Fluorine-containing diacylperoxides and use thereof

A novel fluorine-containing diacylperoxide of the formula: EQU [RO--CH.sub.2 CF.sub.2 CF.sub.2 O--.sub.n CH.sub.2 CF.sub.2 COO--.sub.2 (I) wherein R is a C.sub.1 -C.sub.10 hydrocarbon group or halogen-containing hydrocarbon group, and n is an integer of 0 to 3, which can initiate polymerization of an ethylenically unsaturated monomer at a relatively low temperature.

FIELD OF THE INVENTION 
The present invention relates to novel fluorine-containing diacylperoxides 
and use thereof, particularly as an polymerization initiator for 
ethylenically unsaturated monomers. 
BACKGROUND OF THE INVENTION 
Hitherto, many diacylperoxides have been synthesized and studied, and 
various diacylperoxides useful as initiators in the polymer industries are 
prepared and commercially available. 
The peroxide to be used as a polymerization initiator for a 
fluorine-containing monomer is generally required to have following 
characteristics: 
1. Since the fluorine-containing monomer usually has high reactivity, it is 
desirable to carry out their polymerization under milder condition, for 
example, at a low temperature. Accordingly, the peroxide is required to 
liberate an active radical at a low temperature. 
2. Since radicals of propagating fluorine-containing polymeric chains 
generated during polymerization are active, the peroxide desirably hardly 
proceeds or does not proceed side reactions such as chain transfer 
reaction. 
3. Peroxide residues bonded to the chain ends of the polymer molecules 
should be thermally stable. 
As the peroxides which satisfy the above requirements, there are 
fluorine-containing diacylperoxides such as 
EQU [Cl(CF.sub.2 CFCl).sub.n CF.sub.2 COO--.sub.2 (DLP) 
EQU [H(CF.sub.2 CF.sub.2).sub.n COO--.sub.2 (DHP) 
EQU [ClCF.sub.2 CF.sub.2 COO--.sub.2 (DIP) 
EQU [CF.sub.3 CF.sub.2 COO--.sub.2 (3P). 
However, these conventional fluorine-containing diacylperoxides are used at 
a polymerization temperature of 10.degree. to 40.degree. C. or higher to 
achieve a practical decomposition rate of the peroxide. 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide novel fluorine-containing 
diacylperoxides which can liberate free radicals at a comparatively low 
temperature. 
Another object of the present invention is to provide a polymer having a 
terminal group which is easily changed to a hydroxyl group to give a 
so-called telechelic polymer. 
Accordingly, the present invention provides a novel fluorine-containing 
diacylperoxide of the formula: 
EQU [RO--CH.sub.2 CF.sub.2 CF.sub.2 O--.sub.n CH.sub.2 CF.sub.2 COO--.sub.2 (I) 
wherein R is a C.sub.1 -C.sub.10 hydrocarbon group or halogen-containing 
hydrocarbon group, and n is an integer of 0 to 3. 
The present invention also relates to the use of the fluorine-containing 
diacylperoxide (I) as a polymerization initiator for an ethylenically 
unsaturated monomer. 
DETAILED DESCRIPTION OF THE INVENTION 
The fluorine-containing diacylperoxide (I) of the invention easily 
liberates a radical at a low temperature and effectively initiates the 
polymerization of the monomer. Surprisingly, to the polymer prepared by 
the use of the diacylperoxide (I) as the polymerization initiator, 
hydroxyl groups can be introduced at the polymer chain ends to give a 
telechelic polymer. Although many attempts have been made to produce 
telechelic polymers by the use of various polymerization initiators, a 
telechelic polymer having terminal hydroxyl groups has not been prepared. 
In the fluorine-containing diacylperoxide (I), R is usually a C.sub.1 
-C.sub.10 hydrocarbon group or halogen-containing hydrocarbon group and 
includes a saturated or unsaturated, substituted or unsubstituted, 
aliphatic or aromatic group. The substituent may be a lower alkyl group, a 
phenyl group and the like. Specific examples of the group R are methyl, 
ethyl, isomeric propyl, isomeric butyl, pentyl, allyl, phenyl, 
methylphenyl, triphenylmethyl, chloroethyl, chloropropyl, 
2,2,3,3-tetrafluoropropyl, 2,2,2-trifluoroethyl, and the like. 
Specific examples of the fluorine-containing diacylperoxide (I) are as 
follows: 
EQU (CH.sub.2 OCH.sub.2 CF.sub.2 COO--.sub.2 (Ia) 
EQU (CH.sub.3 OCH.sub.2 CF.sub.2 CF.sub.2 OCH.sub.2 CF.sub.2 COO--.sub.2 (Ib) 
EQU (CH.sub.3 CH.sub.2 OCH.sub.2 CF.sub.2 COO--.sub.2 (Ic) 
EQU (CH.sub.3 CH.sub.2 OCH.sub.2 CF.sub.2 CF.sub.2 OCH.sub.2 CF.sub.2 
COO--.sub.2 (Id) 
EQU [(CH.sub.3).sub.3 COCH.sub.2 CF.sub.2 COO--.sub.2 (Ie) 
EQU [(CH.sub.3).sub.3 COCH.sub.2 CF.sub.2 CF.sub.2 OCH.sub.2 CF.sub.2 
COO--.sub.2 (If) 
EQU (CF.sub.3 CH.sub.2 OCH.sub.2 CF.sub.2 COO--.sub.2 (Ig) 
EQU (CF.sub.3 CH.sub.2 OCH.sub.2 CF.sub.2 CF.sub.2 OCH.sub.2 CF.sub.2 
COO--.sub.2 (Ih) 
The novel fluorine-containing diacylperoxide (I) may be prepared by 
reacting an acyl halide of the formula: 
EQU RO--CH.sub.2 CF.sub.2 CF.sub.2 O--.sub.n CH.sub.2 CF.sub.2 COX (II) 
wherein R and n are the same as defined above and X is halogen such as 
fluorine, chlorine, bromine and iodine, with Na.sub.2 O.sub.2 in water and 
extracting the product with a suitable solvent. The solvent used is one 
insoluble in water. A fluorine-containing solvent (e.g. 
trichlorotrifluorethane, tetrachlorodifluoroethane, trichlorofluoromethane 
and the like) is preferably used, although a water-insoluble hydrocarbon 
type solvent (e.g. benzene, toluene, xylene, hexane, heptane, and the 
like) can be used. The reaction temperature is usually -20.degree. to 
0.degree. C. 
The fluorine-containing diacylperoxide (I) of the invention is useful as an 
initiator for polymerizing various ethylenically unsaturated monomers. 
Specific examples of the monomers are hydrocarbon monomers (e.g. ethylene, 
propylene, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl 
butyrate, acrylic acid, methacrylic acid, acrylate or methacrylate such as 
methyl acrylate or methacrylate, acrylamide, methacrylamide, 
acrylonitrile, acrolein, methyl vinyl ketone, methyl vinyl ether, ethyl 
vinyl ether, diethyl fumarate, styrene and the like) and fluorocarbon 
monomers (e.g. vinyl fluoride, vinylidene fluoride, trifluoroethylene, 
tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropene, 
per(fluoroalkyl vinyl ether) and the like). The monomer may be used alone 
or a mixture with at least one of other monomers. 
The polymerization of the ethylenically unsaturated monomer using the 
fluorine-containing diacylperoxide (I) of the invention as the initiator 
may be carried out under substantially the same condition as in a 
conventional polymerization of the monomer. The polymerization is usually 
initiated at a temperature of -10.degree. to +30.degree. C. and preferably 
carried out in a solvent. The solvent may be the same as those used in the 
conventional method. Particularly for polymerization of fluorohydrocarbon 
monomers, used is a fluorine-containing solvent which hardly suffers from 
chain transfer such as perfluorokerosene, octafluorodichlorobutane, 
1,1,2-trifluoro-1,2,2-trichloroethane, 
1,2-difluoro-1,1,2,2-tetrafluoroethane and the like. 
The fluorine-containing diacylperoxide (I) of the invention has a terminal 
ether group in the molecule, which is also contained as a terminal group 
in the polymer produced by the use of the diacylperoxide (I). The terminal 
ether group in the polymer is easily changed to the hydroxyl group by 
thermal treatment or acid treatment with an inorganic acid (e.g. 
hydrochloric acid, hydrobromic acid and the like) or an organic acid (e.g. 
trifluoroacetic acid and the like). Since the fluorine-containing 
diacylperoxide (I) of the invention contains fluorine atoms and can be 
decomposed at a comparatively low polymerization temperature as described 
above, the monomer is polymerized under comparatively mild conditions. 
Since it has a high activity, particularly for the fluorine-containing 
monomers, it can very effectively initiate the radical polymerization of 
said monomers. This is confirmed from the fact that the 
fluorine-containing diacyl peroxide (I) has a shorter half-life than the 
conventional peroxides. 
The present invention will be hereinafter explained further in detail by 
following examples.

EXAMPLE 1 
Production of [(CH.sub.3).sub.3 COCH.sub.2 CF.sub.2 COO--.sub.2 (Ie) 
To a solution of sodium chloride (10 g) in water (40 g) contained in a 
flask equipped with a stirrer cooled to -20.degree. C., Na.sub.2 O.sub.2 
(1.0 g) was added and then 
.alpha.,.alpha.-difluoro-.beta.-t-butoxypropionyl chloride (B.P. 
52.degree.-53.degree. C./30 mmHg) (5.0 g) was dropwise added with stirring 
at the same temperature. After the addition of the chloride, the reaction 
mixture was stirred at the same temperature for 30 minutes and then 
1,1,2-trichloro-1,2,2-trifluoroethane (5 ml) was added and stirred at the 
same temperature for 30 minutes. Thereafter, an organic layer (about 6 ml) 
containing the produced peroxide was recovered. Iodometric titration of 
the organic layer revealed that the concentration of the entitled peroxide 
was about 0.3 g/ml. 
EXAMPLE 2 
In the same manner as in Example 1 but using 5 time amount of each reagent, 
the same procedures were repeated to obtain a solution (30 ml) containing 
the peroxide (Ie) in a concentration of 0.29 g/ml. 
EXAMPLE 3 
The solution containing the peroxide (Ie) prepared in Example 2 (1 ml) was 
diluted with 1,1,2-trichloro-1,2,2-trifluoroethane (9 ml) and kept on a 
water bath at 20.degree. C. in a nitrogen atmosphere to decompose the 
peroxide (Ie). The half-life at 20.degree. C. was about 21 minutes. The 
half-life of the peroxide (Ie) measured at 10.degree. C. was about 108 
minutes. 
The activation energy of decomposition was calculated to be about 24.2 
Kcal/mol. 
For comparison, half-lives of the conventional peroxides at 20.degree. C. 
are as follows: 
DLP--385 minutes 
DHP--360 minutes 
DIP--1,066 minutes. 
EXAMPLE 4 
In a stainless steel made reactor, vinylidene fluoride (17.1 g), 
perfluoropropene (19.2 g) and the solution of the peroxide (Ie) prepared 
in Example 2 (2 ml) were changed and retracted at 20.degree. C. for 21 
hours during which the interior pressure dropped from 22 Kg/cm.sup.2 G to 
20 Kg/cm.sup.2 G. 
After the reaction, the unreacted monomers were distilled off to obtain a 
liquid polymer (3.5 g). The presence of t-butyl terminal groups was 
confirmed by NMR analysis. 
The molar ratio of vinylidene fluoride and perfluoropropene was 77.3/22.7 
according to IR and NMR analyses. The molecular weight was about 4,500 
according to GPC. 
EXAMPLE 5 
Introduction of terminal hydroxyl groups to the polymer 
A part of the polymer prepared in Example 4 was heated at 200.degree. C. 
for 3 hours. IR and NMR analyses revealed that about 80% of the t-butyl 
terminal groups were converted to the hydroxyl groups while the rest of 
them remained unchanged. 
EXAMPLE 6 
Introduction of terminal hydroxyl groups to the polymer 
A part of the polymer prepared in Example 4 was treated with 
trifluoroacetic acid overnight, washed with water and dried. IR and NMR 
analyses revealed that about 92% of the terminal t-butyl groups were 
converted to the hydroxyl groups. 
EXAMPLE 7 
Styrene monomer (2 ml) and the solution of the peroxide (Ie) prepared in 
Example 2 (1 ml) were charged in a glass ampoule, evacuated and reacted at 
a room temperature for 5 hours. 
After the reaction, the content in the ampoule was poured in methanol to 
precipitate a polymer. The molecular weight of the polymer was 3,080 
according to GPC. 
The polymer was treated in the same manner as in Example 6 to give 
polystyrene having the hydroxyl groups at the polymer chain ends, which 
was confirmed by NMR analysis.