Cryoozonolysis of some perfluoroolefins and use of perfluoro ozonides as polymerization initiators

Article abstract of DOI:10.1023/A:1014829924249

Low-temperature (77-280 K) ozonolysis of perfluoro-4-methyl-2-pentene and perfluoro-2,4-dimethyl-3-ethyl-2-pentene by direct contact with ozone in the absence of solvents and oxygen was studied. The resulting perfluoro ozonides can be used as initiators o

Full text of DOI:10.1023/A:1014829924249

Russian Journal of Applied Chemistry, Vol. 74, No. 10, 2001, pp. 1740 1743. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 10, 2001,
pp. 1688 1695.
Original Russian Text Copyright
2001 by Kiryukhin, Barkalov, Ismoilov.
MACROMOLECULAR CHEMISTRY
AND POLYMERIC MATERIALS
Cryoozonolysis of Some Perfluoroolefins
and Use of Perfluoro Ozonides as Polymerization Initiators
D. P. Kiryukhin, I. M. Barkalov, and I. L. Ismoilov
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, Russia
Received May 7, 2001
Abstract Low-temperature (77 280 K) ozonolysis of perfluoro-4-methyl-2-pentene and perfluoro-2,4-di-
methyl-3-ethyl-2-pentene by direct contact with ozone in the absence of solvents and oxygen was studied. The
resulting perfluoro ozonides can be used as initiators of low-temperature polymerization and copolymerization.
Low-temperature ozonolysis of tetrafluoroethylene
(TFE) and hexafluoropropylene (HFP) by direct con-
tact of the reactants in the absence of solvents and
oxygen was studied in [1 3]. At equimolar ratio of
ozone and perfluoroolefin, the corresponding ozon-
ides are formed at low temperatures (140 230 K) in
quantitative yield by addition of ozone across the
double bond. The resulting perfluoro ozonides are
stable up to 250 290 K and decompose at higher
temperatures, with TFE ozonide being more stable
than HFP ozonide. The decomposition products of
TFE and HFP ozonides in statu nascendi initiate poly-
merization of TFE [1, 2] and some other monomers
[3, 4].
gen mixture was condensed in a trap cooled with
liquid nitrogen. Then, we removed oxygen from the
solution of ozone in liquid oxygen by vacuum distilla-
tion at 77 K, and the remaining crystalline ozone was
additionally purified by sublimation.
The phase state of the systems and the kinetics of
low-temperature ozonolysis and polymerization were
studied calorimetrically [5]. Known amounts of a
fluoroolefin and ozone were condensed in a vacuum
at 77 K in special glass calorimetric cells and sealed.
The reaction was performed in a slowly warming-up
calorimeter, and the reaction course was monitored by
the heat release.
The IR spectra of the fluoroolefins and reaction
products were taken on a Specord IR-75 spectrometer
using standard cells.
In this work, we studied the mechanism of cryo-
chemical ozonolysis of perfluoro-4-methyl-2-pentene
(HFP dimer, DHFP) and perfluoro-2,4-dimethyl-3-
ethyl-2-pentene (HFP trimer, THFP) and examined
the possibility of using the resulting ozonides as poly-
merization initiators. Our experimental procedure,
including sample preparation, excluded the uncontrol-
lable explosion mode of the reaction and allowed
ozonolysis of DHFP and THFP to be studied in the
absence of solvents and oxygen at direct contact of
ozone and perfluoroolefin.
On cooling to 77 K, DHFP passes into a glassy
state. In the course of heating of such a sample, we ob-
serve in the calorimetric curve a characteristic change
in the heat capacity due to a transition from the glassy
state to a supercooled liquid (Tg 110 K), crystalliza-
tion of the supercooled liquid (exothermic peak at
120 140 K), and melting at 160 K (Fig. 1, curve 1).
The heat of melting of DHFP, determined calorimetri-
1
cally, is 11.8 0.5 kJ mol .
EXPERIMENTAL
On heating a sample containing equimolar amounts
of O3 and DHFP, an exothermic reaction is observed
starting from approximately 210 K (Fig. 1, curve 2).
The rate of cryoozonation (heat release) increases
with temperature, reaching a maximum at 240 250 K.
The total activation energy of the reaction in the range
DHFP and THFP were purified by double distilla-
tion (bp 323.2 and 383 K, respectively). Ozone was
generated by passing an oxygen stream through an
electric-discharge glass ozonizer equipped with exter-
nal and internal electrodes. The resulting ozone oxy-
1
210 240 K is 90 5 kJ mol . Upon further warming,
1070-4272/01/7410-1740 $25.00 2001 MAIK Nauka/Interperiodica

CRYOOZONOLYSIS OF SOME PERFLUOROOLEFINS
the ozonation rate decreases because of the exhaustion
1741
of the reactants. The thermal effect of DHFP ozona-
tion, determined from a series of calorimetric runs, is
1
505 5 kJ mol .
In the IR spectrum of the ozonolysis products, com-
pared with the initial DHFP, new bands appear at
1
1850 (Rf FC=O bond [6]) and 1100 cm (five-mem-
bered ring [7]).
These results suggest that, at low temperatures,
ozonolysis of DHFP follows, similarly to that of TFE
and HFP [1 3], the well-known three-stage Criegee
mechanism [8], yielding the corresponding carbonyl
compounds and DHFP ozonide. The primary reaction
product is the so-called molozonide (I). It is unstable
and rapidly decomposes to form a bipolar ion and a
carbonyl compound. These intermediates couple again
in another sequence, forming a more stable ozonide II:
Fig. 1. Calorimetric heating curve: ( H) heat release,
( ) time, and (T) temperature; the same for Fig. 2.
O
(1) DHFP, (2) system DHFP O (molar ratio 1 : 1),
3
O
O
CF3
CFCF CFCF3 + O3
CF3
CFCF CFCF3
CF3
(3) THFP, and (4) system THFP O (molar ratio 1 : 1).
3
is initiated owing to the formation of a very reactive
bipolar ion in the course of ozonide decomposition.
Although ozonide II can be stored for a long time
at room temperature, it initiates polymerization in the
range 240 300 K. If ozonide II formed by ozonolysis
of DHFP is heated to 330 K, it irreversibly decom-
poses into perfluoroacyl fluorides, and these stable
products do not initiate polymerization.
CF3
I
F
<295 K CF3
CF3 O O
O
+
CF CF
C=O
CF3
CF CF CF CF3
>295 K CF3 O O
CF3
II
>330 K
With increasing DHFP content in the initial sam-
ples (molar ratio DHFP : O3 > 1 : 1), the thermal
effect of ozonolysis in the temperature range 210
(CF3)2CFCF O CF3CF O
The theoretical calculation of the heat released in
1
1
270 K remains unchanged (about 505 kJ mol ). This
these three stages (kJ mol ) [9] gave 240 for the for-
fact shows that, in the indicated temperature range,
ozone molecules add across the double bond of DHFP
in a 1 : 1 ratio only.
mation of molozonide, 32 for the formation of the bi-
polar ion and carbonyl compound, 214 for the forma-
tion of the final ozonide, and 486 for the overall re-
action. The last value is nicely consistent with that
determined calorimetrically, 505 5 kJ mol , which
confirms the suggested mechanism of low-temperature
ozonolysis of DHFP.
Also, we examined the possibility of cryoozonolysis
of THFP. On cooling to 77 K, THFP fully turns into
a glassy state. The calorimetric curve of heating of
this compound shows only a characteristic change in
the heat capacity due to transition from the glassy state
to the liquid (Tg = 145 K; Fig. 1, curve 3). No addi-
tion of ozone across the C=C bond is observed. No
changes, compared with the case of pure THFP, are
observed in the calorimetric curve recorded during
warming of the system THFP ozone (Fig. 1, curve 4).
Thus, THFP does not react with ozone in the range
77 300 K. Apparently, additional (compared with
TFE, HFP, and DHFP) CF3 groups in the THFP mol-
ecule shield the double bond and prevent access of
ozone to this bond.
1
The resulting ozonide II is in dynamic equilibrium
with the bipolar ion and carbonyl compound. At low
temperatures (<300 K) the equilibrium is shifted
toward formation of II, but at higher temperatures
(325 335 K) this ozonide irreversibly decomposes into
perfluoroacyl fluorides (CF3)2CFCF=O and CF3CF=O.
This conclusion was confirmed in studies of polymer-
ization effectively initiated by the obtained perfluoro
ozonides.
DHFP ozonide initiates, similarly to TFE and HFP
ozonides, polymerization of a number of monomers,
e.g., TFE. As shown previously [1 4], polymerization
As already noted, ozonides of TFE, HFP, and
DHFP initiate polymerization of many monomers.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 10 2001

1742
KIRYUKHIN et al.
As polymerization initiator, it is very convenient
to use ozonide II, which is liquid at room tempera-
ture, is not dangerously explosive, and can be stored
for a long time. Polymerization can be initiated in two
ways: in slow cooling of the monomer and initiator
in the range 77 300 K and in mixing of the monomer
and initiator at constant temperature.
Figure 2 (curve 1) shows a calorimetric curve of
TFE heating in the presence of ozonide II. Ozonide
II was prepared by warming the system DHFP
O3 (molar ratio 2 : 1) from 77 K to room temperature.
Actually, ozonide II was taken as a mixture with un-
changed excess of DHFP. Then TFE was condensed
into the calorimetric cell at 77 K, and the sample was
slowly warmed. As seen from Fig. 2 (curve 1), after
thawing of TFE and a mixture of ozonide II with un-
changed DHFP (endothermic peaks in the range 140
200 K in the calorimetric heating curve), heat release
due to TFE polymerization is observed starting from
approximately 230 K. The polymerization rate reaches
a maximum at 275 K, and at 300 K the monomer is
completely converted (yield of the polymer 100%).
Fig. 2. Calorimetric heating curves. System ozonide II
TFE: (1) initial and (2) after TFE polymerization.
Polymerization of TFE can also be initiated under
similar conditions with ozonides of TFE and HFP
[1 3] and occurs in the range 240 300 K. In the case
when polymerization in the system TFE HFP is in-
itiated with HFP ozonide, a copolymer is formed,
with the HFP content reaching 25 wt % [4].
Fig. 3. Kinetic curves of TFE polymerization at different
initial pressures of the monomer: ( ) PTFE yield and
( ) time. p, mm Hg: (1) 250, (2) 500, and (3) 750 (295 K).
Polymerization of TFE is initiated with ozonide II
not only in the condensed phase on warming the sys-
tem from 77 K to room temperature, but also in the
gas phase at 295 K. Figure 3 shows kinetic curves
of TFE polymerization at various initial pressures of
the monomer. Experiments were performed in sealed
ampules containing definite amounts of ozonide II
and monomer. It is seen that, depending on the initial
pressure of TFE, the conversion is 40 80% in 5 h.
It should be noted that perfluoro ozonides as poly-
merization initiators for fluoromonomers have fun-
damentally important advantages over the previously
known initiators [10]. Ozonide II is not dangerously
explosive and is safe in storage. The use of perfluoro
ozonides allows polymerization of TFE under atmo-
spheric pressure at room temperature with acceptable
rate. Perfluoro ozonides enable, in principle, poly-
merization of fluoromonomers in the gas phase in
the continuous mode. The use of gaseous TFE under
normal pressure allows the process equipment to be
significantly simplified, and abandoning the use of
emulsions and water reduces the environmental im-
pact of the process.
Fig. 4. Kinetic curves of MMA polymerization at different
concentrations of the initiator (ozonide II): ( ) polymer
yield and ( ) time. C, mol %: (1) 2, (2) 2, and (3) 3 (295 K).
The polymerization initiated by fluoroolefin ozonides
and the resulting products are of interest themselves;
here, we only briefly discuss some features of the
process.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 10 2001

CRYOOZONOLYSIS OF SOME PERFLUOROOLEFINS
1743
We also examined the possibility of initiating poly-
merization of monomers containing no fluorine. Ozo-
nide II effectively initiates polymerization of liquid
methyl methacrylate (MMA) and acrylonitrile (AN)
at room temperature. Figure 4 shows kinetic curves
of MMA polymerization at room temperature and
various initial concentrations of ozonide II. The result-
ing polymer is insoluble in methyl ethyl ketone, which
is untypical of polymethyl methacrylate. A chemical
analysis showed incorporation of fluorine into the
macromolecule in amounts significantly exceeding the
content corresponding to addition of the initiator frag-
ment in the initiation stage. Presumably, in the course
of MMA polymerization, the decomposition products
of the initiator or perfluoro-4-methyl-2-pentene are
incorporated in the macromolecule. Preparation of
polymethyl methacrylate containing perfluoro groups
is also of practical interest.
(3) Polymerization of methyl methacrylate initi-
ated with ozonide yields a polymer containing per-
fluoro groups.
ACKNOWLEDGMENTS
The study was supported by the Russian Founda-
tion for Basic Research, project no. 00-03-32212.
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