,- •DO NOT DESTROY

WADC TECHNICAL REPORT 52-197 RETURN TODOCUMENTS CONTROL

PART VIII BRANCH '--ASTIA DOCUMENT No. AD 142114/.. FILE COPY

"ALOG"ED BY WCOSI

SYNTHETIC RUBBERS

FROM CARBON-FLUORINE COMPOUNDS

CARL L. SANDBERG

MINNESOTA MINING AND MANUFACTURING COMPANY

NOVEMBER 1957

This report is not to be announced or distributedautomatically in accordance with AFR 205-43A,

paragraph 6d.

WRIGHT AIR DEVELOPMENT CENTER

Statement AApproved for Public Release

NOTICES

When Government drawings, specifications, or other data are used for any purpose otherthan in connection with a definitely related Government procurement operation, the United StatesGovernment thereby incurs no responsibility nor any obligation whatsoever; and the fact thatthe Government may have formulated, furnished, or in any way supplied the said drawings,specifications, or other data, is not to be regarded by implication or otherwise as in any mannerlicensing the holder or any other person or corporation, or conveying any rights or permissionto manufacture, use, or sell any patented invention that may in any way be related thereto.

Qualified requesters may obtain copies of this report from the ASTIA Document ServiceCenter, Knott Building, Dayton 2, Ohio.

Copies of WADC Technical Reports and Technical Notes should not be returned to the WrightAir Development Center unless return is required by security considerations, contractual obliga-tions, or notice on a specific document.

WADC TECHNICAL REPORT 52-197

PART VIII

ASTIA DOCUMENT No. AD 142114

SYNTHETIC RUBBERS

FROM CARBON-FLUORINE COMPOUNDS

CARL L. SANDBERG

MINNESOTA MINING AND MANUFACTURING COMPANY

NOVEMBER 1957

MATERIALS LABORATORY

CONTRACT No. AF 33(038)-515

PROJECT No. 7340

WRIGHT AIR DEVELOPMENT CENTER

AIR RESEARCH AND DEVELOPMENT COMMAND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

Carpenter Litho & Prtg. Co., Springfield, 0.400 - December 1957

FOREWORD

This report was prepared by the Minnesote Mining and ManufacturingCoVpany under USAF Contract No. AF 33(038)-515. This contract weeinitiated under Project No. 7340, "Rubber, Plastic, and Composite Mater-ai88', Task No. 73405, lCoupounding of Elastomers . It was administered

under the direction of the Materipls Laborptory, Directorpte of laboratories,Wright Air Development Center with Lt. I. M. Kelble eating as projectengineer,

This report covers the neriod from December 15, 1956 to -une 15, 1957.

The nonomers which constitute the raw materials used in the workunder the contract, viz., polymerization studies and evaluation of polywers,are available only through the use of contractor's personnel and facilities,and constitute approximately 35% of the effort involved in the contrFetduring this period. This leaves approximatoly 65% of said effort as repre-senting the actual polymerization studies end evaluation of polymers reportedherein.

WAUC e 52-197 Pt VIII

ABSTRACT

Further evalUation of 3(4J -chloroperfluoroethoxy)-l,l-dihydroperfluoropropyl acrylate has shown it to be comparable toother perfluoro alkoxy acrylates in low temperature propertiesand resistance to aromatic solvents and hot air aging, but some-what poorer in resistance to oxygenated solvents and to diesterlubricants.

Attempts to homopolymerize 1,2-epoxyperfluoroheptane withperoxide catalysts or with a ferric chloride:propylene oxidecatalyst have given mainly reaction products and little evidenceof polymerization. Attempts to copolymerize 1,2-epoxyperfluoro-heptane with propylene oxide, using a ferric chloride:propyleneoxide catalyst, have given viscous liquid products which maybe copolymers.

Exploratory copolymerizations of perfluoro-2-azapropene withvinyl-type monomers have given products containing small amountsof the azapropene.

PUBLICATION REVIEW

This report has been reviewed and is approved.

FOR THE COMMANDER:

R. T. SCHWARTZChief, Organic Materials BranchMaterials Laboratory

WADC TR 52-197 Pt VIII iii

TABLE OF CONTENTS

Page

INTRODUCTION ....................... ................ ... . 1

FLUORINE-CONTAINING ACRYLATES ....... ...................... . 2

FLUORINATED OLEFIN OXIDES ................ ............... . .. 6

1. Polymerization of Hydrocarbon Olefin Oxides ..... 6

2. Reaction of 1,2-Epoxyperfluoroheptane (EFH) withFree-Radical Catalysts .......................... 10

3. Reaction of 1,2-Epoxyperfluoroheptane (EFH) with

FeC1 3 :Propylene Oxide Catalyst .................. 10

4. Copolymerization of EFH with Propylene Oxide .... 11

FLUOROCARBON NITROGEN MONOMERS ........................... 13

SUMMARY AND CONCLUSIONS .. .... .......... .. .. ............ . 15 II

APPENDIX ....... o .......... t .......V I o .......... 16

WADC TR 52-197 Pt VIII iv

LIST OF ABBREVIATIONS

Cl-FEFPA 3( W -Chaloroperfluoroetl-ioxy)-1,1-dihiydroperfluoro-propyl acrylate, C1CF2CF2OCF2CF2CH2OCOCH=-CH 2

H-FEFPA 3 (W( -H-ydroperfluoroetbhoxy) -1, 1-dihydroiperfluoro-propyl acrylate, HCF2 CF200F2CF2CH2000CH=CH2

2F4 ~ 3M Brand Fluoro-Rubber 2F4~, PolY-3-perfluoro-metbhoxy-1,1-dibhydroperfluoropro'pyl acrylate,CF 3 OC F2 CF2 CH2 0000H=--CH 2

EFH 1, 2-Epox-yperfluorolieptane, C5Fll-CF-CF20

PrO Propylene Oxide, CH3-O\.rH0

FAP Perfluoro-2-azapropene, CF3 -N=CF2

WADO TR 52-197 Pt VIIIv

INTRODUCTION

The research effort supported by this contract has led to newsolvent-resistant and heat-resistant fluorine-containing poly-acrylate rubbers. Some additional exploratory work is reportedhere, but the major effort has now shifted to other fluorine-containing polymers. Fluorine-containing polysiloxanes werestudied during the last contract period.

A study of the polymerization of the fluorinated olefin ox-ide RfCF,-F 2 was initiated during the present contract. Monomers

of this type are available through the contractor's facilities,and during the past six months polymerization studies on 1,2-epoxyperfluoroheptane have constituted the major portion of thework carried out under the contract. A few additional experi-ments with 3(W) -chloroperfluoroethoxy) -1,1-dihydroperfluoropropylacrylate and some copolymerization experiments with a new mon-omer, perfluoro-2-azapropene, CF3 -N=CF 2 have also been carriedout.

Manuscript released by author November 1, 1957 for publicationas a WADC Technical Report.

WADC TR 52-197 Pt VIII 1

FLUORINE-CONTAINING ACRYLATES

Two additional homopolymers of 3(i)-chloroperfluoroethoxy)-l,l-dihydroperfluoropropyl acrylate (()-Cl-FEFPA) and two copoly-mers with added acrylic acid were prepared in the standard emulsionrecipe. (See Appendix 1 for recipe). Analyses of this lot ofCi-FEFPA monomer indicates that it contains the requisite amountof chlorine and that only 0.02% acrylic acid has been carried overfrom the esterification step. Polymerization data are given inTable I. The products were obtained by freezing the latexes,washing the polymer with water and then drying in vacuo at 50*C.The polymers are soft rubbers of high molecular weight.

Polymers were compounded and cured using the standard aminerecipe (see Appendix 2). Properties of the vulcanizates aregiven in Table II, along with comparative data for scme otherfluorine-containing alkoxy acrylate rubbers synthesized underthis contract.

The Cl-FEFPA vulcanizates are rather low in tensile strength,and no improvement was observed with the two copolymers contain-ing additional acrylic acid. Resistance to solvents at roomtemperature is good and the hot turbo oil resistance is fair,considering the low initial tensile value.

The Cl-FEFPA vulcanizates show the good low temperatureproperties characteristic of the other fluorine-containing alkoxyacrylates, such as 3M Brand Fluoro-Rubber 2F4. Resistance toaromatic fuels is very good, but somewhat higher swelling isobserved in oxygenated solvents. This behavior is also observedfor the W-hydro analog, H-FEFPA. Dry heat resistance is compar-able to that of 2F4, but resistance to diester lubricants issomewhat inferior.

This additional evaluation of Cl-FEFPA rubber and the processfor preparing it has not shown sufficient promise, relative tothe other alkoxy acrylates, to require further study at this time.Attention has, therefore, turned to two other monomer systemsdescribed in the following sections.

WADC TR 52-197 Pt VIII 2

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WADO TR 5Z-197 Pt VIII 5

FLUORINATED OLEFIN OXIDES

The polymerization of partially fl orinated olefin oxides hasbeen studied at other laboratories /1,2/ and products varying fromsolids to liquids have been reported. The use of acid catalystssuch as BF 3 , AIC1 3 , and FeC1 3 led to fairly high molecular weightpolymers. Polymers of perfluoroolefin oxides have not yet beendescribed.

A new fluorinated olefin oxide, 1,2-epoxyperfluoroheptane,C5FIlR!•F2, has been examined in homopolymerization and copolym-

0erization experiments. These experiments are described in detailbelow and in Tables III, IV, and V. The olefin oxide was care-fully fractionated through a 60-plate Todd column and a centercut (b.p. 81.5 0 C. uncorrected) reserved for use. Infrared spec-tra and gas chromatography indicate that this cut is very nearlya single, pure compound.

1. Polymerization of Hydrocarbon Olefin Oxides

In preparation for work with the fluorinated olefin oxide,the polymerization of propylene oxide and butylene oxide(straight chain isomers) was studied. Catalysts such as KOH, BF 3etherate, and FeCl 3 were examined and yielded low molecularweight products. The FeC13:.pr2 ,ylene oxide adduct catalyst des-cribed by Pruitt and Baggett 7-) and used by Price and coworkers/4,5/gave somewhat better results. Good yields of moderate molecular

/1/ Pierce, O.R., Smith, D. D., and Murch, R. M. "Fluorine-Con-taining Polyethers", WADC Technical Report 55-193, UnitedStates Air Force, Air Research and Development Command.

/2/ Jones, F. B., Lichtenwalter, C. A., Stickney, P. B., andHeilegmann, R. G., "Polymerization Studies on Monomersand Evaluation of Derivative Polymers", WADC TechnicalReport 57-110, United States Air Force, Air Research andDevelopment Command.

/3/ Pruitt, M. E. and Baggett, J. M., "Catalysts for the Polym-erization of Olefin Oxides", U.S. Patent 2,706,181.

/4/ Price, C. C., Osgan, M., Hughes, R. E. and Shambelan, C.,"The Polymerization of L-Propylene Oxide", J.A.C.S. 78,690 (1956).

/1/ Price, C. C. and Osgan, M., ibid, p. 4787.

WADC TR 52-197 Pt VIII 6

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WADO TR 52-197 Pt VIII 7

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weight polymer were obtained with propylene oxide and a FeCIl:propylene oxide catalyst prepared according to the patent. Thebest products were obtained when carefully fractionated monomerwas used and when precautions were taken to exclude moisturefrom the catalyst.

2. Reaction of 1,2-Epoxyperfluoroheptane (EFH) with Free-RadicalCatalysts

Prolonged heating of EFH with several types of free radicalinitiators gave small yields of dark, solid products. These werenot completely identified but appear to be largely mixtures ofreaction products, with possibly a small amount of low polymer.Details of the reaction are given in Table III.

The product from reaction 7-3 was examined in more detail.The product softens at about 70'C. and is soluble in acetone.Infrared analysis indicates a high concentration of fluorocarbonC=O and OH. Elemental analysis indicates loss of fluorine.(Found: 22.6% C, 50.6% F; Theory: 23.0% C, 72.7% F). Silicontetrafluoride was the major component of the gas recovered fromthe glass reaction tube, also indicating that fluoride had splitout from the epoxide. One of the reactions occurring appearsto be ring opening followed by rearrangement to an acid fluoride.Apparently this reaction may also be accompanied by more deep-seated rearrangements involving fragmentation of the molecule.

Products obtained with alkyl peroxide and hydroperoxidecatalysts indicate that ring opening and rearrangement may alsooccur on heating with these catalysts, but the extent of reactionis somewhat less than when acyl peroxides are used.

Neutralization of the products with KOH indicates that insome cases 25% of the reacted epoxide groups were converted toacid or acid fluoride. Under more mild reaction conditions, con-versions were lower, but product distribution appeared similar.

3. Reaction of 1,2-Epoxyperfluoroheptane (EFH) with FeCl 3 :Propylene Oxide Catalyst.

In another series of homopolymerization experiments (Tab )e IV)in glass ampoules, the ferric chloride:propylene oxide adduct/3,4,5/was used as a catalyst. In most of these experiments the ferricchloride:propylene oxide catalyst was prepared in the polymeriza-tion ampoule. It was thus possible to avoid the inconvenientstep of weighing the syrupy catalyst into the polymerization tube.In experiment 13-4, 1.0 ml. of a 5.5% solution of FeCla in an-hydrous ether was pipetted into a dry, nitrogen-flushea ampoule.The tube was chilled in liquid nitrogen while continuing thenitrogen flushing. To the cold tube, 0.4 ml. of propylene oxide

WADC TR 52-197 Pt VIII 10

was added and the tube was then evacuated and sealed. The mixturewas shaken one hour at 000. and one hour at 259C., opened andimmediately pumped on a vacuum system to remove the volatile prod-ucts. The ampoule was then filled with nitrogen and chilled,5.0 g. EFH was added, and the tube was evacuated and sealed. Itwas then placed in a heated (80 to 1050C.) rocking tube assemblyfor reaction.

The products were separated into gas, volatile liquid, andviscous portions. Silicon tetrafluoride was the major constituentof the gas phase, again indicating loss of fluoride from theepoxide. About 50 to 90% of the charges were recovered as low-boiling liquids and consisted mainly of unreacted EFH. Non-volatile,brown, viscous syrups were obtained in 5 to 35% yields and wereshown by infrared analyses to contain substantial amounts offluorocarbon C=0 and some OH, These products appear to be largelymixtures of reaction products, with possibly a small amount oflow molecular weight polymer. Infrared analysis indicates thatthese products are similar to those prepared with peroxide cata-lysts. Elemental analysis and neutralization numbers also indicatethis similarity.

Anhydrous ferric chloride has not appeared to be as active acatalyst as the ferric chloride:propylene oxide adduct.

The attempts to polymerize EFH at elevated temperatures, ingeneral, gave mixed reaction products in yields up to about 50%.A small amount of low polymer appeared to have formed in someexperiments. Attempts to separate the products were onlypartially successful and the nature of the reactions occurringare, therefore, not yet known.

4. Copolymerization of EFH with Propylene Oxide

Attempts to copolymerize EFH with approximately equal partsof propylene oxide resulted in high conversions to viscous liquidproducts. The ferric chloride:propylene oxide catalyst was usedin these experiments and prepared as described earlier. Experi-mental details are given in Table V. Attempts to react chargesricher in EFH gave products more closely resembling those obtainedwith EFH alone.

Product 6554-13-5 was obtained in 100% yield from a charge of2.0 g. EFH and 2.5 g. propylene oxide. (Under comparable condi-tions, a 10% conversion would be obtained with EFH alone).Approximately 10% of the product was low molecular weight poly-propylene oxide. The remainder was a tan, viscous syrup whichsplit into two equal parts when extracted with cyclic C6F120.The ether-soluble material contained 43.5% F (corresponding to

WADC TR 52-197 Pt VIII 11

19 mole %, calculated as EFH), whereas the insoluble material con-tained 24.6% F (7.5 mole % EFH). Infrared analysis of the twoportions shows much less of the anomolous C=O absorption in theether-insoluble portion than in the soluble portion or the originalmixture. Absorptions associated with the C-0 groups of poly-propylene oxide were also diminished and C-F bands were stronger.The ratio of C=O to C-F absorption is considerably lower thanfor reaction products obtained with EFH alone, suggesting thatthe undesirable rearrangement to acid fluoride may have been sup-pressed. The product is quite low molecular weight (inherentviscosity in benzene -O.01) and soluble in most organic solvents.A suitable procedure for separation of the mixed product is neededto prove copolymerization, but has not been found so far. Thepossibility that the product is a mixture of polypropylene oxideand EFH reaction products is unlikely, but has not yet been dis-proved.

Experiments in which the charges were approximately equimolarEFH and propylene oxide gave products more like those obtainedwith EFH alone, but in better conversion. Additional experimentsare needed to cover the entire range of charge compositions.

WADC TR 52-197 Pt VIII 12

FLUOROCARBON NITROGEN MONOMERS

The preparatio, nof, some nitrogen analogs of perfluoroolefinshas been described/,' 7 / recently in the literature. The homo-polymer of one member of the series, CF3 -N=CF2, has been reported/ 8 !but the product had not been characterized. A small amount ofCF3-N=CF 2 (perfluoro-2-azapropene, FAP) has been prepared in thislaboratory and was used in exploratory copolymerization withvinyl type monomers.

The FAP monomer was prepared by the procedure of Young/7/,starting with dimethyl amine and involving the following seriesof reactions:

(CH3 ) 2 NH COCl2;• (CH3 ) 2 NCOC1 cell (CF 3 ) 2 NCOF pyrolyze CF3 -N=CF 2

A total of 25 g. of product (b.p. -34°C.) was obtained.

Comonomers used with FAP include the following: vinylacetate, vinyl isobutyl ether, styrene, ethyl acrylate, acrylo-nitrile, chlorotrifluoroethylene, and vinyl 1,1-dihydroperfluoro-butyl ether. Polymerizations were carried out in bulk at 50°c.,using benzoyl peroxide and t-butyl hydroperoxide initiators.Details are given in Table VI.

In most cases, the products contained small amounts of FAP,based on nitrogen analysis. Product 16-8, a crumbly solidobtained with FAP and vinyl 1,1-dihydroperfluorobutyl ether, wasobtained in 28% yield and contained 17 mole % FAP. With vinylacetate, vinyl isobutyl ether, and chlorotrifluoroethylene, smallamounts of FAP entered the polymer. Products resulting fromattempts to copolymerize FAP with styrene, ethyl acrylate, andacrylonitrile do not as yet appear to contain any perfluoro-2-azapropene.

/6/ Barr, D. A. and Haszeldine, R. N., "Perfluoroalkyl Deriva-tives of Nitrogen, Part 1", J.Chem.Soc., 1881 (1955).

/7/ Young, J. A., Simmons, T. C. and Hoffmann, F. W., "Fluoro-carbon Nitrogen Compounds. Perfluoro Carbonic AcidDerivatives", J.A.C.S. 78, 5637 (1956).

/8/ Brown, H. E., Dresdner, R. D., Wethington, J. A. Jr., andYoung, J. A., "Preparation of Fluorine-Containing Compounds",WADC Technical Report 56-234, United States Air Force, AirResearch and Development Command.

WADC TR 52-197 Pt VIII 13

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TR \2-19 Ut VIII4

SUMMARY AND CONCLUSIONS

The object of the research described in this report ia thepreparation and evaluation of fluorine-containing elastomers withvery wide useful temperature ranges and resistance to a widevariety of solvents, hydraulic fluids, lubricants, and otherliquids.

Polymers of 3(W -chloroperfluoroethoxy)l,l-dihydroperfluoro-propyl acrylate, (w-Cl-FEFPA) and copolymers with traces ofacrylic acid have been evaluated. Vulcanizates obtained with theamine cure have the low temperature flexibility characteristic ofthe other fluorine-containing alkoxy acrylates previously prepared.Resistance to aromatic solvents and 70:30 fuel is also comparable,but somewhat higher swelling is observed in oxygenated solvents.Resistance to dry heat is comparable but resistance to diesterlubricants, as well as tensile strengths, are somewhat inferior.Preparation of LO-Cl-FEFPA polymer does not look particularlyattractive relative to other fluorine-containing alkoxy acrylates.

Major effort was directed toward polymerization of 1,2-epoxyperfluoroheptane, C5FllCF -F 2 . Peroxide-catalyzed reactions

0at elevated temperatures gave fair conversions to products whichappear to be mainly the result of ring opening and rearrangement.The products contain little, if any, polymer.

Attempts to polymerize C5F l l CF F2 with FeCl 3 :propylene oxide-0

adducts led to fair yields of similar reaction products with littleevidence of polymer formation.

Attempts to copolymerize C5FllQF9F 2 and propylene oxide with0

certain FeC1 3 :propylene oxide adducts gave high conversions toproducts which appear to be copolymers. They are tan, viscousliquids. The molecular weights of the products are quite low andit has not yet been possible to prove that copolymerization oc-curred.

Preliminary attempts to copolymerize perfluoro-2-azapropene,CF3-N-CF 2 , with vinyl-type monomers have given low molecularweight products containing small amounts of the azapropene.

WADC TR 52-197 Pt VIII 15

APPENDIX

1. Emulsion recipe for fluorine-containing acrylates

Monomer 100 parts by weightWater 180Duponol ME 3Potassium persulfate 0.25

2. Amine Recipe

Polymer 100 parts by weightPhilblack 0 35Sulfur 1.0Triethylene tetramine 1.0

Cure: 30 minutes at 310'F.

WADC TR 52-197 Pt VIII 16