VDF thermoplastic copolymer

Details VDF thermoplastic copolymer VDF thermoplastic copolymer

1997-06-30

2001-03-13

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...

C526S206000, C526S209000, C526S210000

Reexamination Certificate

active

06201084

ABSTRACT:

The present invention relates to polyvinylidenfluoride having improved impact resistance.
In particular it refers to vinylidenfluoride thermoplatic copolymers.
It is well known that polyvinylidenfluoride (PVDF) is a crystalline polymer endowed with good properties of chemical and mechanical resistance, however it shows a marked brittleness and a clear tendency to the brittle fracture.
Therefore its employment where a good impact resistance and/or absence of brittle fracture, is required, for instance for the manufacture of structural elements (self-supporting pipes, flanges and the like) has various inconveniences and practically its use is limited to low thicknesses.
It is also known to improve the impact resistance of the PVDF homopolymer by copolymerization of vinylidenfluoride (VDF) with another fluoro-containing olefin as initial part of the monomer feeding in the autoclave or continuously fed with a fixed ratio with respect to VDF consumption. See for instance European patent EP 526216, examples 6 and 9; and the patents U.S. Pat. No. 4,569,978 example 15, repeated also in U.S. Pat. No. 5,093,427 (example 1 comparative). In particular the comonomer used is the hexafluoropropene (HFP) in amounts generally comprised between about 0.3 and 100% by moles.
The drawbacks of such processes reside in the fact that there is a decrease of the rating temperature of the material due to the lowering of the second melting temperature of the product.
To obviate this inconvenience, U.S. Pat. No. 5,093,427 suggests the addition of hexafluoropropene in autoclave after having consumed an amount of about 50-90% by weight of the total VDF used in polymerization. In this way one succeeds in substantially maintaining the second melting temperature of the homopolymer and therefore to keep the maximum rating temperature.
It is to be noticed, however, that the use of HFP as comonomer brings to a decay of the mechanical properties, such as for instance the elastic modulus and the yield-stress especially at high temperatures (150° C.).
The Applicant has now unexpectedly and surprisingly found that by using particular comonomers as specified hereunder it is possible to obtain VDF thermoplastic polymers having an improved impact resistance while maintaining the rating temperature of the homopolymer combined with good mechanical properties even at high temperatures.
An object of the present invention consists therefore in vinylidenfluoride (VDF) thermplastic copolymers, comprising:
(a) from 0.1 to 10% by moles, preferably from 0.5 to 5%, of one or more fluorodioxoles of formula:
 wherein Y is equal to OR
f
wherein R
f
is a perfluoroalkyl having from 1 to 5 carbon atoms, or Y═Z as defined hereinunder; Y is preferably equal to OR
f
; X
1
and X
2
, equal to or different from each other, are —F or —CF
3
; Z is selected from —F, —H, —Cl;
(b) VDF being the remaining part to 100% by moles.
Preferably in the formula (I) X
1
, X
2
and Z are —F; R
f
is preferably —CF
3
, —C
2
F
5
, or —C
3
F
7
. The fluorodioxoles of formula (I) wherein Y is equal to OR
f
in which R
f
is —CF
3
and X
1
, X
2
and Z are —F, are particularly preferred. This product is indicated hereinafter as TTD (2,2,4-trifluoro-5-trifluoro-metoxy-1,3-dioxole).
The fluorodioxole of formula (I) are described in U.S. Pat. No. 5,498,682 in the name of the Applicant, the content of which is incorporated herein by reference.
The copolymers of the present invention can be synthesized by copolymerizing VDF with fluorodioxoles also by introducing the comonomer at the beginning of the polymerization.
Another process that can be mentioned consists in adding the comonomer according to the system described in U.S. Pat. No. 5,093,427, herein incorporated by reference, i.e. the addition of the fluorodioxole in autoclave is carried out after having consumed an amount of about 50-90% by weight of the total VDF used in the polymerization.
The copolymers object of the present invention can be prepared according to known techniques, by copolymerizing the corresponding monomers, in suspension with or without water or in aqueous emulsion in the presence of a suitable radical initiator, at a temperature generally comprised from −40° C. to 130° C., preferably from −15° C. to 100° C., more preferably from −10° C. to 70° C. The reaction pressure is generally comprised between 0.5 anmd 150 bar, preferably betweem 2 and 90 bar.
Any product capable of generating active radicals at the chosen (co)polymerization temperature, can be employed as initiator. It can be chosen for instance from: inorganic peroxides, such as for instance sodium, potassium or ammonium peroxydisulphate; dialkylperoxides, such as for instance diterbutylperoxide (DTBP); dialkylperoxydicarbonates, such as for instance diethyl- and diisopropyl-peroxydicarbonate (IPP), bis-(4-t-butyl-cyclohexyl)-peroxydicarbonate; t-alkylperoxybenzoates; t-alkylperoxy-pivalates, such as for instance t-butyl and t-amyl perpivalate; acetylcyclohexansulphonyl peroxide; dibenzoyl peroxide; dicumylperoxide.
The amount of the radical initiator in reaction is the usual one for the copolymerization of fluoro-containing olefinic monomers, and is generally comprised between 0.003% and 4% by weight with respect to the total amount of (co)polymerized monomers.
The reaction is usually carried out in the presence of a suitable surfactant, see for instance those described in U.S. Pat. No. 4,360,652 and U.S. Pat. No. 4,025,709, so as to give a stable emulsion. They are generally fluoro-containing surfactants, chosen from the products of the general formula
R
f′
—X
−
M
+
wherein R
f′
is a (per)fluoroalkyl chain C
5
-C
14
or a (per)fluoropolyoxyalkylenic chain, X
−
is —COO
−
or —SO
3
−
, M
+
is chosen from H
+
, NH
4
+
, an alkaline metal ion. Among the most commonly used we remember: ammonium perfluoro-octanoate; (per)fluoropolyoxyalkylenes terminated with one or more carboxylic groups; salts of sulphonic acids having the formula R
f″
—C
2
H
4
SO
3
H, wherein R
f″
is a perfluoroalkyl C
4
-C
10
(see the patent U.S. Pat. No. 4025709); etc.
To adjust the molecular weight of the final polymer, a chain transfer agent can be added to the reaction medium. This can be chosen for instance from: ketones, esters, ethers or aliphatic alcohols having from 3 to 10 carbon atoms, such as acetone, ethylacetate, diethylether, isopropyl alcohol, etc.: chloro(fluoro)carbons, optionally containing hydrogen, having from 1 to 6 carbon atoms, such as chloroform, trichlorofluoromethane, 1,1,1-trifluoro-2,2-dichloroethane (HCFC-123), etc.; bis(alkyl)carbonates in which the alkyl has from 1 to 5 carbon atoms, such as bis(ethyl)-carbonate, bis(isobutyl)carbonate; etc.
The amount of chain transfer agent used can range within very wide limits, depending on the molecular weight meant to be obtained, on the effectiveness of the transfer agent and on the reaction temperature. Such amount is generally comprised between 0.05 and 5%, preferably between 0.1 and 2.4% by weight with respect to the total amount of monomers fed in the reactor.
In the suspension polymerization in the presence of water, stabilizers, for instance polyvinylalcohols, methylcellulose, etc. (U.S. Pat. No. 4,946,900) can be added to the reaction mixture. Mineral oils or paraffins, liquid at the synthesis temperature, can also be used in the emulsion polymerization of the VDF (see U.S. Pat. No. 4,076,929).
The process object of the present invention can be advantageously carried out in the presence of: emulsions or microemulsions of pefluoropolyoxyalkylenes, according to U.S. Pat. No. 4,789,717 and U.S. Pat. No. 4,864,006; microemulsions of fluoropolyoxyalkylenes having hydrogen-containing end groups and/or hydrogen-containing repeating units, according to European patent application EP 625,526, herein incorporated by reference, and microemulsions of fluoropolyoxyalkylens having hydrogen-containing end groups and/or hydrogen-containing repeating units and hydrocarbons C
1
-C
20
, preferably C
1
-

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