.71
20.0
20.0
3.87
5.91
Table 6. Kinetics of the Reactions of 2-Chloropropene (Nuc) with 6+ [Generated from 6-Cl and GaCl3 in the Presence of
Benzyltriethylammonium Chloride (TEBA), in CH2Cl2]
T/°C
[6-Cl]0/M
[GaCl3]0/M
[TEBA]0/M
[Nuc]0/M
convn/%
k2/M-1 s-1
-67.4
-55.7
-48.3
-41.3
-40.1
-30.5
-27.6
1.41 × 10-4 a
2.09 × 10-4
1.06 × 10-4
8.44 × 10-5
6.02 × 10-5
7.85 × 10-5
4.85 × 10-5
6.76 × 10-3
6.42 × 10-3
6.52 × 10-3
6.49 × 10-3
6.28 × 10-3
5.85 × 10-3
4.70 × 10-3
4.37 × 10-4
7.86 × 10-4
5.32 × 10-4
5.30 × 10-4
6.34 × 10-4
5.91 × 10-4
3.10 × 10-4
32
57
31
31
35
58
53
33.1
57.5
105
175
177
284
411
2.04 × 10-3
2.07 × 10-3
2.06 × 10-3
1.99 × 10-3
1.86 × 10-3
1.66 × 10-3
a Compound 6-Br was used as precursor of cation 6+.
Table 7. Kinetics of the Reactions of 2-Chloropropene (Nuc) with 7+ [Generated from 7-Cl and GaCl3 in the Presence of
Benzyltriethylammonium Chloride (TEBA), in CH2Cl2]
T/°C
[7-Cl]0/M
[GaCl3]0/M
[TEBA]0/M
[Nuc]0/M
convn/%
k2/M-1 s-1
-66.0
-58.3
-55.2
-45.2
-37.5
9.69 × 10-5
8.72 × 10-5
1.06 × 10-4
7.54 × 10-5
6.30 × 10-5
5.36 × 10-3
5.79 × 10-3
5.85 × 10-3
5.01 × 10-3
5.23 × 10-3
1.90 × 10-3
2.05 × 10-3
2.07 × 10-3
1.77 × 10-3
1.85 × 10-3
4.41 × 10-4
3.24 × 10-4
7.23 × 10-4
4.12 × 10-4
3.44 × 10-4
24
66
58
82
82
80.7
138
137
250
440

Macromolecules, Vol. 38, No. 1, 2005
Cationic Polymerization of 2,4,6-Trimethylstyrene 39
Table 8. Relative Reactivities of
Tributyl(2-methallyl)stannane (10) and
Acknowledgment. Financial support by the Deut-
sche Forschungsgemeinschaft is gratefully acknowl-
edged.
Allyltrimethylsilane (12) toward 6+ Generated from 6-Cl
and ZnCl2‚OEt2 (CH2Cl2, - 78 °C)
product ratio
References and Notes
n0(6-Cl)/mmol n0(10)/mmol n0(12)/mmol
[11]/[13]a
κ
(1) (a) Plesch, P. H. J. Polym. Sci., Part A: Polym. Chem. 2002,
40, 2537-2544. (b) Plesch, P. H. Macromolecules 2001, 34,
1143-1147. (c) Plesch, P. H. Prog. React. Kinet. 1993, 18,
1-62.
0.22
0.22
0.22
0.22
0.22
0.22
0.22
0.22
0.50
0.50
0.50
0.50
0.50
0.50
0.25
0.50
2.50
5.00
3.00
1.50
8.00
2.00
2.50
4.00
3.50
2.39
3.22
6.37
1.61
4.85
1.69
2.41
21.2
28.4
23.3
23.8
29.9
23.9
24.2
22.9
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(3) Roth, M.; Mayr, H. Macromolecules 1996, 29, 6104-6109.
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8290.
a Determined from the ratio of the GC peak areas.
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576.
(6) Schlaad, H.; Kwon, Y.; Sipos, L.; Faust, R.; Charleux, B.
mL of a 3.9 M solution in CH2Cl2, 3.9 mmol), 6-Cl (327 mg,
1.79 mmol), and 12 (457 mg, 4.00 mmol) reacted in CH2Cl2
(50 mL) at -78 °C to give a crude product which was dried in
the high vacuum to yield 13 (280 mg, 83%) as a yellowish oil.
Macromolecules 2000, 33, 8225-8232.
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1H NMR (300 MHz, CDCl3): δ 1.28 (d, J ) 7.2 Hz, 3 H,
1′-CH3), 2.21-2.54 (m, 11 H), 3.20-3.30 (m, 1 H, 1′-H), 4.89-
5.04 (m, 2 H, 4′-H), 5.64-5.78 (m, 1 H, 3′-H), 6.78 (s, 2 H,
ArH). 13C NMR (75.5 MHz, CDCl3): δ 18.6, 20.6, 21.6 (3 q,
CH3), 34.9 (d, C-1′), 39.8 (t, C-2′), 115.2 (t, C-4′), 129.1, 131.1
(2 br d, Ar), 134.8, 136.0 (2 s, Ar), 138.0 (d, C-3′), 139.5 (s, Ar).
MS (EI, 70 eV), m/z (%): 188 (M+, 1), 148 (11), 147 (100).
(13) Vairon, J.-P.; Moreau, M.; Charleux, B.; Cretol, A.; Faust, R.
Macromol. Symp. 2002, 183, 43-52.
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1169.
Kinetic Experiments. Because the reactions of the colored
carbenium ions 4a-c+ with TMeSt (Tables 3-5) or of 6+ and
(16) De, P.; Sipos, L.; Faust, R.; Moreau, M.; Charleux, B.; Vairon,
7
+ with 2-chloropropene (Tables 6 and 7) gave rise to colorless
J.-P. Macromolecules 2005, 38, 41-46.
products, the second-order rate constants k2 (M-1 s-1) could
be determined photometrically. The reactions of the benzhy-
drylium ions 4a-c+ with TMeSt were followed with a Scho¨lly
KGS III UV/vis photometer with band-pass filters by Corion
as described in ref 30. For the reactions of 6+ and 7+ with
2-chloropropene, UV-visible spectra in the range of 200-600
nm were collected as a function of time by the use of a J&M
TIDAS diode array spectrophotometer that was linked to a
Hellma 661.502-QX quartz Suprasil immersion probe (5 mm
light path) via fiber optic cables with standard SMA connec-
tors.31 Calibration curves, i.e., the correlation between absor-
bance and concentration of the carbocations, were obtained
by determination of the absorbance of solutions of 4a-4c+,
6+, and 7+ at different concentrations. The temperature of
solutions during all kinetic studies was maintained ((0.2 °C)
by using circulating bath cryostats (water-glycol bath for T
> -10 °C, ethanol bath for T < -10 °C) and monitored with
a thermocouple probe that was inserted into the reaction
mixture.
(17) Mayr, H.; Patz, M. Angew. Chem. 1994, 106, 990-1010;
Angew. Chem., Int. Ed. Engl. 1994, 33, 938-957.
(18) Mayr, H. In Cationic Polymerization: Mechanisms, Synthesis
and Applications; Matyjaszewski, K., Ed.; Marcel Dekker:
New York, 1996; pp 51-136.
(19) Mayr, H.; Roth, M.; Lang, G. In Cationic Polymerization,
Fundamentals and Applications; Faust, R., Shaffer, T. D.,
Eds.; ACS Symposium Series Vol. 665: Washington, DC,
1997; pp 25-40.
(20) Mayr, H.; Kuhn, O.; Gotta, M. F.; Patz, M. J. Phys. Org.
Chem. 1998, 11, 642-654.
(21) Mayr, H.; Patz, M.; Gotta, M. F.; Ofial, A. R. Pure Appl. Chem.
1998, 70, 1993-2000.
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Competition Experiments. Under an atmosphere of dry
nitrogen, a mixture of 6-Cl, 10, and 12 was dissolved in dry
CH2Cl2 (20 mL), a drop of 2,6-di-tert-butylpyridine was added,
and the solution was cooled to -78 °C. Subsequently, the
reaction was started by adding a 3.9 M solution of ZnCl2‚OEt2
(0.1 mL) in CH2Cl2. After being stirred at -78 °C for 60 min,
the reaction mixture was hydrolyzed with concentrated NH3/
water (5 mL, 1/1). The organic layer was separated, dried over
MgSO4, filtered, and analyzed by GC (Fisons GC 8100 with
FID, packed column SE 30, 2.5 m × 2 mm, temperature range
of 50-300 °C, heating-up rate of 10 °C min-1). Because of the
similarities of the products 11 and 13, the GC peak areas of
11 and 13 were directly taken as a measure for the product
ratios, which were then used for the calculation of the
competition constants32 κ ) k10/k12. Details of the individual
experiments are summarized in Table 8.
66-77.
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97-102; Angew. Chem., Int. Ed. 2002, 41, 91-95. (b) Bug,
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(29) Under analogous conditions as described for the formation
of 5a and 5b, hydrolyzed starting material (4c-OCH3) was

40 Mayr et al.
isolated in almost quantitative yield after the addition of
Macromolecules, Vol. 38, No. 1, 2005
(33) Patz, M.; Mayr, H.; Bartl, J.; Steenken, S. Angew. Chem.
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490-492.
methanol to a mixture of 4c-Cl, 2,4,6-trimethylstyrene
(TMeSt), and ZnCl2‚OEt2, possibly because the equilibrium
is on the reactant side in the absence of a large excess of
TMeSt.
(34) Charlton, J. C.; Hughes, E. D. J. Chem. Soc. 1954, 2939-
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(32) For the evaluation of the competition constant κ from the
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1949, 575-581.
MA048389O