Oligomer preparation from hexane by radical polyaddition with bis(α-trifluoromethyl-β,β-difluorovinyl) terephthalate

Article abstract of DOI:10.1039/b406116k

Polymer preparation from hexane as a starting material by radical polyaddition with bis(α-trifluoromethyl-β,β-difluorovinyl) terephthalate [CF₂=C(CF₃)OCOC₆H ₄COO-C(CF₃)=CF₂] was investigate

Full text of DOI:10.1039/b406116k

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Oligomer preparation from hexane by radical polyaddition with
bis(a-trifluoromethyl-b,b-difluorovinyl) terephthalate{
Tadashi Narita,*a Hiroshi Hamanab and Satoshi Hattoria
a Department of Material Science and Engineering, Graduate School of Engineering, Saitma Institute of
Technology, 1690 Fusaiji, Okabe, Saitama 369-0293, Japan. E-mail: narita@sit.ac.jp
b Department of Applied Chemistry, Faculty of Engineering, Saitama Institute of Technology, 1690 Fusaiji,
Okabe, Saitama 369-0293, Japan
Received (in Cambridge, UK) 22nd April 2004, Accepted 21st July 2004
First published as an Advance Article on the web 7th September 2004
Polymer preparation from hexane as a starting material by
radical polyaddition with bis(a-trifluoromethyl-b,b-
reaction was found to be almost completed within 1 day. The
reaction scarcely took place in the lower feed amount of hexane.
The products were purified by treating the reaction system with a
silica gel column (eluent, hexane : chloroform ~ 9 : 1) in order to
remove benzoic acid formed by decomposition of BPO, and by
separating with size exclusion chromatography (SEC). The results
of GC analyses showed that two major products were obtained.
The results of mass spectra by chemical ionization method showed
the low-boiling material should be 1 : 1 addition product of BPFP
with hexane since the molecular ion peak was observed at m/z ~
338, and the high-boiling material 2 : 1 addition product since the
molecular ion peak was at m/z ~ 590. The structure of 2 : 1
addition product was determined by NMR measurements. The
absorption at 5.9 ppm in 1H NMR was assignable to the proton of
–CF2–CH(CF3)– and the peaks around 8 ppm are assigned to
phenyl protons. The absorptions of the hexane moiety appeared
from 0.7 to 2.6 ppm. These suggest that the compound is the
reaction product of BPFP with hexane. Assignment of the carbons
of methyl, methylene and methine were determined by the help of
the distortionless enhancement by polarization transfer (DEPT)
NMR measurement. The absorptions of trifluoromethyl and
difluoromethylene fluorines were measured at around 70 ppm and
from 2100 to 2120 ppm, respectively. The ratio of methyl,
methylene and methine of the hexane moiety in the addition
compound was about 1 : 1 : 1 which was calculated from the areas
difluorovinyl) terephthalate [CF2LC(CF3)OCOC6H4COO–
C(CF3)LCF2] was investigated to afford polymers bearing a
molecular weight of as high as 5.5
polyaddition mechanism including
mechanism was proposed.
6
103, and the
1,5-radical
shift
In previous work1 it has been demonstrated that the F-enol
benzoate, 2-benzoxypentafluoropropene [CF2LC(CF3)OCO–
C6H5] (BPFP),2 serves as a good and selective acceptor towards
nucleophilic radicals generated from cyclic ethers, alcohols, and the
tin hydride to afford the addition products which are potentially
useful for the preparations of a variety of functionalized
organofluorine compounds. The reaction was developed for the
preparation of polymer from bis(a-trifluoromethyl-b,b-difluorovi-
nyl) terephthalate [CF2LC(CF3)O–COC6H4COOC(CF3)LCF2]
(BFP) with 1,4-dioxane which was incorporated into the polymer
main chain (eqn. (1)).3 This led to the preparation of polymers
bearing diethyl ether, 1,2-dimethoxyethane, triethylamine or
glutaraldehyde moieties in the polymer main chain derived from
BFP with corresponding compounds.4 The results have pointed out
that polymers could be synthesized from bisperfluoroisopropenyl
esters with these compounds which have never been supposed to be
incorporated into polymer main chains.
1
of the corresponding H NMR peaks.
More detailed analysis on the di-addition product of BPFP with
hexane was carried out by the J-resolved NMR measurement. The
result is shown in Fig. 1. The methyl group whose absorptions are
measured from 0.8 to 1.0 ppm is concluded to be adjacent to the
methylene group since the splitting of the peaks is three, and the
other methyl group assigned to the peaks from 1.0 to 1.2 ppm is
The radicals derived from cyclic hydrocarbons such as
cylcopentane, cyclohexane and cycloheptane were also found to
achieve the addition reaction onto BPFP.5 The radical addition
might then be applicable to a variety of compounds which possess
carbon–hydrogen bonds. It was, however, unsuccessful to prepare
polymer from a-trifluoromethyl-b,b-difluorovinyl cyclohexanecar-
boxylate [CF2LC(CF3)OCOC6H11] by self-polyaddition (eqns. (2)
and (3)).
(2)
(3)
This paper is concerned with the preparation of polymers from
BFP with hexane which is a typical aliphatic hydrocarbon. In order
to investigate the polyaddition reaction conditions, the radical
addition of BPFP with hexane was carried out at 80 uC initiated by
benzoyl peroxide (BPO) for 1, 3, and 5 days reaction times at a feed
of BPFP to hexane of 1.0 to 10. The conversions of BPFP
measured by GC were 61.2%, 66.1% and 63.1%, respectively. The
{ Electronic supplementary information (ESI) available: Experimental
details. See http://www.rsc.org/suppdata/cc/b4/b406116k/
Fig. 1 J-resolved 1D NMR spectrum of 2 : 1 addition product of BPFP
with hexane.
2 3 4 0
C h e m . C o m m u n . , 2 0 0 4 , 2 3 4 0 – 2 3 4 1
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Table 1 Polyaddition of BFP with hexane
Hexane/
mmol
BPO ~
/mmol
Time/
days
Yieldb
(%)
Mw/
Mn
Mn 6 103
5
10
25
50
50
50
50
50
2
2
2
1
2
2
1
2
2
7
7
7
5
5
7
7
21
7
5
19
24
14
39
31
13
39
6
3.2
5.5
3.8
1.8
1.4
1.9
Scheme 1 Postulated addition reaction mechanism of BPFP with hexane.
4.3
3.7
1.3
1.9
100
assignable to the methine proton of the BFP moiety in the polymer
chain and the absorptions at about 8.0 ppm were assigned to
phenyl protons. The peaks assignable to the hexane moiety
appeared from 0.5 to 2.5 ppm. The polyaddition reaction is
concluded to take place at methylene carbons of hexane since the
absorptions around 1.0 ppm were assigned to methyl protons and
the peak at 2.1 ppm was assignable to methine protons of the
hexane moiety in the polymer main chain determined on the basis
of the results of the model reaction of BPFP with hexane as
described previously. The results of 19F NMR and 13C NMR
supported the conclusion. Therefore, the reaction is depicted as in
eqn. (4).
a BFP: 5.0 mmol; temp.: 80 uC. b After reprecipitation with CH3OH.
One of the reasons why the preparation of polymer from
CF2LC(CF3)OCOC6H11 failed is probably because of low
concentration of the cyclohexyl group compared to that of the
perfluoroisopropenyl group in combination with its restricted
structure of cyclohexyl group compared to aliphatic hydrocarbons
which might disturb the radical shift.
The 5% weight-loss temperature of the polymer derived from
BFP with hexane was about 279 uC measured by thermogravi-
metric analysis.
This might be the first example which gives the clear evidence
that an aliphatic hydrocarbon like hexane could be a starting
material to preparation of a polymer in one step reaction and could
perform as a bifunctional compound. Though aliphatic hydro-
carbons used to be named as sort of ‘‘paraffin’’ compounds which
means ‘‘hardly reactive’’, these results suggest that aliphatic
hydrocarbons might possibly be the starting materials for organic
syntheses and polymer preparation.
This work was financially supported in part by the Mazda
Foundation and the High-Tech Research Center Program of
Saitama Institute of Technology founded in 1999 by the support of
the Ministry of Education, Culture, Sports, Science and Technol-
ogy of Japan, to which the authors are grateful. Messrs. M. Sato,
N. Watanabe, Y. Yamashita, H. Nakano, J. Yoshida, and
S. Okubo are thanked for their experimental assistance.
Fig. 2 SEC of polyaddition product of BFP with hexane; (a) before
reprecipitation, (b) after reprecipitation with methanol.
adjacent to the methine group since the splitting is two. The
conclusion of the structural analyses of the product is shown in
Scheme 1. The product might be yielded by the addition of the
radical derived from the hydrogen-abstraction at the 2-position of
hexane to the a-carbon of BPFP followed by the 1,5-radical shift.
The hydrogen-abstraction from methylene carbon is reported to be
much easier compared to that from methyl carbon.6
Polyaddition of perfluoroisopropenyl esters with hexane was
investigated since polyaddition of a-trifluoromethyl-b,b-difluoro-
vinyl cyclohexanecarboxylate was unsuccessful though the radical
additions of BPFP with hydrocarbons such as cyclopentane,
cyclohexane and cycloheptane took place, as has been described
above.5 The results of polyaddition of BFP with hexane are
summarized in Table 1. Polymers of molecular weights of several
thousands are yielded under the reaction conditions examined here,
as expected based on the results of the model reaction mentioned
above. The yields, however, are low in the case of lower feed ratio
of hexane, and higher concentrations of BPO in feed are necessary
to obtain enough yields of polymers. The molecular weights of
polymers produced increase with increases in the amount of hexane
charged to the reaction system.
Notes and references
1 T. Narita, T. Hagiwara, H. Hamana, K. Tomooka, Y.-Z. Liu and
T. Nakai, Tetrahedron Lett., 1995, 36, 6091.
The typical SEC of the product of BFP with hexane is shown in
Fig. 2. The molecular weight distribution of the sample before
reprecipitation is multimodal. The polyaddition may then take
place with side reactions besides the reaction depicted in Scheme 1.
The higher molecular weight polymer can be separated by
reprecipitation with methanol, as shown by the solid line in
Fig. 2 which shows the unimodal molecular weight distribution.
The results of the polyaddition reactions showed that the gel
formation besides soluble polymer production took place in the
reaction systems of heptane and octane. Hexane works, therefore,
bifunctionally, and heptane and octane perform as bifunctional
and multifunctional compounds.
2 (a) C.-P. Qian and T. Nakai, Tetrahedron Lett., 1988, 29, 4119; (b)
C.-P. Qian, T. Nakai, D. A. Dixon and B. E. Smart, J. Am. Chem. Soc.,
1990, 112, 4602.
3 (a) T. Narita, T. Hagiwara, H. Hamana, K. Enomoto, Y. Yoshida and
Y. Inagaki, Macromol., Rapid Commun., 1998, 19, 485; (b) H. Fujiwara,
M. Iwasaki, T. Narita and H. Hamana, J. Fluorine Chem., in press
4 (a) T. Narita, T. Hagiwara and H. Hamana, Macromol. Chem. Phys.,
2000, 201, 220; (b) T. Narita, H. Hamana, M. Takeshita and
H. Nakagawa, J. Fluorine Chem., 2002, 117, 67; (c) T. Narita,
H. Hamana, M. Takeshita, K. Nishizawa and K. Kitamura,
J. Fluorine Chem., 2002, 117, 55.
5 T. Narita, T. Hagiwara, H. Hamana, K. Kitamura, Y. Inagaki and
Y. Yoshida, J. Fluorine Chem., 1999, 97, 263.
The structure of the polymer was determined by NMR
measurement. The peak around 6.0 ppm in 1H NMR was
6 J. Fossey, D. Lefort, and J. Sorba, Free Radicals in Organic Chemistry,
J. Wiley & Sons, New York, 1995, p. 213.
C h e m . C o m m u n . , 2 0 0 4 , 2 3 4 0 – 2 3 4 1
2 3 4 1