Synthesis and application of  -bromo-perfluoroalkylvinyl ethers
V.M.Andrushin, V.V.Drozdov
Report V. Study of physical and mechanical properties of
copolymers of fluoroolefins with -bromoperfluoroalkylvinyl
ethers.
1. Introduction
In report IV (1) the routes to modify fluoroplasts by copolymerization of
tetrafluoroethylene (TFE) and vinilydene fluoride (VDF) with bromo-perfluoroalkylvinyl
ethers (BrAVE) of the general formula of Br(CF2)nOCF=CF2 where n=2 (
BrAVE-2) and n=4 (BrAVE-4) have been described. The introduction of fluoroalkylvinyl
ethers to copolymerization with olefins is known to improve processibility of the
copolymers, increases their resistance to low temperatures and their stability in
aggressive chemical media.
They are used as the second and third copolymers (2-4)
In particular, a fluoroelastomer based on triple TFE copolymer, perfluoromethylvinyl ether
and substituted perfluoroalkylvinyl ether of the general formula of CF2=CFORfX
is known.
Bromine-containing molecules allow to synthesize new types of fluoroplasts possessing
hydrophilic, conductivity, improved solubility and better processibility. Thus, for
example, the introduction of bromotrifluoroethylene to the composition of
polytetrafluoroethylene increases amphoterism of the copolymer and reduces its melting
temperature (5).
Bromine-containing monomers, for example 1-bromo-2,2-difluoroethylene, have found wide
application in processes of copolymerization with TFE, VDF, hexafluoropropylene and other
fluoroolefins to produce fluoroelastomers and general rubber goods based on rubbers (6-9).
In this case bromine atoms are convenient active centers to form space-network structures
(10-16). There are known many polymer compositions of radical solidification based on
bromated and iodinated fluoroelastomers (17-21).
It was planned to produce new fluoroplasts and fluoroelastomers with a set of performance
characteristics peculiar to copolymers based both on perfluoroalkylvinyl ethers and on
bromine-containing fluoromonomers using BrAVE monomers as modifiers of fluoropolymers in
reactions of copolymerization with fluoroolefins.
In the present paper we state the results of the determination of general physical and
mechanical characteristics of copolymers of BrAVE with the most widespread fluoromonomers,
TFE and VDF, and their resistance in different aggressive chemical media.
2.Test procedure
Physical and mechanical characteristics of materials were determined on the basis of
the results of tensile tests carried out on a test machine of 2055 P-05 type of
"TochPribor" (c. Ivanovo, Russia) made.
Test samples were two-sided scoops manufactured by blanking from films with a special
knife. The machine is equipped with a hermetic autoclave of a special design with
controllable electrical heating to provide testing the samples in different aggressive
chemical media.
Based on the tensile test results the following physical and mechanical characteristics
were calculated:
- breaking stress, MPa
 , MPa
where Pp is the load at the sample destruction, N
Fo is the starting surface of the sample cross-section, cm;
- modulus of elasticity, MPa
 , MPa
where P1,P2 are the loads chosen at the
initial linear part of the tensile diagram, N;
 l1,l2 - are the
sample elongation at the loads of P1,P2 respectively, cm;
lo- is the length of the sample test part, cm;
- percent elongation
where lp
is the sample elongation at rupture, cm;
- percentage change of the breaking stress
where  p1 is the breaking
stress in a medium, MPa;
p2 is the breaking
stress in air, MPa;
- percentage of the modulus of elasticity
where Ep1 is the modulus of elasticity in a medium, MPa;
Epo is the modulus of elasticity in air, MPa
- change of percent elongation
where  p1 is the percent
elongation in a medium, %;
po is the percent elongation in
air,%.
To determine chemical resistance of the copolymers, samples were subjected to aging for 7
days in 20% solutions of sulfuric acid and caustic soda at a temperature of 90oC
and then their physical and mechanical properties were determined at tensile at 20oC.
2. Study of physical and mechanical characteristics of copolymers
of TFE.
The fluoroplast of F-10 type widely used for making flexible pipelines, gasket
materials etc. was used as the comparison standard.
The comparison of modificating affect of BrAVE monomer and other fluoromonomers such as -fluorosulfuryl-perfluoroalkylvinyl
ether (FS-141), perfluoroallylvinyl ether , perfluoroallylalkylvinyl diether was of an
undoubted interest also. Some results of the conducted experiments are given in Table1.
The study has shown that the strength characteristics and modulus of elasticity
considerably increase after treatment in alkali for almost all types of copolymers of TFE
tested. Some reduction in the modulus of elasticity of copolymers with FS-141 was observed
in tests in sulfuric acid against a background of some increase in the strength
parameters. Deformation characteristics of the all copolymers of FS-141 tested ( with
different content of comonomer) are reduced in aggressive media and to a greater degree in
aging in alkali.
As regards to BrAVE monomers, all their physical and mechanical parameters increase both
in acid and in alkali media and the modulus of elasticity and breaking stress increase to
the greatest extent.
It is seen from Table 1 that effectiveness of BrAVE monomers goes down with the chain
length growth. The increase in the strength characteristics of copolymers based on BrAVE
after their aging both in acid and in alkali is explained by additional cross-linking of
the copolymer which takes place at the contact of the bromine-containing copolymer with an
aggressive medium.
The modificating ability of perfluoroallylvinyl ether is considerably lower than
that of bromine-containing and sulfofluoride fluoromonomers.
The data given in Table 1 allow to conclude that aggressive chemical media affect
significantly the physical and mechanical parameters of all copolymers investigated and
this influence is ambiguous. The properties of the copolymer of TFE with FS-141 in alkali
are the most negatively affected including the increase in brittleness .
Table 1. Physical and mechanical properties of copolymers of TFE.
Sample
state |
Copolymer name and its
content,%(mole) |
Temperature,oC |
Physical
and mechanical characteristics of copolymers |
| p , ÌÏà |
Ep, ÌÏà |
Ep,% |
,% |
Ep,% |
p,% |
| Initial without processing |
F-10
13-BrAVE-2
17-BrAVE-4
7-perfluoroallylvinyl ether
14-FS-141 |
20
20
20
20
20 |
23,9 17,7
17,7
6,7
24,9 |
- 242
-
-
281 |
220 175
230
165
215 |
-
-
-
-
- |
-
-
-
-
- |
-
-
-
-
- |
| After aging in acid |
F-10
13-BrAVE-2
17-BrAVE-4
7-perfluoroallylvinyl ether
14-FS-141
13-BrAVE-2
14-FS-141 |
20
20
20
20
20
90
90 |
21,8 25,5
19,0
5,8
30
5,3
12,6 |
- 406
-
-
202
55,7
41,5 |
235 177
285
100
212
93
155 |
-9 44
7
-13
19
-
- |
- 68
-
-
-28 |
7 1
24
-39
-1 |
| After aging in alkali |
F-10
13-BrAVE-2
17-BrAVE-4
7-perfluoroallylvinyl ether
14-FS-141
13-BrAVE-2
14-FS-141 |
20
20
20
20
20
90
90 |
22,1 25,5
20,7
6,5
34,9
4,9
18,1 |
- 431
-
-
298
35,3
61,1 |
235 191
290
185
98
55
223 |
-7 44
17
-3
38
-
- |
- 78
-
-
6
-
- |
3 9
26
12
-54
-
- |
Experiments at elevated temperature confirm the mentioned above tendency to increase the
brittleness of copolymers under exposure to aggressive media, and the reduction in
deformability becomes most apparent for copolymers with BrAVE (up to 68%).
The most probable cause of the found phenomenon is complex affect of aging in acid and
alkali over a long period of time as well as direct influence of these media on the
materials during the process of deformation of films and predominance of the corresponding
influence depends on conditions of testing and maintenance.
3.Study of physical and mechanical characteristics of copolymers
of VDF.
The physical and mechanical parameters of the copolymers based on VDF as the results of
the study are given in Table 2.
They witness that most of the copolymers investigated are relatively chemically unstable
in one of media as minimum, including VDF homopolymer, with the exception of comonomers of
VDF with BrAVE which are most resistant both in acid and in alkali media. Some samples
showed an increase in the general characteristics, for example breaking tensile stress and
percent elongation at rupture attained almost 200%. In contrast to copolymers of TFE with
BrAVE, the influence of the chain length in the fluoroalkyl fragment of BrAVE monomers for
fluoropolymers based on VDF is not so great and the influence on strength and deformation
characteristics is of opposite character, in particular in acid media.
Table 2. Physical and mechanical properties of copolymers of VDF
Sample
state |
Copolymer name and its
content,%(mole) |
Physical
and mechanical characteristics of copolymers |
p ,
ÌÏà |
Ep,
ÌÏà |
p ,% |
Ep,% |
| Initial without processing |
PVDF
0,3-BrAVE2
9-BrAVE-4
0,5-perfluoroallylvinyl ether
1,3 perfluoroallylalkylvinyl diether |
58,5
45
24,7
46
27,5 |
23
19,5
25
56
6 |
- -
-
-
- |
- -
-
-
- |
| After aging in acid |
PVDF
0,3-BrAVE-2
9-BrAVE-4
0,5-perfluoroallylvinyl ether
1,3 perfluoroallylalkylvinyl diether |
48
54
3,2
46,5
25,7 |
16
17
45
45
7 |
-18
20
-32
1
-7 |
-30
-13
80
-20
17 |
| After aging in alkali |
PVDF
0,3-BrAVE-2
9-BrAVE-4
0,5-perfluoroallylvinyl ether
1,3perfluoroallylalkylvinyl diether |
58
53,5
6,6
54
14,9 |
36
23,5
17
15,5
3 |
-1
19
40
17
-46 |
57
21
-3
-12
-50 |
4. Conclusions
The main physical and mechanical parameters of copolymers of tetrafluoroethylene and
vinylidene fluoride with -bromo-perfluoroalkylvinyl
ethers and related sulfofluoride monomers and fluoromonomers of polyene structure have
been determined.
It has been found experimentally that bromine-containing fluoromonomers of BrAVE are
highly active modifiers of fluoropolymers. Fluorinated copolymers on their base are stable
both in acid and in alkali media and they possess better physical and mechanical
properties compared with base fluoropolymers and this is peculiar both to
tetrafluoroethylene and to vinylidene fluoride.
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