CA1283129C - Pyrolysis of perfluoropolyethers - Google Patents
Pyrolysis of perfluoropolyethersInfo
- Publication number
- CA1283129C CA1283129C CA000522463A CA522463A CA1283129C CA 1283129 C CA1283129 C CA 1283129C CA 000522463 A CA000522463 A CA 000522463A CA 522463 A CA522463 A CA 522463A CA 1283129 C CA1283129 C CA 1283129C
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- Canada
- Prior art keywords
- molecular weight
- lower molecular
- perfluoropolyethers
- perfluoropolyether
- perfluoropoly
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
- C08G65/002—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from unsaturated compounds
- C08G65/005—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from unsaturated compounds containing halogens
- C08G65/007—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from unsaturated compounds containing halogens containing fluorine
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G65/00—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule
- C08G65/02—Macromolecular compounds obtained by reactions forming an ether link in the main chain of the macromolecule from cyclic ethers by opening of the heterocyclic ring
- C08G65/32—Polymers modified by chemical after-treatment
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- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Lubricants (AREA)
- Polyethers (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of breaking down perfluoropolyethers into lower molecular weight fragments by pyrolysis is disclosed. The perfluoropolyethers are pyrolyzed generally at 500-600°C. Volatile lower molecular weight components are condensed and colleted.
Various molecular weight fractions can be obtained by taking appropriate distillation cuts.
A method of breaking down perfluoropolyethers into lower molecular weight fragments by pyrolysis is disclosed. The perfluoropolyethers are pyrolyzed generally at 500-600°C. Volatile lower molecular weight components are condensed and colleted.
Various molecular weight fractions can be obtained by taking appropriate distillation cuts.
Description
~33~
THE PYROLYSIS OF PERFLUOROPOLYETHERS
Field of the Invention This invention is in the fields of polymer and fluorine chemistry.
05 Background Preparation of saturated perfluoropolyethers has traditionally been limited because of the lack of versatile synthetic techniques. A successful synthesis is the polymerization of perfluoro-epoxides, particularly hexafluoropropylene oxide andtetrafluoroethylene oxide. W. T. Miller, U. S~
Patent 3,242,218. This synthetic procedure involves a three-step scheme for production of the polymer involving oxidation of perfluoroolefins to per~luoro-epoxides, followed by anionic polymerization to acylfluoride terminated perfluoropolyethers and then replacement of the acyl fluoride end groups with perfluoroalkyl groups by decarboxylation reactions or by chain coupling photolytic decarboxylation reactions.
T~e procedure, however, allows little control over the molecular weight distribution o~ the product. Typically, a distillation cut is taken if a specific molecular weight range is needed. When tetrafluoroethylene oxide is polymerized, little if any low molecular weight fluids are obtained; the majority of the product is a higher molecular weight solid. Conversely, the polymerization of perfluoro-propylene oxide gives only a liquid; no products : ' - , ' ' ' ' :
:
3~
are isolated with a su~ficiently high molecular weight to be solid.
An alternate synthetic method for the pro-duction of perfluoropolyethers involves the ultra-05 violet photolysis of tetrafluoroethylene and/orhexa~luoropropylene in an iner-t solvent in the presence of oxygen, D. Sianesi and R. Fontanelli, British Patent 1,226,566. The multistep process yields an acyl fluoride terminated polymer which contains unstable peroxidic linkages in addition to difluoromethylene oxide and tetrafluorethylene oxide (or hexafluoropropylene oxide) repeating units.
Treatment of the polymer at elevated temperatures and with fluorine gas gives a stable polymer con-taining only perfluoroalkyl end groups. Once again, it is very difficult to control the molecular weight of the polymer product. The product can be sepa-rated into various fractions based on vapor pres-sure.
There exists a need ~or a convenient means to alter the molecular weight of a perfluoropolyether polymer.
Disclosure of the Invention This invention pertains to a method of cleaving ~5 per~luoropolyethers to give lower molecular weight polymers. ~he method comprises pyroiysis of a perfluoropolyether, condensation and collection of vaporized lower molecular weight ~ragments o~ the perfluoropolyether.
In one embodiment o~ the method, the pyrolysis is carried out in an apparatus which separates the high molecular weight polymer from the desir~d lower molecular weight fraction on the basis o~ vapor pressure ~e.g. a distillation apparatus). The perfluoropolyether to be pyrolyzed is placed into a 05 crucible or other vessel (pyrolysis vessel) which is located in a heating zone of the apparatus. Pre-ferably, the apparatus has means -for introduction o~
and exit of a gas and an inert gas is passed over the polymer throughout the procedure. The polymer is heated to pyrolysis temperature, about 350-600C, preferably 500-600C, by raising the temperature in the heating zone and the polymer is maintained at that temperature to allow low molecular weight ~ragments to vaporize and distill out of the pyroly-sis vessel. The low molecular weight products are collected upon condensation generally in a collec-tion vessel attached to the condensing zone of the distillation apparatus.
The pyrolysis can be carried out using a pure perfluoropolyether, generally in solid form.
Additives such as select metal oxides can be added to the perfluoropolyether in order to catalytically reduce the temperature required for pyrolysis.
; Carbon-carbon cross-links present in the polymer to be pyrolyzed may be eliminated by adding MaOH or KOII prior to pyrolysis. These age~ts break the cross-links pre~erentially at the temperatures used ; (about 50G-60~C)~
The pyrolysis may be done in the presence of f].uorine gas so that when the polymers are cleaved, ; the radicals resulting from bond breakage are capped with ~luorine. Alternatively, the recovered lower .
?
., . :
, ~3~
molecular weight fractions may be treated with elemental fluorine after pyrolysis to ensure satura-tion and terminal group capping with fluorine.
~rief Description of the Drawings 05 The Figure illustrates a simple apparatus for conducting the pyrolysis procedure of the invention.
Best Mode of the Invention The pyrolysis procedure of this invention can be carried out in a variety of apparati. A simple design is shown schematically in the Figure. It consists of a nickel tube with one removable flange (A) sealed to the reactor using an O-ring (TeflonT
O-ring3. Suspended in the chamber near the top is a nickel crucible (B) which is used to hold the per-fluoropolyether which is to be pyrolyzed. A furnace (C) is placed around the nickel tube in the viclnityof the lower one-half of the crucible. A gas diluent enters through the top inlet (D) and exits along with the pyrolyzed fluid through (E). A collection vessel is attached to the bottom of the vessel to collect and hold the fluid. If fluorine is used as the pyrolysis gas, a fluorine scrubber is at-tached downstream from the collection vessel.
The perfluoropolyether is placed in the nickel crucible. The temperature at the bottom of the crucible is raised to about 35~-600C, preferably 500-600C and held at that temperature (the tempera-ture at the top of the crucible can be variable depending on the location of the heater). The polymer 3~
is refluxed until a sufficient number of bonds are broken to allow the lower molecular weight fragments to distill out of the pyroylsis vessel. A stream of inert gas (e.g. nitrogen) sweeps the fragment vapors 05 from the reactor into the collection vessel. Fluorine gas or a fluorine gas/inert gas mixture can be used in place of the inert gas as described in detail below.
Many other reactor designs can be used success-fully. ~irtually any type of distillation apparatus which can be heated to 500C preferably in the pre-sence of fluorine gas and hydrogen fluoride, can be used. In general, a suitable apparatus comprises:
i) a sample vessel (pyrolysis vessel) located in a heating zone;
ii) a condensing zone;
iii) a collection vessel connected by passage-way to the condensing zone; and iv) means for introduction of a gas.
The pyrolysis procedure of this invention is applicable for all saturated perfluoropolyethers.
This techni~ue can be employed to crack perfluoro-polyethers of any molecular weight including high molecular weight solids and low molecular weight low viscosity fluids. Because perf~uoropolyethers are oxidatively stable at 500C and because bond breakage occurs preferentially over oxidation, inert gases, such as helium, can be used or ~trong oxidi~ers, such as oxygen, air, or fluorine, work satisfactorily.
~ pyrolysis temperature of 500C appears to be optimal to pyrolyze approximately 1/2 pound of 1~8~3~J
~6--perfluoropolyether each hour (e.g. in a 3" pyrolysis tube). If the pyrolysis is carried out in ~luorine, a delivery rate of approximately lcc/min is needed for each gram pyrolyzed. The procedure can be performed 05 at ambient pressure for most applications but it should be recognized that an increase in pressure can be used to lower the molecular weight distribution while a decrease in pressure has the opposite effect.
~his pressure dependence ~5 observed since the pyrolysis products distill from the high temperature zone.
The yield obtained is a ~unction of the mclecular weight distribution. Due to the random nature of bond breakage, a loss in yield occurs only when a fra~nent is formed which is too small to be of any use. If the average molecular weight is known and if the lowest useable molecular weight is identified, then an approximate yield can be estimated using simple statistical methods. For example if an average molecular weight of 5000 is desired, approximatPly 87 of the sample will have a molecular weight above 700.
As mentioned, virtu~lly any perfluoropolyether can be pyrolyzed to give lower molecular weight polymers by the method of this invention. For example, polyhexa~luoropropylene oxide, when heated to 500C, randomly breaks apart giving low ~iscosity ~luids. Other examples include per~luoro(polyethylene oxide) ~olyme;s, ~er~luoroethylene oxide/pr~pylene oxide copolymers, per~luoro(polytetramethylene oxide) and per~luoropolycyclohexyl oxide polymers.
Perfluoropolyethers are chemically well suited ~or this reaction since they do not depolymeriæe by .' ' ' ' :
~' ' ' .
3~2~3 eliminating monomer units in a sequential manner as many polymers do. Additionally, perfluoropolyethers can break down completely at elevated tempera-tures in both an inert a-tmosphere and in an oxidizing atmos-05 phere without leaving a nonvolatile residue.
Although -the discussions to this point have dealt wlth the pyrolysis of perfluoropolyethers in a neat form, the reac-tions can be carried out with other materials present. For exarnple, perfluoropolyethers prepared via direct fluorination may contain NaHF2 or NaF because NaF can be added as a HF scavenger.
See Canadian Patent Application Serial No. 522,462, filed November 7, 1986, entitled "Perfluorination of Ethers". Mixtures containing NaF/NaHF2 concentra-tions as high as 90% can be successfully pyrolyzed.
In addition, additives such as metal fluoride (e.g.
titanium fluoride and aluminum fluoride) or metal oxide (e.g. aluminum oxide) can be added to cataly-tically reduce the temperature required for pyrolysis.Further, sodium hydroxide or potassium hydroxide can be blended into the polymer prior to pyrolysis to improve the linearity of the fluid produced by breaking any incidental cross-links which may be present in the higher molecular weight polymer.
The pyrolysis procedure can be perforrned in the presence of 1uorine gas. If cleavage occurs in the presence of elemental fluorine~ the radicals resulting from bond breakage are capped with fluorine. The thermal cracking of perfluoropolyethylene oxide in the C
1~3~;~9 presence of fluorine gas primarily leads to carbon-carbon and carbon-oxygen bond cleavage. The carbon-carbon bond, beiny the weaker of the two, is broken preferentially as illustrated by the following 05 equations:
CF30(CF2-CF2 O)nCF3 3 2 2 )m CF2 ~ CF2-0(CF2-CF2-o) ( -CF
3 2 2 0)mCF3+CF3-o(CF2-CF2-0) CF
If carbon-oxygen bond is broken, an unstable acyl fluoride is formed which decomposes to give a perfluoro-alkyl terminal group as depicted by the following reaction sequence:
CF-O(CF2-CF2-O)nCF3 ?
o(cF?-CF -0~ CF2-cF2-~-o(cF2 CF2 )n-(m+l) 3 3 2 2 )mC2Fs ~ CF30(CF2-CF2_o) ( )CF
~ COF2 It is often desirable to carry out the pyroly-sis in an inert atmosphere to avoid having to handle hot fluorine gas. T~is can be done success-fully ana usually results in acyl fluoride termi-i ~0 nated polymers which contain a slight degree o~
unsaturation resulting in very slight discolora-tions. The acyl fluoride end groups and unsatu-ration can be easily eliminated by treatment ;
;. ' , ~83~
g of the polymer with fluorine gas at 110C aftar pyrolysis.
The invention is illustrated further by the following example.
05 Example 1 The nickel crucible shown in the Figure was filled with 700g of perfluoropolyethylene oxide solids. The crucible (nickel tube, outside diameter 2~ inches, length 12 inches) was placed in the nickel pyrolysis tube (outside diameter, 3 inches;
length 2 feet) and was purged with several volumes of nitrogen prior to heating. The crucible was heated to the pyrolysis temperature (500C) over a two hour period and was maintained at that tempera-ture for approximately three hours to ensure thatall of the polymer is thermally cracked. The lower molecular weight fragments distilled out of the crucible which was held at a temperature of approxi-mately 350C at the top. A purge of nitrogen (50cc/min) through the pyrolysis tube swept the oil vapors rom the reactor into a collection vessel.
609g of a light oil was collected (87~ yield) which was slightly discolored and contained some acyl fluoride terminal groups. Treatment of the oil with pure ~luorine at 110C in an ambient pressure reactor gave 581g of a clear, nonreactive, light oil ~overall ~iéld of 83~).
le 2 The apparatu5 of Example 1 was charged with 650g of a medium viscosity perfluoropolyethylene ~331~9 oxide fluid (viscosity at 100F was approximat~ly 100 centistokes). The crucible was placed in the nickel pyrolysis tube which was purged with several volumes of nitrogen and pressured with 2S0 psi of o5 nitrogen. A nitrogen purge through the pressurized vessel was maintained as the crucible was heated to the pyrolysis temperature (500-600C). This temperature was maintained for approximately 3 hours which allowed the lower molecular weight fragments to distill out of the crucible and into a collection vessel as they were produced. Approximately 580y of a light oil was recovered having a viscosity of 15-20 centistokes at 100F.
Example 3 -The apparatus of Example I was filled with 725g of a perfluorinated 70:30 ethylene oxide:propylene oxide copolvmer~ The crucible was placed in the nickel pyrolysis tube, was loaded in the pyrolysis apparatus, and was purged with several volumes of nitrogen prior to heating to 500C. The lower molecular weight fragments distilled out of the xeactor as they were produced giving rise to 630g of a pale yellow oil which contained some acyl fluoride terminal groups. Titration of the oil with a 1 molar NaOH solution (phenothalein end point) showed that approximately 25~ of the terminal groups were reacti~!e acyl 1uoride groups. Treatment of the o'l at 110C in pure fluorine gave 610g of a clear, chemically inert, light oil which was shown to be a perfluoro(ethylene oxide-propylene oxide) copolymer by F nmr.
~118 Example ~
Approximately SOOg of perfluoropropylene oxide solids (prepared by direct fluorination of propylene oxide) were placed in a nickel crucible which was 05 positioned in the nickel pyrolysis vessel depicted in Figure I. Following purging with several volumes of nitrogen, the apparatus was heated to 500C over a 2 hour period and was maintained at that tempera-ture for approximately 3 hours as the solids were thermally cracked. The lower molecular weight ~ragments distilled out of the crucible which was held at a temperature of approximately 350C at the top~ Approximately 430g of a yellow oil was reco-vered in the collection ~essel. Treatment of the fluid with pure fluorine for several hours (110C) gave a medium viscosity fluid with a 19F nmr indis-tinguishable from that of a Rrytox fluid with a comparable viscosity. (Krytox is the trademark of a perfluoropolyether fluid based on hexa~luoropropylene oxide which is marketed by Du Pont).
Industrial Applicability Perfluoropolyether fluids, due to their ext~eme stability and chemical inertness, are useful for many applications such as hydraulic fluids, sol-vents, lubricants, sealants, etc. However, their uses are currently numbered due to synthetic limi-tations which prevent the preparation of a fluid with the proper molecular weight distribution. The pyrolysis method of this invention can be used to produce low molecular perfluoropolyether fluids from 831~9 high molecular weight solids (or fluids). By incorporating this pyrolysis technology with existing polymerization or direct fluorination technologies for producing perfluoropolyethers, 05 essentially all molecular weight ranges of perfluoro polyethers can be made in fairly high vields.
Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experi-mentation, many equivalents to the speci~ic embodi-ments o~ the invention described herein. Such equivalents are intended to be encompassed by the following claims.
THE PYROLYSIS OF PERFLUOROPOLYETHERS
Field of the Invention This invention is in the fields of polymer and fluorine chemistry.
05 Background Preparation of saturated perfluoropolyethers has traditionally been limited because of the lack of versatile synthetic techniques. A successful synthesis is the polymerization of perfluoro-epoxides, particularly hexafluoropropylene oxide andtetrafluoroethylene oxide. W. T. Miller, U. S~
Patent 3,242,218. This synthetic procedure involves a three-step scheme for production of the polymer involving oxidation of perfluoroolefins to per~luoro-epoxides, followed by anionic polymerization to acylfluoride terminated perfluoropolyethers and then replacement of the acyl fluoride end groups with perfluoroalkyl groups by decarboxylation reactions or by chain coupling photolytic decarboxylation reactions.
T~e procedure, however, allows little control over the molecular weight distribution o~ the product. Typically, a distillation cut is taken if a specific molecular weight range is needed. When tetrafluoroethylene oxide is polymerized, little if any low molecular weight fluids are obtained; the majority of the product is a higher molecular weight solid. Conversely, the polymerization of perfluoro-propylene oxide gives only a liquid; no products : ' - , ' ' ' ' :
:
3~
are isolated with a su~ficiently high molecular weight to be solid.
An alternate synthetic method for the pro-duction of perfluoropolyethers involves the ultra-05 violet photolysis of tetrafluoroethylene and/orhexa~luoropropylene in an iner-t solvent in the presence of oxygen, D. Sianesi and R. Fontanelli, British Patent 1,226,566. The multistep process yields an acyl fluoride terminated polymer which contains unstable peroxidic linkages in addition to difluoromethylene oxide and tetrafluorethylene oxide (or hexafluoropropylene oxide) repeating units.
Treatment of the polymer at elevated temperatures and with fluorine gas gives a stable polymer con-taining only perfluoroalkyl end groups. Once again, it is very difficult to control the molecular weight of the polymer product. The product can be sepa-rated into various fractions based on vapor pres-sure.
There exists a need ~or a convenient means to alter the molecular weight of a perfluoropolyether polymer.
Disclosure of the Invention This invention pertains to a method of cleaving ~5 per~luoropolyethers to give lower molecular weight polymers. ~he method comprises pyroiysis of a perfluoropolyether, condensation and collection of vaporized lower molecular weight ~ragments o~ the perfluoropolyether.
In one embodiment o~ the method, the pyrolysis is carried out in an apparatus which separates the high molecular weight polymer from the desir~d lower molecular weight fraction on the basis o~ vapor pressure ~e.g. a distillation apparatus). The perfluoropolyether to be pyrolyzed is placed into a 05 crucible or other vessel (pyrolysis vessel) which is located in a heating zone of the apparatus. Pre-ferably, the apparatus has means -for introduction o~
and exit of a gas and an inert gas is passed over the polymer throughout the procedure. The polymer is heated to pyrolysis temperature, about 350-600C, preferably 500-600C, by raising the temperature in the heating zone and the polymer is maintained at that temperature to allow low molecular weight ~ragments to vaporize and distill out of the pyroly-sis vessel. The low molecular weight products are collected upon condensation generally in a collec-tion vessel attached to the condensing zone of the distillation apparatus.
The pyrolysis can be carried out using a pure perfluoropolyether, generally in solid form.
Additives such as select metal oxides can be added to the perfluoropolyether in order to catalytically reduce the temperature required for pyrolysis.
; Carbon-carbon cross-links present in the polymer to be pyrolyzed may be eliminated by adding MaOH or KOII prior to pyrolysis. These age~ts break the cross-links pre~erentially at the temperatures used ; (about 50G-60~C)~
The pyrolysis may be done in the presence of f].uorine gas so that when the polymers are cleaved, ; the radicals resulting from bond breakage are capped with ~luorine. Alternatively, the recovered lower .
?
., . :
, ~3~
molecular weight fractions may be treated with elemental fluorine after pyrolysis to ensure satura-tion and terminal group capping with fluorine.
~rief Description of the Drawings 05 The Figure illustrates a simple apparatus for conducting the pyrolysis procedure of the invention.
Best Mode of the Invention The pyrolysis procedure of this invention can be carried out in a variety of apparati. A simple design is shown schematically in the Figure. It consists of a nickel tube with one removable flange (A) sealed to the reactor using an O-ring (TeflonT
O-ring3. Suspended in the chamber near the top is a nickel crucible (B) which is used to hold the per-fluoropolyether which is to be pyrolyzed. A furnace (C) is placed around the nickel tube in the viclnityof the lower one-half of the crucible. A gas diluent enters through the top inlet (D) and exits along with the pyrolyzed fluid through (E). A collection vessel is attached to the bottom of the vessel to collect and hold the fluid. If fluorine is used as the pyrolysis gas, a fluorine scrubber is at-tached downstream from the collection vessel.
The perfluoropolyether is placed in the nickel crucible. The temperature at the bottom of the crucible is raised to about 35~-600C, preferably 500-600C and held at that temperature (the tempera-ture at the top of the crucible can be variable depending on the location of the heater). The polymer 3~
is refluxed until a sufficient number of bonds are broken to allow the lower molecular weight fragments to distill out of the pyroylsis vessel. A stream of inert gas (e.g. nitrogen) sweeps the fragment vapors 05 from the reactor into the collection vessel. Fluorine gas or a fluorine gas/inert gas mixture can be used in place of the inert gas as described in detail below.
Many other reactor designs can be used success-fully. ~irtually any type of distillation apparatus which can be heated to 500C preferably in the pre-sence of fluorine gas and hydrogen fluoride, can be used. In general, a suitable apparatus comprises:
i) a sample vessel (pyrolysis vessel) located in a heating zone;
ii) a condensing zone;
iii) a collection vessel connected by passage-way to the condensing zone; and iv) means for introduction of a gas.
The pyrolysis procedure of this invention is applicable for all saturated perfluoropolyethers.
This techni~ue can be employed to crack perfluoro-polyethers of any molecular weight including high molecular weight solids and low molecular weight low viscosity fluids. Because perf~uoropolyethers are oxidatively stable at 500C and because bond breakage occurs preferentially over oxidation, inert gases, such as helium, can be used or ~trong oxidi~ers, such as oxygen, air, or fluorine, work satisfactorily.
~ pyrolysis temperature of 500C appears to be optimal to pyrolyze approximately 1/2 pound of 1~8~3~J
~6--perfluoropolyether each hour (e.g. in a 3" pyrolysis tube). If the pyrolysis is carried out in ~luorine, a delivery rate of approximately lcc/min is needed for each gram pyrolyzed. The procedure can be performed 05 at ambient pressure for most applications but it should be recognized that an increase in pressure can be used to lower the molecular weight distribution while a decrease in pressure has the opposite effect.
~his pressure dependence ~5 observed since the pyrolysis products distill from the high temperature zone.
The yield obtained is a ~unction of the mclecular weight distribution. Due to the random nature of bond breakage, a loss in yield occurs only when a fra~nent is formed which is too small to be of any use. If the average molecular weight is known and if the lowest useable molecular weight is identified, then an approximate yield can be estimated using simple statistical methods. For example if an average molecular weight of 5000 is desired, approximatPly 87 of the sample will have a molecular weight above 700.
As mentioned, virtu~lly any perfluoropolyether can be pyrolyzed to give lower molecular weight polymers by the method of this invention. For example, polyhexa~luoropropylene oxide, when heated to 500C, randomly breaks apart giving low ~iscosity ~luids. Other examples include per~luoro(polyethylene oxide) ~olyme;s, ~er~luoroethylene oxide/pr~pylene oxide copolymers, per~luoro(polytetramethylene oxide) and per~luoropolycyclohexyl oxide polymers.
Perfluoropolyethers are chemically well suited ~or this reaction since they do not depolymeriæe by .' ' ' ' :
~' ' ' .
3~2~3 eliminating monomer units in a sequential manner as many polymers do. Additionally, perfluoropolyethers can break down completely at elevated tempera-tures in both an inert a-tmosphere and in an oxidizing atmos-05 phere without leaving a nonvolatile residue.
Although -the discussions to this point have dealt wlth the pyrolysis of perfluoropolyethers in a neat form, the reac-tions can be carried out with other materials present. For exarnple, perfluoropolyethers prepared via direct fluorination may contain NaHF2 or NaF because NaF can be added as a HF scavenger.
See Canadian Patent Application Serial No. 522,462, filed November 7, 1986, entitled "Perfluorination of Ethers". Mixtures containing NaF/NaHF2 concentra-tions as high as 90% can be successfully pyrolyzed.
In addition, additives such as metal fluoride (e.g.
titanium fluoride and aluminum fluoride) or metal oxide (e.g. aluminum oxide) can be added to cataly-tically reduce the temperature required for pyrolysis.Further, sodium hydroxide or potassium hydroxide can be blended into the polymer prior to pyrolysis to improve the linearity of the fluid produced by breaking any incidental cross-links which may be present in the higher molecular weight polymer.
The pyrolysis procedure can be perforrned in the presence of 1uorine gas. If cleavage occurs in the presence of elemental fluorine~ the radicals resulting from bond breakage are capped with fluorine. The thermal cracking of perfluoropolyethylene oxide in the C
1~3~;~9 presence of fluorine gas primarily leads to carbon-carbon and carbon-oxygen bond cleavage. The carbon-carbon bond, beiny the weaker of the two, is broken preferentially as illustrated by the following 05 equations:
CF30(CF2-CF2 O)nCF3 3 2 2 )m CF2 ~ CF2-0(CF2-CF2-o) ( -CF
3 2 2 0)mCF3+CF3-o(CF2-CF2-0) CF
If carbon-oxygen bond is broken, an unstable acyl fluoride is formed which decomposes to give a perfluoro-alkyl terminal group as depicted by the following reaction sequence:
CF-O(CF2-CF2-O)nCF3 ?
o(cF?-CF -0~ CF2-cF2-~-o(cF2 CF2 )n-(m+l) 3 3 2 2 )mC2Fs ~ CF30(CF2-CF2_o) ( )CF
~ COF2 It is often desirable to carry out the pyroly-sis in an inert atmosphere to avoid having to handle hot fluorine gas. T~is can be done success-fully ana usually results in acyl fluoride termi-i ~0 nated polymers which contain a slight degree o~
unsaturation resulting in very slight discolora-tions. The acyl fluoride end groups and unsatu-ration can be easily eliminated by treatment ;
;. ' , ~83~
g of the polymer with fluorine gas at 110C aftar pyrolysis.
The invention is illustrated further by the following example.
05 Example 1 The nickel crucible shown in the Figure was filled with 700g of perfluoropolyethylene oxide solids. The crucible (nickel tube, outside diameter 2~ inches, length 12 inches) was placed in the nickel pyrolysis tube (outside diameter, 3 inches;
length 2 feet) and was purged with several volumes of nitrogen prior to heating. The crucible was heated to the pyrolysis temperature (500C) over a two hour period and was maintained at that tempera-ture for approximately three hours to ensure thatall of the polymer is thermally cracked. The lower molecular weight fragments distilled out of the crucible which was held at a temperature of approxi-mately 350C at the top. A purge of nitrogen (50cc/min) through the pyrolysis tube swept the oil vapors rom the reactor into a collection vessel.
609g of a light oil was collected (87~ yield) which was slightly discolored and contained some acyl fluoride terminal groups. Treatment of the oil with pure ~luorine at 110C in an ambient pressure reactor gave 581g of a clear, nonreactive, light oil ~overall ~iéld of 83~).
le 2 The apparatu5 of Example 1 was charged with 650g of a medium viscosity perfluoropolyethylene ~331~9 oxide fluid (viscosity at 100F was approximat~ly 100 centistokes). The crucible was placed in the nickel pyrolysis tube which was purged with several volumes of nitrogen and pressured with 2S0 psi of o5 nitrogen. A nitrogen purge through the pressurized vessel was maintained as the crucible was heated to the pyrolysis temperature (500-600C). This temperature was maintained for approximately 3 hours which allowed the lower molecular weight fragments to distill out of the crucible and into a collection vessel as they were produced. Approximately 580y of a light oil was recovered having a viscosity of 15-20 centistokes at 100F.
Example 3 -The apparatus of Example I was filled with 725g of a perfluorinated 70:30 ethylene oxide:propylene oxide copolvmer~ The crucible was placed in the nickel pyrolysis tube, was loaded in the pyrolysis apparatus, and was purged with several volumes of nitrogen prior to heating to 500C. The lower molecular weight fragments distilled out of the xeactor as they were produced giving rise to 630g of a pale yellow oil which contained some acyl fluoride terminal groups. Titration of the oil with a 1 molar NaOH solution (phenothalein end point) showed that approximately 25~ of the terminal groups were reacti~!e acyl 1uoride groups. Treatment of the o'l at 110C in pure fluorine gave 610g of a clear, chemically inert, light oil which was shown to be a perfluoro(ethylene oxide-propylene oxide) copolymer by F nmr.
~118 Example ~
Approximately SOOg of perfluoropropylene oxide solids (prepared by direct fluorination of propylene oxide) were placed in a nickel crucible which was 05 positioned in the nickel pyrolysis vessel depicted in Figure I. Following purging with several volumes of nitrogen, the apparatus was heated to 500C over a 2 hour period and was maintained at that tempera-ture for approximately 3 hours as the solids were thermally cracked. The lower molecular weight ~ragments distilled out of the crucible which was held at a temperature of approximately 350C at the top~ Approximately 430g of a yellow oil was reco-vered in the collection ~essel. Treatment of the fluid with pure fluorine for several hours (110C) gave a medium viscosity fluid with a 19F nmr indis-tinguishable from that of a Rrytox fluid with a comparable viscosity. (Krytox is the trademark of a perfluoropolyether fluid based on hexa~luoropropylene oxide which is marketed by Du Pont).
Industrial Applicability Perfluoropolyether fluids, due to their ext~eme stability and chemical inertness, are useful for many applications such as hydraulic fluids, sol-vents, lubricants, sealants, etc. However, their uses are currently numbered due to synthetic limi-tations which prevent the preparation of a fluid with the proper molecular weight distribution. The pyrolysis method of this invention can be used to produce low molecular perfluoropolyether fluids from 831~9 high molecular weight solids (or fluids). By incorporating this pyrolysis technology with existing polymerization or direct fluorination technologies for producing perfluoropolyethers, 05 essentially all molecular weight ranges of perfluoro polyethers can be made in fairly high vields.
Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine experi-mentation, many equivalents to the speci~ic embodi-ments o~ the invention described herein. Such equivalents are intended to be encompassed by the following claims.
Claims (18)
1. A method of cleaving perfluoropolyethers to lower molecular weight fragments, comprising the steps of:
a) pyrolyzing a perfluoropolyether at a tem-perature above about 350°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropolyethers, in the absence of a metal oxide or metal fluoride catalyst;
b) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers; and c) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
a) pyrolyzing a perfluoropolyether at a tem-perature above about 350°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropolyethers, in the absence of a metal oxide or metal fluoride catalyst;
b) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers; and c) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
2. A method of claim 1, wherein the perfluoro-polyether is pyrolyzed in the presence of an inert gas.
3. A method of claim 1, wherein the perfluoro-polyether is pyrolyzed in the presence of fluorine gas or a mixture of inert gas and fluorine gas.
4. A method of breaking down perfluoropolyethers into lower molecular weight polymers, comprising the steps of:
a) providing a distillation apparatus com-prising:
i) a sample vessel located in a heating zone;
ii) a condensing zone;
iii) a collection vessel connected by pas-sageway to the condensing zone; and iv) means for introduction of a gas;
b) placing a perfluoropolyether in a sample vessel;
c) establishing a flow of inert gas into the apparatus;
d) heating the perfluoropolyether by raising the temperature of the heating zone to above 350°C to cleave the perfluoropoly-ether into lower molecular weight linear perfluoropolyethers, in the absence of a metal oxide or metal fluoride catalyst;
e) maintaining the temperature in the heating zone to vaporize the lower molecular weight linear perfluoropolyethers;
f) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers; and g) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
a) providing a distillation apparatus com-prising:
i) a sample vessel located in a heating zone;
ii) a condensing zone;
iii) a collection vessel connected by pas-sageway to the condensing zone; and iv) means for introduction of a gas;
b) placing a perfluoropolyether in a sample vessel;
c) establishing a flow of inert gas into the apparatus;
d) heating the perfluoropolyether by raising the temperature of the heating zone to above 350°C to cleave the perfluoropoly-ether into lower molecular weight linear perfluoropolyethers, in the absence of a metal oxide or metal fluoride catalyst;
e) maintaining the temperature in the heating zone to vaporize the lower molecular weight linear perfluoropolyethers;
f) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers; and g) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
5. A method of cleaving perfluoropolyether solids to produce perfluoropolyether oils, comprising the steps of:
a) heating a solid perfluoropolyether to a temperature above 350°C to cleave the per-fluoropolyether into lower molecular weight linear fragments, in the absence of a metal oxide or metal fluoride catalyst;
b) condensing and collecting vaporized lower molecular weight linear fragments to obtain an oil; and c) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
a) heating a solid perfluoropolyether to a temperature above 350°C to cleave the per-fluoropolyether into lower molecular weight linear fragments, in the absence of a metal oxide or metal fluoride catalyst;
b) condensing and collecting vaporized lower molecular weight linear fragments to obtain an oil; and c) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
6. A method of cleaving perfluoropolyethers to lower molecular weight fragments, comprising the steps of:
a) pyrolyzing a perfluoropolyether at a tem-perature above from about 500°C-600°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropoly-ethers;
b) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers; and c) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
a) pyrolyzing a perfluoropolyether at a tem-perature above from about 500°C-600°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropoly-ethers;
b) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers; and c) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
7. A method of claim 6, wherein the metal oxide is added to the perfluoropolyether before pyrolysis.
8. A method of claim 6, wherein the step of pyrolyzing is performed in a distillation apparatus, comprising:
a) a sample vessel located in a heating zone;
b) a condensing zone;
c) a collection vessel connected by passageway to the condensing zone; and d) means for introduction of a gas.
a) a sample vessel located in a heating zone;
b) a condensing zone;
c) a collection vessel connected by passageway to the condensing zone; and d) means for introduction of a gas.
9. A method of claim 6, wherein a perfluoropoly-ether oil is produced by pyrolyzing a solid perfluoro-polyether.
10. A method of cleaving perfluoropolyethers to lower molecular weight fragments, comprising the steps of:
a) providing a perfluoropolyether selected from the group consisting of perfluoropoly (ethylene oxide), perfluoropolypropylene oxide, perfluoroethylene oxide/propylene oxide copolymers, perfluoropoly-(tetra-methylene oxide) and perfluoropoly-(cyclo-hexyl oxide);
b) pyrolyzing the perfluoropolyether at a temperature above about 350°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropolyethers, in the absence of a metal oxide or metal fluoride catalyst; and c) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers.
a) providing a perfluoropolyether selected from the group consisting of perfluoropoly (ethylene oxide), perfluoropolypropylene oxide, perfluoroethylene oxide/propylene oxide copolymers, perfluoropoly-(tetra-methylene oxide) and perfluoropoly-(cyclo-hexyl oxide);
b) pyrolyzing the perfluoropolyether at a temperature above about 350°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropolyethers, in the absence of a metal oxide or metal fluoride catalyst; and c) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers.
11. A method of claim 10, further comprising the step of:
d) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
d) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
12. A method of claim 10, wherein the step of pyrolyzing is performed in a distillation apparatus, comprising:
a) a sample vessel located in a heating zone b) a condensing zone;
c) a collection vessel connected by passageway to the condensing zone; and d) means for introduction of a gas.
a) a sample vessel located in a heating zone b) a condensing zone;
c) a collection vessel connected by passageway to the condensing zone; and d) means for introduction of a gas.
13. A method of claim 10, wherein a perfluoropoly-ether oil is produced by pyrolyzing a solid perfluoro-polyether.
14. A method of cleaving perfluoropolyethers to lower molecular weight fragments, comprising the steps of:
a) providing a perfluoropolyether selected from the group consisting of perfluoropoly (ethylene oxide), perfluoropolypropylene oxide, perfluoroethylene oxide/propylene oxide copolymers, perfluoropoly(tetrame-thylene oxide) and perfluoropoly-(cyclo-hexyl oxide);
b) pyrolyzing the perfluoropolyether at a temperature above from about 500°C-600°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropoly-ethers; and c) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers.
a) providing a perfluoropolyether selected from the group consisting of perfluoropoly (ethylene oxide), perfluoropolypropylene oxide, perfluoroethylene oxide/propylene oxide copolymers, perfluoropoly(tetrame-thylene oxide) and perfluoropoly-(cyclo-hexyl oxide);
b) pyrolyzing the perfluoropolyether at a temperature above from about 500°C-600°C to cleave the perfluoropolyether into lower molecular weight linear perfluoropoly-ethers; and c) condensing and collecting vaporized lower molecular weight linear perfluoropoly-ethers.
15. A method of claim 14, further comprising the step of:
d) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
d) treating the collected linear perfluoro-polyethers with fluorine gas to eliminate acyl fluoride end groups and any unsatura-tion of the collected perfluoropolyethers.
16. A method of claim 14, wherein the step of pyrolyzing is performed in a distillation apparatus, comprising:
a) a sample vessel located in a heating zone;
b) a condensing zone;
c) a collection vessel connected by passageway to the condensing zone; and d) means for introduction of a gas.
a) a sample vessel located in a heating zone;
b) a condensing zone;
c) a collection vessel connected by passageway to the condensing zone; and d) means for introduction of a gas.
17. A method of claim 14, wherein a perfluoropoly-ether oil is produced by pyrolyzing a solid perfluoro-polyether.
18
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79662485A | 1985-11-08 | 1985-11-08 | |
| US796,624 | 1985-11-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1283129C true CA1283129C (en) | 1991-04-16 |
Family
ID=25168638
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000522463A Expired - Fee Related CA1283129C (en) | 1985-11-08 | 1986-11-07 | Pyrolysis of perfluoropolyethers |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0256024A1 (en) |
| JP (1) | JPS63501299A (en) |
| KR (1) | KR880700838A (en) |
| BR (1) | BR8606970A (en) |
| CA (1) | CA1283129C (en) |
| WO (1) | WO1987002995A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0848623B1 (en) | 1996-07-05 | 2003-10-08 | Disetronic Licensing AG | Injection device for injection of liquid |
| CN115181257B (en) * | 2022-08-09 | 2023-06-09 | 浙江巨化技术中心有限公司 | Method for reducing molecular weight of perfluoropolyether |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3242218A (en) * | 1961-03-29 | 1966-03-22 | Du Pont | Process for preparing fluorocarbon polyethers |
| FR1530862A (en) * | 1966-07-11 | 1968-06-28 | Montedison Spa | Fluorinated ketones and process for preparing them |
| IL31863A0 (en) * | 1968-04-23 | 1969-05-28 | Du Pont | 4-phenyl(substituted bicyclo(2.2.2)octene)-1-carboxylic acids related compounds and pharmaceutical compositions containing them |
| US3847978A (en) * | 1968-07-01 | 1974-11-12 | Montedison Spa | Perfluorinated linear polyethers having reactive terminal groups at both ends of the chain and process for the preparation thereof |
| BE764110A (en) * | 1970-03-12 | 1971-09-13 | Montedison Spa | Cyclic perfluoro polyethers |
| US4523039A (en) * | 1980-04-11 | 1985-06-11 | The University Of Texas | Method for forming perfluorocarbon ethers |
| AU579374B2 (en) * | 1984-05-23 | 1988-11-24 | Ausimont S.R.L. | Process for preparing perfluoropolyethers with neutral and functional end-groups, having a regulated molecular weight |
-
1986
- 1986-10-31 BR BR8606970A patent/BR8606970A/en unknown
- 1986-10-31 WO PCT/US1986/002345 patent/WO1987002995A1/en not_active Application Discontinuation
- 1986-10-31 EP EP86907094A patent/EP0256024A1/en not_active Withdrawn
- 1986-10-31 JP JP61506093A patent/JPS63501299A/en active Pending
- 1986-11-07 CA CA000522463A patent/CA1283129C/en not_active Expired - Fee Related
-
1987
- 1987-07-08 KR KR870700593A patent/KR880700838A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| AU6622186A (en) | 1987-06-02 |
| EP0256024A1 (en) | 1988-02-24 |
| WO1987002995A1 (en) | 1987-05-21 |
| AU590646B2 (en) | 1989-11-09 |
| KR880700838A (en) | 1988-04-12 |
| BR8606970A (en) | 1987-12-01 |
| JPS63501299A (en) | 1988-05-19 |
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