Control of free-radical polymerization of 2,2,2-trifluoroethyl methacrylate (TEMA) by a substituted fluorinated tetraphenylethane-type INITER

Article abstract of DOI:10.1016/S0022-1139(00)00406-1

This paper deals with the free radical polymerization of 2,2,2-trifluoroethyl methacrylate (TEMA) initiated by a substituted fluorinated tetraphenylethane-type INITER. The synthesis of a new fluorinated substituted tetraphenylethane is described. This initiator, prepared from benzophenone and 3,3,3-(trifluoropropyl)chlorodimethylsilane behaves as an INITER when used to polymerize TEMA. In the first period of polymerization, telechelic oligomers are formed. They were isolated from the mixture and their structure was characterized by ¹H-NMR spectroscopy. By thermal cleavage at the bonds between the last monomer unit and the end groups from the initiator, these telechelic oligomers are effective initiators of further free-radical polymerization of ethylenic monomers, yielding block copolymers besides the respective homopolymer. Thus, in a second step, styrene was introduced into poly(TEMA) to produce block copolymers with a macroinitiator efficiency close to 85%.

Full text of DOI:10.1016/S0022-1139(00)00406-1

Journal of Fluorine Chemistry 108 (2001) 37±45
Control of free-radical polymerization of 2,2,2-tri¯uoroethyl
methacrylate (TEMA) by a substituted ¯uorinated
tetraphenylethane-type INITER
J. Roussela,*, B. Boutevinb
a
Á
Á
SICAP, 145 Av. des Freres Lumiere, 84700 SORGUES, France
bENSCM, Laboratory of Macromolecular Chemistry (UMR-CNRS 5076), 8 rue de l'Ecole Normale,
34296 MONTPELLIER Cedex 05, France
Received 13 October 2000; accepted 10 November 2000
Abstract
This paper deals with the free radical polymerization of 2,2,2-tri¯uoroethyl methacrylate (TEMA) initiated by a substituted ¯uorinated
tetraphenylethane-type INITER.
The synthesis of a new ¯uorinated substituted tetraphenylethane is described. This initiator, prepared from benzophenone and 3,3,3-
(tri¯uoropropyl)chlorodimethylsilane behaves as an INITER when used to polymerize TEMA. In the ®rst period of polymerization,
1
telechelic oligomers are formed. They were isolated from the mixture and their structure was characterized by H-NMR spectroscopy. By
thermal cleavage at the bonds between the last monomer unit and the end groups from the initiator, these telechelic oligomers are effective
initiators of further free-radical polymerization of ethylenic monomers, yielding block copolymers besides the respective homopolymer.
Thus, in a second step, styrene was introduced into poly(TEMA) to produce block copolymers with a macroinitiator ef®ciency close to
85%. # 2001 Elsevier Science B.V. All rights reserved.
Keywords: Polymerization; Fluorinated tetraphenylethanes; INITER; 2,2,2-Tri¯uoroethyl methacrylate; Telechelic oligomers; Copolymerization
1. Introduction
The use of such molecules as initiators has been mainly
described by Bledzki and Braun [1±15]. Thus, and contrary
to benzopinacol [16,17], when compounds of the type
1,1,2,2-tetraphenyl-1,2-dicyanoethane (NC±CPh2±CPh2±
CN, TPCE) or 1,1,2,2-tetraphenyl-1,2-diphenoxyethane
(Ph±O±CPh2±CPh2±O±Ph, TPPE) are used in the polymer-
ization of a-substituted monomers (methyl methacrylate,
butyl methacrylate, methacrylic acid, etc.), telechelic oli-
gomers are obtained. Under certain polymerization condi-
tions (temperature, etc.), the chain ends, constituted by the
last monomer unit and the primary radical formed from the
initiator, may split up into new radicals able to re-initiate a
further polymerization. But it should be mentioned that the
degree of polymerization of these oligomers is rather small
and therefore, blocks from these oligomers are relatively
short compared to the second block which is produced by
normal polymerization of the second monomer. The same
authors [1] have also demonstrated that, in the case of MMA
polymerization in the presence of TPPE, the oligomers
which are formed may be used as macroinitiators in the
radical MMA polymerization or also as initiators in unsa-
turated polyester resins [18]. Numerous systems have been
The most common form for initiator of radical polymer-
ization is a compound which acts as a thermal source of
radicals. Such initiators are able to form free-radicals either
by thermal decomposition or by activation via a redox
mechanism. Both organic peroxides (oxygen±oxygen bond
cleavage) and azo compounds (carbon±nitrogen bond clea-
vage) are potentially useful. However, there are also less
common compounds containing a carbon±carbon bond cap-
able of cleavage under heat action.
In contrast to hexaphenylethane, diaryl methyl radicals
formed from tetraphenylethanes can initiate a radical poly-
merization. As they are strongly stabilized, they are also
able, under certain conditions, to take part in a reversible
coupling reaction on certain propagating radicals and to
induce, thus, a certain control over the polymerization.
Using tetraphenylethanes as ``INITER'' gives access ®rst
to the synthesis of telechelic oligomers, then, to block
copolymers through insertion of a second monomer.
* Corresponding author. Tel.: ‡33-4-90-395-130.
0022-1139/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 0 0 ) 0 0 4 0 6 - 1

38
J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
studied. Let us mention the copolymer prepared from benzyl
methacrylate oligomers and styrene [6] or also the copoly-
mer obtained from tert-butyl methacrylate oligomers and
styrene [19]. A possible application for these oligomers
consists in their chemical modi®cation into methacrylic
acid oligomers [19,20].
This system may then be used for the preparation of block
copolymers where one block is amphiphilic (methacrylic
polyacid-b-PS copolymer). Moreover, for special purposes it
may be interesting to use polymers with thermosensitive C±
C bonds, e.g. for the investigation of the fragmentation
processes of polymer chains in solution or even in bulk [21].
2.2. CF3BP synthesis
An amount of 1.2 g (0.05 ml) of magnesium turnings were
placed in a 100 ml three-necked ¯ask, equipped with a
condenser with a nitrogen inlet, a dropping funnel and a
septum, 50 ml of freshly distilled THF were added. Then,
18.2 g (0.1 mol.) of benzophenone dissolved in 20 ml of
THF were added through the dropping funnel followed by
19.15 g (0.1 mol) of 3,3,3-(tri¯uoropropyl)chlorodimethyl-
silane and ®nally 5 ml of TMU were added by a syringe
through the septum. The reaction mixture rapidly changed
from colorless to yellow, then to purple and ®nally to green.
The green solution obtained was cooled and stirred at room
temperature for 14 h. The solvent was evaporated under
reduced pressure and 50 ml of chloroform were added. The
solution was ®ltered to eliminate magnesium salts and then
chloroform was evaporated. A yellow colored wax was
obtained. The ®nal product can be crystallized easily after
adding a small amount of absolute ethanol or hexane.
15.4 g of a ®ne white powder were obtained (M ˆ 676 g/
mole; yield 46%).
Â
Á
More recently, De Leon-Saenz et al. [22] have brie¯y
described the MMA polymerization initiated by 1,1,2,2-
tetraphenyl-1,2-bis(trimethylsiloxy)ethane (TPSE). In
agreement with the previous works performed, they
observed that the oligomers obtained at the beginning of
the polymerization were able to initiate a further polymer-
ization. Also, from such oligomers with Mn ˆ 7000 g=mole
they prepared
a PMMA±PS block copolymer with
Mn ˆ 44000 g=mole.
In 2000, the mechanism of chain growth in TPSE-induced
free radical polymerization of MMA and styrene was again
investigated by the same authors [23]. In the case of MMA,
the diphenylmethyl radicals generated by TPSE are found to
reversibly combine with the growing PMMA radicals. In the
case of styrene, the mechanism appears to be more complex:
chain growth seems to involve a degenerative transfer.
But, although several substituted tetraphenylethanes were
synthesized, no ¯uorinated homologue has been prepared
previously. Furthermore, the polymerization of a ¯uorinated
monomer with a tetraphenylethane-type-compound has
never been studied. Hence, our purpose is to study the
polymerization of the 2,2,2-tri¯uoroethyl methacrylate
(TEMA) initiated by a ¯uorinated tetraphenylethane-type
INITER (CF3BP).
ꢀ
1H-NMR (DMSO-d6): d ˆ 0:1 ppm [s, 6H, ±Si(CH3)2];
0.6 ppm [m, 2H, ±CH2±Si]; 1.9 ppm [m, 2H, ±CH2±CF3];
7 ppm [m, 10H, aromatic protons].
19F-NMR (CDCl3): d ˆ 74 ppm [s, 3F, ±CF3].
ꢀ
C
H
Theoretical (%)
Expected (%)
63.90
63.65
5.92
5.95
2.3. Polymerization of the TEMA (general example)
A degassed solution of 1 g of CF3BP, 10 g of TEMA and
20 g of toluene introduced in a 50 ml two-necked ¯ask
equipped with a magnetic stirrer, a condenser related to a
nitrogen inlet, and a septum, was stirred at 1008C for 2 h.
After cooling, the solution was precipitated in a large
volume of methanol. The ®ltrate was evaporated under
reduced pressure then dried under high vacuum until the
mass remained constant.
First, the synthesis of this new initiator is detailed and
the polymerization mechanism is described. Then a block
polymerization system CF3BP±TEMA precursor/styrene is
studied.
2. Experimental
2.4. Copolymerization
2.1. General comments
The same procedure was used for the synthesis of block
copolymer but in this case, the reaction mixture was com-
posed of CF3BP±TEMA macroinitiator described above and
styrene. The copolymerization was carried out at 1008C for
6 h. Cyclohexane was used to extract polystyrene from the
block copolymer.
Benzophenone (99%), magnesium (turnings, 98%), tetra-
methylurea (TMU, 99%) were purchased from Aldrich and
were used without further puri®cation. Tetrahydrofuran
(THF) was distilled over sodium and stored under an inert
atmosphere.
3,3,3-(Tri¯uoropropyl)chlorodimethylsilane
(99%,
FLUOROCHEM) was distilled and stored under an inert
atmosphere prior to use. TEMA (99%, ELF ATOCHEM)
was freshly distilled and stored at low temperature before
use.
2.5. Characterizations
The initiators were characterized by H- and 19F-NMR
spectroscopy. The letters s and m designate singlet and
1

J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
39
multiplet, respectively. The conversion of monomer into
polymer was determined by 1H-NMR. The different spectra
were registered at room temperature on a AC 200 BRUKER
apparatus, using CDCl3 and DMSO-d6 as solvents. The
number average molecular weights for the oligomers and
the polymers were measured by size exclusion chromato-
graphy (SEC). Chromatograms were recorded on a spectra-
physics apparatus equipped with a SP 8850 pump, a shodex
RE-61R1 differential refractometer, a SpectroMonitor 3100
(UV detector) and ``phenogel'' columns (105, 104, 103,
the relatively high concentration of primary radicals
which were present in the medium, formed from the
initiator.
In this step, only a very small fraction of the monomer
Ð the monomer conversion did not exceed 1% Ð was
involved in this reaction. So, the conversion rate
remained low and only short oligomers were produced
(Scheme 1).
Indeed, the initiation being slow and the primary
radicals being strongly stabilized by mesomerism,
numerous free radicals play the role of counter-radicals,
leaving very few opportunities to the chain to grow.
The duration of this step, which always occurs, is
directly proportional to the initial concentration in
initiator [CF3BP]0 as shown in Fig. 2.
Ê
500 A) thermostated at 308C. THF was used as the eluent
and the ¯ow rate was 0.8 ml/min. The calibration was
performed with PMMA standard samples except for the
copolymer TEMA±styrene (styrene standard samples used).
2. During the second step, after most of the radicals have
been consumed, the conversion rate increases rapidly.
This increase is mainly due to the decomposition of the
chain ends. Due to the low concentration of radicals in
the medium, the probability for a reversible coupling
between them and the growing chain becomes lower and
the trend to recombine two propagating species appears.
All the radicals (ꢀCF2OSi(Me)2(C2H4CF3)) formed
from the chain ends cleavage may recombine with a
propagating species and at the same time generate a new
``dormant'' species but they are also able to initiate new
polymer chains.
3. Results and discussion
3.1. Synthesis of the initiator 1
1,1,2,2-Tetraphenyl-1,2-(dimethyl-3,3,3-tri¯uoropropyl-
siloxy)ethane (CF3BP) 1 was prepared from benzophenone,
magnesium and 3,3,3-(tri¯uoropropyl)chlorodimethylsilane
according to the method brie¯y described in 1968 by
Calas et al. [24] and detailed more recently by Crivello
et al. [25].
Moreover, this last reaction is responsible of the
falling off of the polymerization controlled character as
Â
Á
De Leon-Saenz et al. have explained [22]. Actually if the
radicals are irreversibly consumed, they progressively
lose their role of counter-radicals propagating species.
Thus, the probability for the two growing species to
recombine increases significantly. This recombination
reaction is expressed by a curve log([M0]/[M]) versus
time which is no longer linear as previously observed for
the first step.
1
The H-spectrum of the initiator is given in Fig. 1.
The kinetics of dissociation of CF3BP have not been
studied. Nevertheless, in 1986, Crivello et al. [25] showed
that decomposition of these initiators is highly activated by
the nature of the hindering substituent. Those bis(silyl
pinacolates) derived from benzophenone show appreciable
dissociation to their respective ketyl radicals even at 30yC.
For example, TPSE has a rate constant for dissociation of
3.3. Telechelic oligomers synthesis
In order to isolate the oligomers at low conversion rate, a
fractionated precipitation was performed in absolute ethanol
104x10 6 s at 408C. Thus, we considered that CF3BP is
1
totally and immediately decomposed at 1008C.
from the crude reaction mixture at ‰CF3BPŠ ˆ 0:0586 M.
0
The H-NMR spectrum of the ®ltrate is given in Fig. 3.
1
3.2. Polymerization of the TEMA
In this spectrum, we can observe a good correlation
between the integrals of Si(CH3)2 groups (0.65 for 6H)
and these of the aromatic protons (1 for 10H).
An example of TEMA polymerization in the presence of
CF3BP at 1008C is given in Fig. 2. The conversion of
monomer into polymer was followed by H-NMR.
As could be expected, the curve of conversion versus time
is quite similar to that of the classical system MMA±TPSE
[6] where two successive steps occur.
Indeed, from the 1H-NMR spectrum of the ®ltrate, if one
considers that all these oligomers are telechelic, by compar-
ison of the integral of the multiplet at 0.20 ppm corre-
sponding to the methyl groups in the a position to the silicon
atoms (I proportional to 12H) and the multiplet at 4.5 ppm
corresponding to the methyl groups in the a position to
the ester function (P proportional to 2H), we can calculate
the molecular weight by NMR according to relations (1)
1
1. During the first, named ``oligomerization'' step, tele-
chelic oligomers were formed. This formation is due to

40
J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
Fig. 1. 1H-NMR (DMSO-d6) spectrum of CF3BP initiator.
and (2):
ization to yield block copolymers, a block polymerization of
the CF3BP±TEMA precursor previously described (Mn ˆ
18 000 g=mole) was performed with styrene at 1008C for
6 h.
Generally, the oligomers obtained with substituted tetra-
phenylethanes are effective macroinitiators of free-radical
polymerization [6,19,20].
Block copolymers can be easily prepared by adding a
monomer and optionally a solvent to the macroinitiator and
heating the mixture at a temperature suf®cient to achieve a
thermal cleavage of the chain ends constituted by the last
monomer unit and the primary radical coming from CF3BP.
However, the major drawback of these systems is the
presence, in addition to the copolymer, of the homopolymer
1
Mnꢁ H NMR† ˆ ‰168  ꢁDPn†
Š
cum:
‡ weight of the extremities
(1)
(2)
P=2
DPn ˆ
I=12
1
that is, Mn ꢁ H NMR† ˆ ‰168  104Š ‡ 676 ˆ 18148 g=
mole.
3.4. Block polymerization system
In order to con®rm in a chemical way that the oligomers
are telechelic and are able to re-initiate a further polymer-
Fig. 2. Kinetic behavior plot for the polymerization in solution of TEMA initiated by CF3BP at 1008C and at different initial concentrations
(‰TEMAŠ ˆ 1:9 M).
0

J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
41
Scheme 1. Polymerization mechanism of 2,2,2-trifluoroethyl methacrylate with CF3BP.
from the second monomer. The formation of this homo-
polymer corresponding to the second block is expected
because the primary radicals released by homolytic cleavage
from poly(TEMA) chain extremities are able to initiate
polymerization, beside their ability to combine with the
growing macroradicals.
In this paper, we chose to limit our investigation to a
monomer that undergoes primary termination only by radi-
cal coupling, such as styrene. Scheme 2 supplies a repre-
sentation of the block copolymerization with CF3BP±
TEMA macroinitiator and shows the different species which
can exist with the block copolymer.
During the thermolysis, the macroinitiator is fragmented
to give essentially macroradical species which either can
undergo termination by disproportionation (II, III) or com-
bination (IV) to lead to inert homopoly(TEMA) or which
can react with styrene to initiate block copolymerization.
Depending on the mode of termination of the growing
radical chains and the ability of the primary radicals to play
the role of counter-radicals, A±B block copolymers and A±
B±A triblock copolymers may be produced.
Indeed, the possibility of generating chain ends that are
not functionalized by CF3BP fragments cannot be ruled out
because bimolecular termination does occur to a non-neg-
ligible extent.
Moreover, it is worthwhile to consider the energetic states
of the reactions described in Scheme 2. First, after thermal
decomposition of the macroinitiator, a high energy is
required to cause the addition of the stabilized primary
radicals to the monomer M. On the other hand, reaction
of these persistent radicals with the growing chains Mꢀ is
very fast, requiring little activation energy. Considerably
more energy is thus, required to cause fragmentation of the
M±I bonds to regenerate the original fragments.
In the case of styrene, this bond between the last monomer
unit and the primary radical from the initiator is stable at
classical temperatures. These species do not undergo further
fragmentation.
Consideration of these energies led to the suggestion that
the species
and
exist in the mixture.
So, according to Scheme 2, three different species can
coexist in the crude mixture: the inert homopoly(TEMA),

42
J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
Fig. 3. 1H-NMR (DMSO-d6) spectrum of trifluoroethyl methacrylate oligomers (‰CF3BPŠ ˆ 0:0586 M; T ˆ 1008C).
0
the homopolystyrene (thermal and initiated by the primary
radicals issued from the chain extremities) and the copoly-
mer (block and triblock copolymers).
In order to separate the homopolystyrene from the
methacrylic polymers (dead homopoly(TEMA) and the
copolymer), we have attempted to fractionate the mixture
using cyclohexane at 408C.
Polystyrene is soluble in cyclohexane (at temperature
above 358C), a good solvent for styrenic polymers but
not for methacrylic polymers. In this case, we have supposed
Scheme 2. Schematic representation of the copolymerization of CF3BP±TEMA macroinitiator with styrene. (I) CF3BP±TEMA macroinitiator; (II, III)
CF3BP±TEMA macroinitiator which undergoes termination by disproportionation; (IV) CF3BP±TEMA macroinitiator which undergoes termination by
radical coupling (for methacrylic monomers, these species can be neglected); (V, 2n): A±B±A triblock copolymers; (VI, n) A±B block copolymers; (VII, n)
PS telechelic oligomers; (VII, 2n): PS initiated by CF3BP radicals which undergoes bimolecular termination; (VIII, n): polymerization of thermal PS
controlled by CF3BP radicals; (IX, 2n): thermal PS which undergoes termination by radical coupling.

J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
43
Table 1
Synthesis of block copolymer from the radical polymerization of CF3BP±TEMAprecursor in the presence of styrene (T ˆ 100ꢂC, 6 h)
Amount of
styrene (g)
Amount of
macroinitiator (g)
Macroinitiator
Mn (g/mole)
Raw product composition (%)
Block copolymer
Mn (g/mole) (SEC)
Home PS
(filtrate)
Block copolymer
(precipitated)
10
5
1
1
18148
18148
25
32
75
68
56400
30500
that both the copolymers were not soluble in cyclohexane.
Under these same conditions, the macroinitiator was inso-
luble. Also, in the 1H-NMR spectrum of the ®ltrate, we can
only observe homopolystyrene with traces of Si(CH3)3
groups. The results are given in Table 1.
The percentage of the styrene in the block copolymer can
be easily determined from 1H-NMR (Fig. 5) using the
integrals of the multiplet situated at 4.3 ppm corresponding
to the ester protons from the TEMA block and the multiplet
at 6.2±7.2 ppm corresponding to the aromatic protons from
the styrene block. This value is close to 87%.
The SEC chromatograms of the CF3BP±TEMA precursor
and the puri®ed block copolymer (18 000/56 000) are given
in Fig. 4. The signal assigned to the precursor is shifted to
lower elution volumes, evidencing the formation of a block
copolymer. A copolymer of Mn ˆ 56 400 g=mole was
formed and no residual amount of precursor was detected.
However, as it is dif®cult to detect, by SEC, ¯uorinated
polymers which have a refractive index similar to the eluent
(THF), it may be possible that a low quantity of residual
macroinitiator has not been detected. As a result, this
quantity of dead homopoly(TEMA) has been neglected.
The same analytical technique was used with two differ-
ent detectors. Beside the usual refractive index detector, a
UV detector, set at 254 nm, was used to detect aromatic
groups in the polystyrene blocks. The response of the block
copolymer to these two detectors is identical, indicating that
the copolymer has an homogeneous composition. We can
conclude that the polymer is composed of covalently linked
blocks of PS and poly(TEMA).
By SEC, this percentage of styrene is about 70% (if we
consider that the molecular weight of the styrene block is
40 000 g/mole). This value can be explained by the approx-
imations made on the determination of the molecular weight
by SEC (PMMA and PS standard samples were used for the
calibration).
These experiments show that CF3BP is an ef®cient initia-
tor to synthesize block copolymers, demonstrating that the
®rst poly(TEMA) block was obtained in the conditions
corresponding to a controlled process.
3.5. Determination of the macroinitiator efficiency
In all cases, we can calculate the macroinitiator ef®ciency
(f) according to the relation (3):
% block copolymers
f ˆ
(3)
% block copolymers ‡ D
Fig. 4. Evolution of SEC curves during the block copolymerization: (a) TEMA precursor; (b) purified poly(TEMA)/polystyrene copolymers.

44
J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
Fig. 5. 1H-NMR (DMSO-d6) spectrum of the purified block copolymer.
Scheme 3. Mechanism of thermal autopolymerization of styrene in bulk.

J. Roussel, B. Boutevin / Journal of Fluorine Chemistry 108 (2001) 37±45
45
where D ˆ ‰% homopolystyrene obtainedŠ ‰% homopoly-
styrene thermally initiated ꢁspecies ꢁVIII; n† and ꢁIX; 2n† on
Scheme III-2†Š.
In the second step, these telechelic oligomers are effective
initiators for a further free radical polymerization. After
consumption of the primary radicals with increasing con-
version, normal propagation occurs. Telechelic oligomers,
isolated at low conversion, characterized by 1H-NMR, were
used to re-initiate the polymerization of styrene, yielding
block copolymers beside the homopolystyrene.
Fractionation of the crude copolymerization products in
cyclohexane at 408C allowed us to estimate the effective
quantity of copolymers and homopolystyrene, thermal and
initiated by the primary radicals. Thus, the ef®ciency of the
2,2,2-tri¯uoromethacrylate macroinitiator is close to 85%.
In fact, D represents the quantity of PS initiated by the
primary radicals formed from the macroinitiator chain
extremities (species (VII, n); (VII, 2n)).
However, in order to estimate the real quantity of thermal
PS, it is necessary ®rst to examine the autopolymerization
mechanism of styrene previously described by Mayo [26]
and Hamielec [27] (Scheme 3).
The reaction begins with a DIELS±ALDER cycloaddition
between two styrene molecules to produce 4 which
then undergoes a one electron transfer reaction with
another styrene molecule to form after proton transfer
the two benzylic radicals 5 and 6 noted (Iꢀ). Products 5
and 6 can combine to form 7 or add monomer to initiate
polymerization.
References
[1] A. Bledzki, D. Braun, Makromol. Chem. 182 (1981) 1047.
[2] A. Bledzki, H. Balard, D. Braun, Makromol. Chem. 182 (1981)
1057.
This mechanism can be summarized as:
monomer
monomer ‡ monomer ! Z ! radicals ꢁI†
According to Hamielec [27], the rate of thermal autopoly-
merization of styrene at 1008C is close to 2%/h. Thus, for a
reaction time of 6 h, we can write (copolymer 18 000/
56 000):
[3] H. Balard, A. Bledzki, D. Braun, Makromol. Chem. 182 (1981) 1063.
[4] A. Bledzki, H. Balard, D. Braun, Makromol. Chem. 182 (1981) 3195.
[5] A. Bledzki, D. Braun, W. Menzel, K. Titzschkau, Makromol. Chem.
184 (1983) 287.
‡
[6] A. Bledzki, D. Braun, K. Titzschkau, Makromol. Chem. 184 (1983)
745.
[7] A. Bledzki, D. Braun, H. Tretner, Makromol. Chem. 186 (1985)
2491.
75
75
[8] A. Bledzki, D. Braun, Makromol. Chem. 187 (1986) 2599.
[9] A. Bledzki, D. Braun, Polym. Bull. 16 (1) (1986) 19.
[10] A. Bledzki, D. Braun, K. Titzschkau, Makromol. Chem. 188 (1987)
2061.
f ˆ
ˆ
ˆ 0:85
75 ‡ f25 ꢁ6  2†g 88
This allows to conclude that at least 85% of the macro-
initiator has initiated the polymerization of styrene.
[11] A. Bledzki, H. Balard, D. Braun, Makromol. Chem. 189 (1988) 2807.
[12] D. Braun, H.J. Lindner, H. Tretner, Eur. Polym. J. 25 (1989) 725.
[13] D. Braun, Th. Skrzek, S. Steinhauer-Beiûer, H. Tretner, Macromol.
Chem. Phys. 196 (1995) 573.
4. Conclusion
[14] D. Braun, Th. Skrzek, Makromol. Chem. Phys. 196 (1995) 4039.
[15] D. Braun, S. Steinhauer-Beiûer, Eur. Polym. J. 33 (1997) 1.
[16] D. Braun, K.H. Becker, Makromol. Chem. 147 (1971) 91.
[17] D. Braun, K.H. Becker, Ind. Eng. Chem. Prod. Res. Develop. 10
(1971) 4.
1,1,2,2-Tetraphenyl-1,2-(dimethyl-3,3,3-tri¯uoropropyl-
siloxy)ethane was prepared from benzophenone and 3,3,3-
(tri¯uoropropyl)chlorodimethylsilane in 46% yield. This
new substituted ¯uorinated tetraphenylethane behaves as
a thermal ``INITER'' when used to polymerize 2,2,2-tri-
¯uoromethacrylate. The polymerization with this initiator is
characterized by two different stages; in the ®rst period,
telechelic oligomers from TEMA and primary radicals are
formed by radical termination:
Â
[18] A. Bledzki, W. Krolikowski, Kunststoffe 70 (9) (1980) 558.
[19] S. Steinhauer-Beiber, Angew. Makromol. Chem. 239 (1996) 43.
[20] D. Braun, Angew. Makromol. Chem. 223 (1994) 69.
[21] D. Braun, K.L. Kuhn, H. Meid, E.H. Hellmann, G.P. Hellmann, J.
Polym. Mater. 11 (1994) 197.
 Á
[22] M.E. De Leon-Saenz, Y. Gnanou, R. Guerrero, Polymer Preprints
(ACS) 38 (1) (1997) 667.
 Â
[23] E. De Leon-Saenz, G. Morales, R. Guerrero-Santos, Y. Gnanou,
Macromol. Chem. Phys. 201 (2000) 74.
[24] R. Calas, N. Duffaut, C. Biran, P. Bourgeois, F. Pisciotti, J.
Dunogues, C.R. Acad. Sci. Paris 267 (1968) 322.
[25] J.V. Crivello, D.A. Conlon, J.L. Lee, J. Polym. Sci. Part A. Polym.
Chem. 24 (1986) 1197.
[26] F.R. Mayo, J. Am. Chem. Soc. 90 (1968) 1289.
[27] A. Hamielec, A.W. Hui, J. Appl. Polym. Sci. 16 (1972) 749.