Copolymers of perfluorodioxoles

Details Copolymers of perfluorodioxoles Copolymers of perfluorodioxoles

1999-02-16

2002-01-01

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S209000, C526S242000, C526S255000

Reexamination Certificate

active

06335408

ABSTRACT:

The present invention relates to a class of dioxoles, and more specifically it relates to TFE copolymers with dioxoles, said copolymers having a higher Tg in the range 0.1-50% by moles of dioxole, in comparison with the copolymers of TFE with the known dioxoles.
Various structures of dioxoles have been described in the art. The U.S. Pat. No. 3,865,845 describes the perfluorodimethyldioxole (PDD) having the formula:
The patent EP 76,581 describes the following class of halo-perfluoroalkyl-dioxoles:
wherein Y
4
, Y
5
and Y
6
are F or Cl, while R
2
is a perfluoroalkyl radical having from 1 to 4 carbon atoms.
The patent EP 80,187 relates to 2,2,4,5-tetrafluoro-1,3-dioxole (PD) having the formula:
The patent EP. 633,257 relates to the following class of perfluoroalkyl-perfluoroalkoxy dioxoles having the formula:
wherein R
f
is a perfluoroalkyl radical having from 1 to 5 carbon atoms; X
1
and X
2
are, independently from each other, F or CF
3
.
The drawback of the perfluorodioxoles described in the U.S. Pat. 3,865,845, EP 80,187 and EP 76,581 is that they tend to spontaneously homopolimerize.
For example the perfluorodioxole (PD) of EP 80,187 tends to homopolymerize also at very low temperatures such as −78° C. Therefore this substance is not stable. A further drawback is that in the copolymerization products it is difficult to have an homogeneous distribution of the components along the chain.
In the GB patent 2,211,845 a process is described to obtain dioxoles having formula:
wherein R
1
and R
2
are independently selected from fluorine, chloroalkyl and C
1
-C
3
fluoroalkyl; R
3
is fluorine, or chlorine, or C
1
-C
3
perfluoroalkyl. In this patent reference is made to the U.S. Pat. 3,865,845 (see above) for the obtainment of dioxolanes from which the dioxoles having the above mentioned formula are obtained. This patent (GB 2,211,845) does not give any indication about the properties of the obtainable copolymers and in particular about the Tg.
In the art, the reactivity of substituted perfluoroalkyl dioxoles that is of perfluoro-2,2,4-trimethyl-1,3,-dioxole (PTD) (Ming-H. Hung, Macromolecules
26, 5829-5834, 1993
) having the formula
has been studied.
This compound is obtained by reacting hexafluoroacetone with 2,3 epoxy-1-propanol (M. H. Hung, J. Can. Chem. Soc. 1990, 112, 9672).
The PTD dioxole shows a poor reactivity: it lowers the polymerization kinetics, it does not homopolymerize and is not capable to copolymerize with TFE. The PTD low reactivity can be attributed to the steric effects of the 4 position trifluoromethyl group.
As regards the processes to obtain (per)fluorodioxoles, according to the art, the preparation of these compounds is carried out from the corresponding dioxolanes having a chlorine atom respectively in the 4 and 5 positions by dehalogenation reaction with metals such as Mg, Zn, in particular Mg. These reactions are carried out in organic solvent such as dioxane, DMF, in particular dimethylformamide (see U.S. Pat. No. 3,865,845, EP 76,581, EP 80,187). Reactions using polluting solvents are involved, whose disposal is difficult. In the art (WO 91/03472) it has moreover been shown that the dehalogenation yield increases when the dioxolane the anti isomer amount (the isomery is referred to the position of the two chlorine atoms in the molecule) is higher than that of the sin isomer.
The need was felt to obtain perfluorodioxoles allowing to prepare copolymers with olefinic comonomers, in particular TFE, having a Tg higher than the copolymers of the art with the same dioxole content.
A higher Tg value allows the use of the polymers at higher temperature.
It has been now surprisingly and unexpectedly found that it is possible to overcome this problem by means of a novel class of perfluorodioxoles, which are obtained with high yields by a new process more favourable to the environment than the known one.
An object of the present invention is a class of perfluoro-4-alkyl-1,3-dioxoles having the general formula:
wherein R
f
is a perfluoroalkylic radical having from 1 to 5 carbon atoms.
Surprisingly said class of dioxoles copolimerizes with olefinic monomers even if the perfluoroalkyl substituent is present in the 4 position of the ring, to the steric effects of which the PTD low reactivity has been attributed, as seen in the art.
In examining the prior art, it has been noticed that factors of steric type, due to the presence of groups directly bound to the carbon atoms in position 4 or 5 of the dioxolene ring, are capable to lessen or hinder the polymerization processes.
Surprisingly, the compounds of formula (I) are, on the contrary, capable to easily (co)polymerize.
The preferred compound in the general formula is perfluoro-4-methyl-1,3-dioxole (PMD) having the formula (II):
A further object of the present invention are the copolymers with monomers containing olefinic or of olefinic type unsaturations, obtainable with the compounds of formula (I), containing from 0.1 to 50% by moles of the following unit:
wherein R
f
is a perfluoroalkylic radical as above defined.
These polymers show a more homogeneous composition along the chain, also when the dioxoles concentration in the polymer is higher than 12% by moles.
The perfluorodioxoles of the invention can copolymerize with one or more comonomers having oelfinic unsaturations, such as for example, differently from PTD, tetrafluoroethylene.
It is surprising and unexpected that the copolymers with TFE in which the dioxole content of the invention is in the range 0.1-50% by moles have an improved Tg in comparison with the TFE copolymerized with the known dioxoles.
The monomers of the invention can copolymerize with vinyilidene fluoride, vinyl fluoride, trifluoroethylene, perfluoropropene, perfluoromethylvinylether, perfluoroethylvinylether, perfluorodioxole PD, perfluoro (2,2-dimethyl)-1,3-dioxole, perfluoro-4-methoxy-1,3-dioxole, CF
2
=CF—O—CF
2
—CF
2
—SO
2
F, CF
2
=CF—(OCF
2
(CF
3
) CF)
n
—O—CF
2
—CF
2
—SO
2
F wherein n is an integer from 1 to 3, chlorotrifluoroethylene, vinyl chloride, methyl (meth)acrylate, butyl (meth)acrylate, ethylene.
The copolymers can be prepared by polymerization of radical type, both in aqueous and organic medium.
In the aqueous medium polymerizations, the polymerization initiator can be any substance capable to produce radicals, such as for instance peroxides, persulphates or azo-compounds. These compounds in the reaction conditions have an average life such as to allow to obtain the polymer with the desired molecular weight. Also a reducing agent can optionally be used, such as for instance an iron salt, in order to promote the initiator decomposition.
The used initiator amount depends, as known, on the polymerization temperature, on the optional transfer agent presence, on the desired molecular weight and generally on the employed reaction conditions. The aqueous medium polymerization requires the presence of an emusifying agent. See for instance EP 184,459.
Alternatively, the polymerizations can be carried out in organic solvent as described in U.S. Pat. No. 3,642,742. Any initiator suitable to the TFE polymerization in organic solvent can be used. Preferably the initiator must be soluble in the reaction solvent. Examples of initiators are alkylpercarbonates, perfluoroacylperoxides, benzoyl peroxide and azo-bis(isobutyronitrile).
Redox systems can also be used such as those described in Prog.
Polym. Sci
, 8, 61 (1982). The solvent is generally selected from (hydro) (chloro) fluorocarbons and (hydro) perfluoropolyethers, when H is present it is in one or both ends, preferably in both.
The novel polymers have Tg higher than those of the polymers of the art containing the same dioxole percentage, as shown in Table 1.
As already said, higher Tg values allow a greater flexibility of the polymer use at high temperatures.
The TFE crystalline copolymers are used to prepare dielectric materials.
Amorphous copolymers containing the invention dioxoles are used for coating of electric wires and of parts to be insulated, besides in the optical fibers field, du

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