Thermoplastic fluorinated polymers

Details Thermoplastic fluorinated polymers Thermoplastic fluorinated polymers

2002-05-22

2003-05-20

Zitomer, Fred (Department: 1713)

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

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S544000, C524S545000, C524S556000, C524S560000, C524S562000, C524S570000

Reexamination Certificate

active

06566442

ABSTRACT:

The present invention relates to thermoprocessable flexible fluorinated polymers.
More specifically the present invention relates to flexible copolymers of ethylene/tetrafluoroethylene (ETFE) and ethylene/chlorotrifluoroethylene (ECTFE), modified with hydrogenated monomers. Said copolymers are used for obtaining sheets, pipes, and manufactured articles, among which flexible cables, i.e. having a low elastic modulus, are preferred. More specifically, for the application of flexible cables, said copolymers must not show a necking at yield on the stress-strain curve, thus avoiding the whitening effect on the bent cable. The whitening effect visually represents the material plastic deformation wherefore this cannot recover any longer the initial state.
Ethylene/tetrafluoroethylene (ETFE) and ethylene/chlorotrifluoroethylene (ECTFE) (co)polymers modified with hydrogenated monomers to which flexibility (low elastic modulus) is conferred by addition of hydrogenated plasticizers, are known in the prior art.
One disadvantage of these plasticized (co)polymers when used in the chemical process industry (CPI) is that the plasticizers can migrate from the polymer polluting the process fluids and reducing the manufactured article flexibility.
In the case of the wire & cable applications, for safety reasons these flexible cables must show a high time to ignition, a low smoke and heat releases when they are subjected to a heat source such as for example in the cone calorimeter (see ASTM E1354 test). However the presence of plasticizers increases the release of smoke and heat when the manufactured article comes into direct contact with the flame. Besides, the presence of plasticizers increases the polymer dielectric constant, which is undesired for cables.
The need was therefore felt to have available flexible ethylene/tetrafluoroethylene (ETFE) and ethylene/chlorotrifluoroethylene (ECTFE) (co)polymers not plasticized.
An object of the present invention is therefore a composition comprising a polymer mixture A of polymers formed by moles:
(a) from 10 to 70%, preferably from 35 to 55%, of ethylene (E),
(b) from 30 to 90%, preferably from 45 to 65%, of a fluorinated monomer selected from tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), or mixtures thereof,
(c) from 0.1 to 30%, preferably from 1 to 15%, with respect to the total amount of monomers (a) and (b), of one or more acrylic monomers of formula:
CH
2
═CH—CO—O—R
2
  (I)
wherein R
2
is a linear and/or branched alkyl radical, C
1
-C
20
, from 1 to 20 carbon atoms, or cycloalkyl from 3 to 20 carbon atoms, or R
2
is H; the R
2
radical can optionally contain: heteroatoms preferably Cl, O, N; one or more functional groups preferably selected from OH, COOH, epoxide, ester and ether; and double bonds;
characterized in that the polymer mixture A comprises polymer fractions having a different content of the comonomer of formula (I) such that the elastic modulus at 23° C. (ASTM D1708) of said polymer mixture A is lower than at least 10% of the elastic modulus of a polymer formed by monomers a), b) and c) wherein the polymer fractions have substantially an equal content of the comonomer of formula (I).
The polymer mixture A of the composition of the invention is obtainable by blend. For example at least two polymers A1 and A2 can be mixed comprising the monomers of the invention wherein the comonomer of formula (I) in the copolymer A2 is at least 1.5 times the amount of comonomer of formula (I) in the copolymer A1. The ratio by weight between the copolymers A1/A2 is preferably comprised between 1/9 and 9/1.
Preferably the amount of comonomer of formula (I) in the copolymer A2 is at least 1.75 times the amount of comonomer of formula (I) in the copolymer A1, the ratio by weight between the copolymers A1/A2 being preferably comprised between 1/4 and 4/1.
Still more preferably the composition is characterized in that the amount of comonomer of formula (I) in the copolymer A2 is at least twice the amount of comonomer of formula (I) in the copolymer A1, the ratio by weight between the copolymers A1/A2 being preferably between 3/7 and 7/3.
The blends can directly be obtained in polymerization or by physical mixing. Indeed, the polymer mixture A can be obtained by the synthesis in sequence of the polymer fractions in a single polymerization of the above mentioned monomers a), b) and c).
The acrylic monomers of formula (I) are selected from ethylacrylate, n-butylacrylate, acrylic acid, hydroxyethylacrylate, hydroxypropylacrylate, (hydroxy)ethylhexylacrylate.
Preferably the monomer of formula (I) is n-butyl acrylate.
Preferably the fluorinated monomer b) is chlorotrifluoroethylene (CTFE).
Another object of the present invention is the preparation of the polymer mixture A in polymerization, in which in a conversion range of ethylene equal to 50%, at least 75% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
Preferably the process is characterized in that in a conversion range of ethylene equal to 30%, at least 50% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
Furthermore preferably after 90% of ethylene conversion, less than 7% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
Furthermore still more preferably after 80% of ethylene conversion, less than 7% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
This preparation process of the polymer mixture A is a copolymerization of the corresponding monomers in the presence of radical initiators, in suspension in organic medium, in the presence or absence of water, or in aqueous emulsion, at a temperature in the range between −60° and 150° C., preferably between −20° and 100° C., more preferably between −10° and 50° C., and pressures in the range 0.5-100 bar, preferably 5-40 bar.
Among the radical initiators, that can be in particular used are:
(i) bis-acylperoxides of formula (R
f
—CO—O)
2
, wherein R
f
is a (per)haloalkyl C
1
-C
10
(see for example EP 185,242 and U.S. Pat. No. 4,513,129), or a perfluoropolyoxyalkylene group (see for example EP 186,215 and U.S. Pat. No. 5,021,516); among them, bis-trichloroacetylperoxide and bis-dichlorofluoroacetylperoxide are particularly preferred (see U.S. Pat. No. 5,569,728);
(ii) dialkylperoxides of formula (R
H
—O)
2
, wherein R
H
is an alkyl C
1
-C
10
; diterbutylperoxide (DTBP) is particularly preferred;
(iii) hydrosoluble inorganic peroxides, such as ammonium or alkaline metal persulphates or perphosphates; sodium and potassium persulphates are particularly preferred.
(iv) dialkylperoxydicarbonates, wherein the alkyl has from 1 to 8 carbon atoms, such as for example di-n-propyl-peroxydicarbonate and di-isopropyl-peroxydicarbonate (see EP 526,216);
(v) organic or inorganic redox systems, such as ammonium persulphate/sodium sulphite, hydrogen peroxide/aminoiminomethansulphinic acid, terbutylhydroperoxide/metabisulphite (see U.S. Pat. No. 5,453,477).
The molecular weight control of the polymer mixture A can be made by using the telogen activity of the comonomers of formula (I) comparable to that of a conventional chain transfer agent especially at high temperatures, i.e. in the range 20°-100° C., or by using specific chain transfer agents. Among these it can be mentioned: ketones, esters, ethers or aliphatic alcohols having from 3 to 10 carbon atoms; hydrocarbons or halogenated hydrocarbons, having from 1 to 6 carbon atoms; bis(alkyl)carbonates wherein the alkyl has from 1 to 5 carbon atoms; etc. Among them, chloroform and alkyl substituted cyclopentanes, in particular methylcyclopentane, are particularly preferred (see U.S. Pat. No. 5,510,435). The transfer agent is fed to the reactor at the beginning of the reaction, or in a continuous way or batchwise during the polymerization. The amount of the used chain transfer agent can range within rather wide limits, depending on the type of the used monomers, the reaction temperature and the molec

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