Synthesis of fluorinated amides

Details Synthesis of fluorinated amides Synthesis of fluorinated amides

2000-03-23

2001-02-13

Geist, Gary (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

Reexamination Certificate

active

06187954

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the preparation of fluorinated polyether amides, particularly the synthesis of perfluoropolyalkylethers having amide terminal groups. The invention has particular applicability to the preparation of fluorinated polyether amides which are useful as lubricants for magnetic recording medium.
BACKGROUND OF THE INVENTION
Fluoropolyether lubricants are of particular interest in lubricating magnetic recording media. These lubricants are uniquely suited to form lubricant topcoats on magnetic media because of such properties as chemical inertness, low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most typically used in forming topcoat lubricants on magnetic recording media.
Commercially available PFPE lubricants include Krytox from DuPont, Demnum from Daikin Industries and Fomblin Z and Y fluids from Montedison. Many of the commercial PEPE lubricants are substituted with 14 polar end-groups, such as one or more hydroxyl, or carboxylic acid groups. The polar end-groups are considered necessary to improve adhesion of the lubricants to the surface of a magnetic recording medium. Several fluorinated polyakylether amides have recently proven useful in forming lubricant topcoats on magnetic recording media
These lubricants can be conventionally prepared by combining an acid chloride with an amine. For example, U.S. Pat. No. 4,897,211 discloses the preparation of a synthetic magnetic recording lubricant by reacting a perfluoropolyalkylether acid chloride with an amine at elevated temperatures to produce the amide. This method, however, requires the use of air and moisture sensitive acid chlorides. Further, acid chlorides of fluoropolyether lubricants are not readily available, thus necessitating an additional step for their preparation prior to their reaction with the amine compound to form the amide.
Lower weight fluorinated compounds have also been used for the synthesis of lower weight fluorinated alkyl amides. See, e.g., U.S. Pat. Nos. 2,502,478 and 2,523,470 which are directed to the preparation of amide derivatives of tetrafluorosuccinic acid. These preparations, however, are not related to the synthesis of polymeric fluoroyalkylether amides and the products discloses therein are not useful as lubricants for magnetic recording media. Further, it is believed that the preparations used in synthesizing low weight amides are not amenable to preparing polymeric fluoropolyalkylether lubricants.
Other preparations of amides includes reacting fluorinated compounds with ammonia as in U.S. Pat. Nos. 2,862,024 and 3,544,618. These references disclose reaction conditions that require low temperatures to produce the amides. Further the disclosed compounds are not related to magnetic recording media lubricants such as fluoropolyalkylether amides.
The preparation of fluorinated amides as intermediates in the formation of nitrites have further been disclosed, as in U.S. Pat. Nos. 5,637,748 and 5,717,037. As discussed in the 5,637,748 patent to Hung, the solubility of fluorinated compounds are typically low, thus requiring special procedures and/or handling to achieve high yield products. It is believed that these difficulties are exacerbated when preparing high molecular weight compounds, such as polymeric fluoroalkylethers. Additionally, these references, as others in the art disclose that the preparation of the amides from ammonia require low temperatures.
Accordingly a continuing need exists in the magnetic lubrication art to produce fluoropolyalkylether derivatives in direct and economical means from commercially available products. In particular a need has been demonstrated to synthesize fluorinated amides useful in magnetic recording lubrication without the use of air sensitive intermediates and/or harsh reaction conditions.
SUMMARY OF THE INVENTION
An aspect of the present invention is a facile method of preparing a synthetic fluoropolyalkylether amide lubricant for a magnetic recording medium.
Additional aspects and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other aspects are achieved in part by a method of preparing a synthetic fluoropolyalkylether amide lubricant for a magnetic recording medium. The method comprises combing (i) a fluoropolyalkylether substituted with one or more ester end-groups and (ii) a primary or secondary amine. The reaction can advantageously be carried out under mild conditions, e.g., at a temperature of from about 15° C. to about 30° C. The method of the present invention further eliminates the use of acid chlorides, anhydrides and/or other air sensitive intermediates and elevated or low temperatures. In accordance with the present invention, the method of preparing a synthetic fluoropolyalkylether amide lubricant is advantageously carried out without the aid of a catalyst to form the fluoropolyalkylether amide.
Embodiments of the present invention include combining the fluoropolyalkylether substituted with one or more ester end-groups with the primary or secondary amine at a temperature of from about 20° C. to about 25° C. to form the fluoropolyalkylether amide.
In an embodiment of the present invention the product is a fluoropolyalkylether amide having the formula:
Rf—(CONR
1
R
2
)
q
wherein Rf is a fluoropolyalkylether;
R
1
and R
2
are independently substituted or unsubstituted alkyl or alkenyl groups; and q is 1-4.
The fluoropolyalkylether substituted with one or more ester end-groups has the formula:
Rf—(COOR′)
q
wherein Rf is a fluoropolyalkylether; R′ is a lower alkyl group and q is 1-4. The fluoropolyalkylether ester can be readily prepared by combining commercially available fluoropolyether carboxylic acids with an ortho ester, such as trimethyl or triethyl orthoformate.
Embodiments include fractionating the fluoropolyalkylether substituted with one or more ester end-groups to a polydispersity index of less than about 1.5 prior to combining the ester with the amine. In an embodiment of the present invention the fluoropolyalkylether ester has a number average molecular weight of about 4,000-20,000 a.m.u.
Additional advantages of the present invention will become readily apparent to those having ordinary skill in the art from the following detailed description, wherein the embodiments of the invention are described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
DESCRIPTION OF THE INVENTION
The present invention stems from the surprising discovery that certain fluoropolyether amide compounds can be prepared from their respective esters under mild reaction conditions, i.e., the reaction can be carried out at room temperature. A particularly advantageous aspect of the present invention is the ability to produce the fluoropolyether amides without the use of catalysts or additional acids or bases.
In practicing the invention, a synthetic fluoropolyalkylether amide lubricant for a magnetic recording medium, is prepared by combining a fluoropolyalkylether substituted with one or more ester end-groups with a primary or secondary amine. The reaction is carried out at about room temperature to form the fluoropolyalkylether amide, without the use of a catalyst. As used herein, a catalyst is a substance tha

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