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Claims  |
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What is claimed is:
1. A product comprising a silica gel or glass substrate to which is
chemically bonded a monolayer of silicon atoms which are connected to
other silicon atoms in said monolayer through oxygen atoms in said
monolayer, wherein the monolayer is substituted with first and second
hydrocarbyl substituents and each of the silicon atoms in said monolayer
is substituted with said first hydrocarbyl substituent or said second
hydrocarbyl substituent, wherein said first hydrocarbyl substituent is
longer than said second hydrocarbyl substituent, and wherein the density
of said hydrocarbyl substituents is at least 7 micromoles per square meter
of substrate surface,
wherein said product is formed by hydrating the surface of said substrate
to form on said surface a monolayer of water, and then reacting said
surface of said substrate with silanes of the formulas R.sup.1 SiX.sub.3
and R.sup.2 SiX.sub.3, wherein R.sup.1 and R.sup.2 are hydrocarbyl
substituents and X is a leaving group, provided that R.sup.1 is longer
than R.sup.2, under conditions under which said silanes react at said
surface and form said monolayer of silicon atoms.
2. The product of claim 1 wherein said first and second hydrocarbyl
substituents are distributed essentially uniformly on said substrate.
3. The product of claim 1 wherein said first hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group consisting of --0--, --N(R)--,
--S--, --C(O)--, --SO--, --C(O)O--, --OC(O)--, --C(O)N(R)--, or
--N(R)C(O)--; wherein the phenyl, alkyl, and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO,H, --N(R)(R),
straight or branched alkyl containing 1 to 6 carbon atoms, and --R.sup.1
Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1 and R.sup.2
are alkyl, alkoxy or alkylene containing up to 6 carbon atoms, and R in
each occurrence is hydrogen or alkyl containing 1 to 6 carbon atoms.
4. The product of claim 1 wherein said second hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO.sub.2 --, --C(O)O--, --OC(O)--, --C(O)N(R)--, and
--N(R)C(O)--; wherein the phenyl, alkyl and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
5. The product of claim 1 wherein the mole ratio of said first hydrocarbyl
substituent to said second hydrocarbyl substituent on said substrate is
100:1 to 1:100.
6. A product according to claim 1 wherein said first hydrocarbyl
substituent has the formula HOCH.sub.2 --CH(OH)CH.sub.2 --.
7. A product according to claim 1 wherein said substrate is bonded to the
silicon atoms in said monolayer through oxygen atoms.
8. A product according to claim 1 comprising silica gel to which is
chemically bonded a protective monolayer of silicon atoms which are
connected to other silicon atoms in said monolayer through oxygen atoms in
said monolayer, wherein the monolayer is substituted with first and second
hydrocarbyl substituents and each of the silicon atoms in said monolayer
is substituted with said first hydrocarbyl substituent or said second
hydrocarbyl substituent, wherein said first hydrocarbyl substituent is
longer than said second hydrocarbyl substituent.
9. The product of claim 8 wherein said first and second hydrocarbyl
substituents are distributed essentially uniformly on said substrate.
10. The product of claim 8 wherein said first hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group of consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO--, --C(O)O--, --OC(O)--, --C(O)N(R)--, and
--N(R)C(O)--; wherein the phenyl, alkyl and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3-n (OH).sub.n, wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
11. The product of claim 8 wherein said second hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene containing a
total of up to 60 carbon atoms and which contain one or more hetero
linkages selected from the group of consisting of --O--, --N(R)--, --S--,
--C(O)--, --SO--, --C(O)O--, --OC(O)--, --C(O)N(R)--, and --N(R)C(O)--;
wherein the phenyl, alkyl and alkylene are optionally substituted with one
or more substituents selected from the group consisting of hydroxyl,
halogen, cyano, nitro, --COOH, --SO.sub.3 H, --N(R)(R), straight or
branched alkyl containing 1 to 6 carbon atoms, and --R.sup.1
Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1 and R.sup.2
are alkyl, alkoxy or alkylene containing up to 6 carbon atoms, and R in
each occurrence is hydrogen or alkyl containing 1 to 6 carbon atoms.
12. The product of claim 8 wherein the mole ratio of said first hydrocarbyl
substituent to said second hydrocarbyl substituent on said substrate is
100:1 to 1:100.
13. The product of claim 8 wherein said first hydrocarbyl substituent
contains 2 to 24 carbon atoms.
14. The product of claim 8 wherein said second hydrocarbyl substituent
contains 1 to 6 carbon atoms.
15. The product of claim 8 wherein said first hydrocarbyl substituent is
octadecyl and said second hydrocarbyl substituent is propyl.
16. The product of claim 8 wherein said first hydrocarbyl substituent is
octadecyl and said second hydrocarbyl substituent is methyl.
17. The product of claim 8 wherein said first hydrocarbyl substituent is
octyl and said second hydrocarbyl substituent is methyl.
18. The product of claim 8 wherein said first hydrocarbyl substituent is
butyl and said second hydrocarbyl substituent is methyl.
19. The product of claim 8 wherein said first hydrocarbyl substituent
occupies about 20 to about 50% of the surface of said substrate.
20. The product of claim 8 wherein the mole ratio of said first hydrocarbyl
substituent to said second hydrocarbyl substituent is about 1:1 to about
1:4.
21. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 8.
22. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 9.
23. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 10.
24. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 11.
25. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 10.
26. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 13.
27. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 14.
28. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 15.
29. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 19.
30. In the method of chromatographically separating a mixture of substances
using a chromatographic material, the improvement wherein said material is
a product according to claim 20.
31. A product according to claim 1 comprising a glass surface to which is
chemically bonded a protective monolayer of silicon atoms which are
connected to other silicon atoms in said monolayer through oxygen atoms in
said monolayer, wherein the monolayer is substituted with first and second
hydrocarbyl substituents and each of the silicon atoms in said monolayer
is substituted with a first hydrocarbyl substituent or a second
hydrocarbyl substituent, wherein said first hydrocarbyl substituent is
longer than said second hydrocarbyl substituent.
32. The product of claim 31 wherein said first and second hydrocarbyl
substituents are distributed essentially uniformly on said substrate.
33. The product of claim 31 wherein said first hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group of consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO.sub.2 --, --C(O)O--, --OC(O)--, --C(O)N(R)--, and
--N(R)C(O)--; wherein the phenyl, alkyl and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3--n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
34. The product of claim 31 wherein said second hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene containing a
total of up to 60 carbon atoms and which contain one or more hetero
linkages selected from the group of consisting of --O--, --N(R)--, --S',
--C(O)--, --SO--, --C(O)O--, --OC(O)--, --C(O)N(R)--, and --N(R)C(O)--;
wherein the phenyl, alkyl and alkylene are optionally substituted with one
or more substituents selected from the group consisting of hydroxyl,
halogen, cyano, nitro, --COOH, --SO.sub.3 H, --N(R)(R), straight or
branched alkyl containing 1 to 6 carbon atoms, and --R.sup.1
Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1 and R.sup.2
are alkyl, alkoxy or alkylene containing up to 6 carbon atoms, and R in
each occurrence is hydrogen or alkyl containing 1 to 6 carbon atoms.
35. The product of claim 31 wherein the mole ratio of said first
hydrocarbyl substituent to said second hydrocarbyl substituent on said
substrate is 100:1 to 1:100.
36. The product of claim 31 wherein said first hydrocarbyl substituent
contains 2 to 24 carbon atoms.
37. The product of claim 31 wherein said second hydrocarbyl substituent
contains 1 to 6 carbon atoms.
38. The product of claim 31 wherein said first hydrocarbyl substituent is
octadecyl and said second hydrocarbyl substituent is propyl.
39. The product of claim 38 wherein said first hydrocarbyl substituent
occupies about 20 to about 50% of the surface of said substrate.
40. The product of claim 31 wherein the mole ratio of said first
hydrocarbyl substituent to said second hydrocarbyl substituent is about
1:1 to about 1:4.
41. The method of rendering a silica gel or glass surface resistant to
chemical and mechanical degradation which comprises forming on said
surface a protective monolayer of silicon atoms which are connected to
other silicon atoms in said monolayer through oxygen atoms in said
monolayer, wherein the monolayer is substituted with first and second
hydrocarbyl substituents and each of the silicon atoms in said monolayer
is substituted with a first hydrocarbyl substituent or a second
hydrocarbyl substituent, wherein said first hydrocarbyl substituent is
longer than said second hydrocarbyl substituent, and wherein the density
of said hydrocarbyl substituents is at least 7 micromoles per square meter
of substrate surface;
wherein said protective monolayer is formed hydrating the surface of said
substrate to form on said surface a monolayer of water, and then reacting
said surface of said substrate with silanes of the formulas R.sup.1
SiX.sub.3 and R.sub.2 SiX.sub.3, wherein R.sup.1 and R.sup.2 are
hydrocarbyl substituents and X is a leaving group, provided that R.sup.1
is longer than R.sup.2, under conditions whereunder said silanes react at
said surface and form said monolayer of silicon atoms.
42. The method of claim 41 wherein said first hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO.sub.2 --, --C(O)O--, --OC(O)--, --C(O)N(R)--, or
--N(R)C(O)--; wherein the phenyl, alkyl, and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sub.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
43. The method of claim 41 wherein said second hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide and derivatives of alkyl or monounsaturated alkylene which contain
a total of up to 60 carbon atoms and which contain one or more hetero
linkages selected from the group consisting of --O--, --N(R)--, --S--,
--C(O)--, --SO.sub.2 --, --C(O)O--, --OC(O)--, --C(O)N(R)--, and
--N(R)C(O)--; wherein the phenyl, alkyl and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
44. The method according to claim 41 wherein material having a glass
surface is rendered resistant to chemical and mechanical degradation of
said surface.
45. The method of claim 44 wherein said first hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO--, --C(O)O--, --OC(O)--, --C(O)N(R)--, or
--N(R)C(O)--; wherein the phenyl, alkyl, and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
46. The method of claim 44 wherein said second hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO.sub.2 --, --C(O)O--, --OC(O)--, --C(O)N(R)--, and
--N(R)C(O)--; wherein the phenyl, alkyl and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
47. The method of claim 44 wherein said material is selected from the group
consisting of glassware, optical fiber, and capillaries.
48. The method of claim 47 wherein said material is a fiber optic filament.
49. The method of claim 41 wherein material having a silica gel surface is
rendered resistant to chemical and physical degradation of said surface.
50. The method of claim 49 wherein said first hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide and derivatives of alkyl or monounsaturated alkylene which contain
a total of up to 60 carbon atoms and which contain one or more hetero
linkages selected from the group consisting of --O--, --N(R)--, --S--,
--C(O)--, --SO.sub.2, --C(O)O--, --OC(O)--, --C(O)N(R)--, or --N(R)C(O)--;
wherein the phenyl, alkyl, and alkylene are optionally substituted with
one or more substituents selected from the group consisting of hydroxyl,
halogen, cyano, nitro, --COOH, --SO.sub.3 H, --N(R)(R), straight or
branched alkyl containing 1 to 6 carbon atoms, and --R.sup.1
Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1 and R.sup.2
are alkyl, alkoxy or alkylene containing up to 6 carbon atoms, and R in
each occurrence is hydrogen or alkyl containing 1 to 6 carbon atoms, and R
in each occurrence is hydrogen or alkyl containing 1 to 6 carbon atoms.
51. The method of claim 49 wherein said second hydrocarbyl substituent is
selected from the group consisting of phenyl, alkyl containing 1 to 60
carbon atoms, monounsaturated alkylene containing 2 to 60 carbon atoms,
epoxide, and derivatives of alkyl or monounsaturated alkylene which
contain a total of up to 60 carbon atoms and which contain one or more
hetero linkages selected from the group consisting of --O--, --N(R)--,
--S--, --C(O)--, --SO.sub.2 --, --C(O)O--, --OC(O)--, --C(O)N(R)--, and
--N(R)C(O)--; wherein the phenyl, alkyl and alkylene are optionally
substituted with one or more substituents selected from the group
consisting of hydroxyl, halogen, cyano, nitro, --COOH, --SO.sub.3 H,
--N(R)(R), straight or branched alkyl containing 1 to 6 carbon atoms, and
--R.sup.1 Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, R.sup.1
and R.sup.2 are alkyl, alkoxy or alkylene containing up to 6 carbon atoms,
and R in each occurrence is hydrogen or alkyl containing 1 to 6 carbon
atoms.
52. A method for treating the surface of an article having a surface of
silica gel or glass comprising hydrating said surface to form thereon a
monolayer of water, and then reacting said surface with silanes of the
formula R.sup.1 SiX.sub.3 and R.sup.2 SiX.sub.3, wherein R.sup.1 and
R.sup.2 are hydrocarbyl substituents and X is a leaving group, provided
that R.sup.1 is longer than R.sup.2, under conditions whereunder said
silanes react at said surface and form a monolayer of silicon atoms
chemically bonded to said surface which silicon atoms are connected to
other silicon atoms in said monolayer through oxygen atoms in said
monolayer, wherein each of said silicon atoms in said monolayer is
substituted with R.sup.1 or R.sup.2 and wherein the density of said
hydrocarbyl substituents in said monolayer is at least 7 micromoles per
square meter of substrate surface.
53. The method according to claim 52 which comprises contacting said
surface with said silanes in a solution of said silanes.
54. The method according to claim 52 which comprises contacting said
surface of said article with a gas comprising said silanes.
55. A method according to claim 54 wherein said article is a fiber optic
filament, the method comprising drawing said filament through said gas
under conditions whereunder said silanes react with the surface of said
filament. |
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Claims |
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Description |
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The present invention relates to providing specialized polysiloxane
coatings to articles. The coatings provide protective attributes to the
substrates bearing the coatings, without loss of and in some cases with
enhancement of the desirable properties of the substrates.
The present invention relates in particular to the formation of specialized
siloxane monolayers on substrates which are susceptible to damage upon
exposure to acidic environments or basic environments, or which are
vulnerable to physical degradation such as cracking. The invention relates
in particular to the provision of such monolayers on silica-based
chromatographic supports, in order to protect such supports from damage
due to the ambient chemical environment while retaining the desirable
chromatographic properties of the support. The invention also relates to
providing such monolayers to glassware and glass surfaces, to provide
desired protection as described hereinbelow.
While it has generally been known to apply "silicone" coatings to articles
to impart various protective properties, such as waterproofing, it is
believed herein to be novel to adjust the substituents on the silicon
atoms making up such coatings in order to favorably affect the properties
of the coating and of the articles bearing the coating. In addition,
providing such adjustment on "coatings" which are in reality monolayers of
siloxanyl (that is, --Si--O--) based monolayers is believed to be all the
more novel.
Chromatographic packings can comprise silica gel to which organic
substituents, such as alkyl chains, have been attached. It has heretofore
been accepted that the susceptibility of such materials to attack by acids
or bases has been an unavoidable concomitant of the packing's ability to
perform properly in chromatographic applications. Thus, modification such
as that which is the subject of the present invention has not been
considered.
Indeed, formation of a siloxanyl monolayer might be expected to interfere
with properties such as chromatographic capabilities because it would
alter the shape and size of pores and would affect other surface
characteristics.
For instance, a published abstract with respect to Japanese Patent
Application No. 61287444 describes porous silica particles characterized
in that the inner surfaces of the pores carry a hydrophobic layer formed
by a reaction of the silica in the pore with an alkyl or aryl halosilane,
among which are listed octadecyltri-chlorosilane and
propyltrichlorosilane, among others, wherein the remaining exposed surface
of the silica particle is bonded to hydrophilic groups such as ethylene
glycol, glycerol, sorbitol, polyethylene oxide,
glycidoxypropyltrimethoxy-silane, ethyleneglycolmono-ethylether, or
diethyleneglycol. The abstract does not disclose the formation of a
siloxanyl monolayer, nor is there disclosed any intimate intermingling of
different substituents on adjacent silicon atoms; indeed, such a product
would be directly contrary to the teachings of this abstract which
requires substituents of various types at quite distinct locations on the
silica particle.
A number of other sources disclose bonding various substituents to an oxide
surface, particularly a silica surface, but none discloses or suggests
providing multiple distinct substituents at adjacent or nearly adjacent
sites on a siloxanyl monolayer. Examples wherein the substrate is glass or
a chromatographic surface include U.S. Defensive Publication T958,010,
U.S. Pat. Nos. 4,755,294, 4,604,207, and 4,512,898. Other publications
examining the formation of alkyl-substituted siloxanyl monolayers on
silica gel are typified by P. Silberzan, et al., in Langmuir, Vol. 7, No.
8, pp. 1647-1651 (1991) and S. Wasserman, et al., in J. Am. Chem. Soc.,
Vol. 111, No. 15, pp. 5852-5861 (1989).
Briefly stated, one aspect of the present invention is a product to which
is chemically bonded a monolayer of silicon atoms which are connected to
other silicon atoms in said monolayer through oxygen atoms in said
monolayer, wherein the monolayer is substituted with a first hydrocarbyl
substituent and a second hydrocarbyl substituent and each of the silicon
atoms in said monolayer is substituted with said first hydrocarbyl
substituent or said second hydrocarbyl substituent, wherein said first
hydrocarbyl substituent is longer than said second hydrocarbyl
substituent.
In another aspect of the present invention, the product is silica gel or
another inorganic oxide, or a substrate whose surface is silica gel or
such other inorganic oxide, and the first and second hydrocarbyl
substituents are selected such that the substrate bearing the substituted
monolayer is useful as, for instance, a chromatography column, and
exhibits a high degree of resistance to acidic and basic attack. Yet
another aspect of the present invention is the use of such a product in
chromatography.
Yet another aspect of the present invention is glass, such as glass
articles, glassware, glass optical fibers, glass capillaries, and the
like, bearing the monolayer described herein, wherein the monolayer
protects the surface of the glass from acidic and basic environments and
from physical degradation such as cracking.
While the present invention is particularly useful in the preparation of
products comprising silica which bears the monolayer described herein, the
present invention is believed to be useful in providing the indicated
protection against chemical degradation to a large variety of materials.
Stated generally, any product having a surface which reacts with alkyl
trichlorosilane to bond to the silane, can be provided with a monolayer in
accordance with the present invention. Preferred materials are
characterized in that they comprise surface oxygen. By "surface oxygen" is
meant that the material contains, at its surface, oxygen which is
covalently (or, in certain embodiments, ionically) bound in the material,
which oxygen is capable of being covalently bonded to silanes. More
specifically, the surface oxygen is considered within the scope of this
aspect of the invention if the oxygen reacts with any alkyl
trichloro-silane to form O--Si bonds.
Preferred materials to which the monolayer is applied include silica gel,
silica-based glass and glassware, and optical "fiber optic" cable, as well
as materials comprising oxides or mixed oxides of any inorganic material
whose oxide is solid at standard temperature and pressure. Also included
are carbonates, aluminosilicates, silicates and phosphates, of any
inorganic cation. Also included are materials in which two or more of
these are chemically combined or physically blended. Examples of the
foregoing include inorganic pigments, limestone and clays (which typically
comprise aluminosilicates). Additional examples include any inorganic
element and oxides thereof so long as the surface thereof is capable of
forming bonds to silicon atoms in the monolayer. Examples include but are
not limited to alumina, zirconia, beryllia, titanium dioxide, magnesium
oxide, and oxides of vanadium, chromium, manganese, iron, cobalt, nickel,
copper, zinc, gadolinium, germanium, arsenic, rubidium, strontium,
yttrium, niobium, molybdenum, ruthenium, rhodium, platinum, gold, silver,
thallium, lead and bismuth.
One preferred embodiment of the present invention is silica gel or a
substrate of a different material having a silica gel surface. The
monolayer provides a protective layer to the silica gel.
The invention finds particular usefulness in chromatographic applications,
including not only silica-based chromatographic supports but also
metal-oxide chromatographic substrates.
Another preferred embodiment of the present invention is glass articles,
such as glassware, capillary tubes, optical fibers, windows and
windshields (whether for conventional construction and vehicular
applications or more specialized uses in reactors and spacecraft), and any
other article having a glass outer and/or inner surface. Providing the
monolayer to glassware will help protect against acidic and basic
environments, and will help resist the microscopic chemical and mechanical
processes at the glass surface that help initiate and propagate cracking
and related degradation. Providing the monolayer to optical fibers and
inner spaces such as capillaries will likewise protect the inertness of
the glass surface to acidic and basic attack and to mechanical
degradation. Capillary tubes thus treated are useful in capillary
chromatography and capillary electrophoresis.
Of particular interest is the embodiment wherein a surface comprising
zirconium oxide (per se or alloyed) is treated in accordance with the
present invention to provide protection from the aggressive environment to
which the zirconium-based materials are exposed when they are used as
moderators in pressured-water nuclear power reactors. Preferred groups to
provide on such an oxidic surface are lower alkyl, such as methyl, and
di-dydroxy lower alkyl, such as HOCH.sub.2 --CH(OH)--CH.sub.2 --.
As indicated, the monolayer is formed of silicon atoms bound to the
substrate surface and connected to each other through single oxygen atoms.
In addition, the monolayer is characterized in that it is substituted with
the first and second hydrocarbyl substituents described herein. Each of
the silicon atoms forming the monolayer is substituted with either a first
hydrocarbyl substituent or a second hydrocarbyl substituent. In the
broadest aspect of the present invention, there may be regions of the
monolayer in which the first hydrocarbyl substituent predominates, even to
the exclusion of the second hydrocarbyl substituent, and vice versa.
However, in the preferred embodiment the first and second hydrocarbyl
substituents are both distributed essentially uniformly across the surface
of the monolayer. While it will be recognized that totally unvarying
distribution of the first and second substituents on the monolayer may not
be achieved, the product will generally preferably be characterized in
that each of the first and second substituents are distributed essentially
uniformly, or as nearly uniformly as possible, on the surface of the
monolayer. In that way, the relative proportions of the first and second
substituents will be essentially constant at any region on the monolayer.
The first and second hydrocarbyl substituents are preferably selected to
optimize the property or properties desired of the product which will bear
the monolayer, and to ensure the provision of a protective coating to the
surface of the article. In the aspect of the present invention in which
the desired property is the ability to carry out effective chromatographic
separation when the article is used as a packing material for, e.g., HPLC
or other gas-phase chromatography, the first hydrocarbyl substituent
should be one which assists in providing chromatographic separation when
bound to a chromatographic support. Examples of such substituents will be
familiar to those conversant with the field of chromatography, and are
indeed quite numerous. Examples include phenyl; epoxide; alkyl, containing
from 1 to 60 carbon atoms in the longest chain, preferably 1 to 30 and
more preferably 3 to 18 atoms in the longest chain; monounsaturated
alkylene containing 2 to 60 carbon atoms in the longest chain; or
derivatives in which alkyl or monounsaturated alkylene containing up to 60
carbon atoms contains one or more (preferably up to 12) hetero linkages
such as --O--, --N(R)--, --S--, --C(O)--, --SO.sub.2 --, --C(O)O--,
--OC(O)--, --C(O)N(R)--, or --N(R)C(O)--. The phenyl, alkyl and alkylene
may optionally be substituted with one or more of hydroxyl, halogen
(particularly fluorine, chlorine or bromine, especially fluorocarbons),
cyano, nitro, --COOH, --SO.sub.3 H, --N(R)(R), --R.sup.1
Si(R.sup.2).sub.3-n (OH).sub.n wherein n is 1, 2 or 3, wherein R.sup.1 and
R.sup.2 are each alkyl, alkoxy or alkylene containing up to 6 carbon
atoms, and preferably methyl, ethyl, methoxy or ethoxy; or straight or
branched lower alkyl containing up to 6 carbon atoms (which lower alkyl
may be substituted with any of the foregoing substituents), wherein R at
each occurrence is hydrogen or alkyl containing 1 to 6 carbon atoms. Thus,
--N(R)(R) can be amino, monoaklylamino, or dialkylamino. Thus, exemplary
functional groups include diol (such as HOCH.sub.2 --CH(OH)CH.sub.2 --),
polyamine, carboxylic acid, sulfonic acid, and (N-trimethoxysilylpropyl)
polyethyleneimine.
A preferred first substituent is alkyl containing 2 to 24 carbon atoms, and
more preferably octadecyl. Preferred embodiments in which the alkyl chain
has a substituent are those in which the substituent is in the
omega-position. Another preferred first hydrocarbyl substituent has
terminal ethylenic unsaturation. Examples include CH.sub.2 .dbd.CHCH.sub.2
--, and more generally CH.sub.2 .dbd.CH--(CH.sub.2).sub.1-24 --. The
unsaturated group is useful in that other molecules that react with
-CH.dbd.CH.sub.2 groups can be attached to the hydrocarbyl substituent at
that site. Epoxide groups and hydride groups, when present attached to the
hydrocarbyl substituents, can also serve as sites to which other molecules
and functional groups can be attached. Examples of such molecules include
ones that impart hydro-phobicity or color, or which serve as cladding for
the surface of a glass filament fiber optic transmission line. Examples of
the latter include C.sub.1 -C.sub.6 acrylates and methacrylates.
The second hydrocarbyl substituent can also be any of the foregoing
substituents, provided that the second hydrocarbyl substituent is shorter
than the first hydrocarbyl substituent. Preferably, for chromatographic
applications, the second hydrocarbyl substituent is sufficiently shorter
than the first such that a chromatographic support prepared in accordance
with the present invention having a given first hydrocarbyl substituent is
essentially undistinguishable in its chromatographic properties from a
conventional silica gel support to which is grafted the same given first
hydrocarbyl substituent. When the first substituent is C.sub.12 -C.sub.24
alkyl, the second substituent is preferably alkyl containing 1 to 6 carbon
atoms and more preferably propyl. When the first hydrocarbyl substituent
is relatively short, i.e., alkyl containing up to 6 carbon atoms, or
phenyl, the second hydrocarbyl substituent is preferably a shorter alkyl
chain (optionally substituted as described above) or may simply be
hydrogen.
In applications of the present invention other than the preparation of
chromatography supports, the first and second hydrocarbyl substituents can
be chosen as appropriate to provide any other desired properties such as
abrasion resistance, translucency, transparency, refractive index, light
reflectivity (e.g., outside a fiber optic line), hydrophilicity,
hydrophobicity, or rheology (for instance, of treated minerals or pigments
in an emulsion or in an aqueous or non-aqueous liquid preparation). In all
events, the monolayer prepared in accordance with the present invention
will impart the product with the desired ability to resist chemical
degradation in acidic and basic environments. The second hydrocarbyl
substituent is preferably one which maximizes the ability of the monolayer
to prevent penetration of acidic and basic substances and ions to the
product surface. Preferred second hydrocarbyl substituents are thus alkyl
groups containing up to 6 carbon atoms, optionally substituted with
halogen (particularly fluorine) or with C.sub.1-3 alkyl.
The relative amounts of the first and second hydrocarbyl substituents on
the monolayer are readily adjustable, and should be selected to provide
the desired properties of the product bearing the monolayer. For instance,
for chromatographic applications it is generally preferred that the
density of the first hydrocarbyl substituent be about 2 to about 3
micromoles per square meter of silica gel surface, which corresponds to
about 20 percent to about 50 percent of the surface. This permits the
second hydrocarbyl substituent to "space" the longer substituents from
each other while still retaining the desired protection to the substrate
and the desired chromatographic properties. Accordingly, the mole ratio of
first hydrocarbyl substituent to the second hydrocarbyl substituent on the
substrate when it is to be used as a chromatographic material will
preferably comprise about 1:1 to about 1:4. It will be recognized that,
depending on the property or properties desired, the mole ratio of the
first hydrocarbyl substituent to the second hydrocarbyl substituent can
range from as low as below 1:100 to as high as 100:1, or higher, although
the beneficial effects of the second hydrocarbyl substituent "spacing" the
first hydrocarbyl substituents from each other are less pronounced as the
ratio of first to second hydrocarbyl substituents exceeds about 1:1.
As set forth more fully hereinbelow, the relative ratios of the reactants
employed to form the desired monolayer have to be adjusted so as to
provide the desired ratio of substituents on the monolayer, taking into
account the fact that the reactants will usually react with the substrate
at different rates. For instance, a smaller reactant such as
propyltrichloro-silane reacts more quickly (and thus more of it reacts in
a given period of time) than n-octadecyltri-chlorosilane. Thus, because of
the differing reaction kinetics of each reactant, the ratio of one to
another before reaction will usually not equal the ratio of one to another
on the monolayer following reaction. The determination of the relative
amounts of each reactant to use, in order to obtain a given ratio of chain
lengths on the monolayer, is a straightforward matter for any particular
choice of substrate and hydrocarbyl substituents.
Preparation of articles bearing the monolayers described herein is
straightforward. The article having surface oxygen is preferably treated
to remove extraneous materials which might interfere with the bonding of
the silane reagent to the available oxygen. The surface of the article
needs to be hydrated, as free water is essential to achieving the desired
reaction between the silane and the surface oxygen. However, the surface
need not and should not carry liquid water in amounts that would interfere
with the desired interaction between the silane and the surface oxygen.
It has been determined that the amount of water present on the substrate
surface affects the hydrocarbyl group density that is obtained upon the
ensuing reaction, and that excessive amounts of reagent water lead to
decreased hydrocarbyl substituent density. Accordingly, it is highly
preferred that the amount of water present at the surface be that which
affords the densities of 7 or greater, and more preferably 8 or greater,
micromoles of hydrocarbyl substituents per square meter of substrate
surface. That amount of water is generally about equal to the amount (on a
mole basis) required by the silane reagents employed to form the
monolayer. Adequate hydration can be provided by cleaning and drying the
surface of the article to be treated and then exposing it to a humid
atmosphere so as to allow a surface monolayer of water vapor to form on
the article. Alternatively, adequate hydration can be provided by adding a
known, pre-calculated amount of water to a polar solvent in which the
hydrocarbyl substituents are provided to the reaction site.
One technique for applying the monolayer employs reactants in a liquid
phase. According to this procedure, a solution of silanes of the formula
R.sup.1 SiX.sub.3 and R.sup.2 SiX.sub.3 is formed in a solvent which is
inert to both of these silanes and to the article with which the reaction
will be carried out. In the foregoing formulas, R.sup.1 is the first
hydrocarbyl substituent, R.sup.2 is the second hydrocarbyl substituent and
X is a leaving group which is preferably chlorine, methoxy, or ethoxy. (If
the second hydrocarbyl desired is hydrogen, the corresponding reactant is
SiHCl.sub.3.) Suitable solvents include alkanes which are liquid at room
temperature and atmospheric pressure, such as n-hexadecane. The solvent is
preferably scrupulously anhydrous, to prevent premature reaction of the
silane with any trace amounts of water.
Then, the solution is applied to the surface on which formation of the
monolayer is desired. Depending on the nature and size of the article, it
can simply be immersed in the solution under a suitable inert gas blanket
to ensure that no atmospheric water vapor interferes with the desired
interaction between the article, the reagent surface water, and the
silanes. No special catalysts or extreme reaction conditions need be
observed; the silanation reaction generally proceeds to completion in a
matter of hours. In general, it can be expected that slightly raising the
temperature of the reaction mixture will accelerate the completion of the
reaction. The progress of the reaction can be followed in any of a number
of conventional ways, for instance by monitoring the formation of HX in
the solution; when the concentration of HX stops increasing, the
consumption of the silane has ceased.
Following the completion of the reaction, the thus treated material is
removed from the solution, washed, and dried. It can then be handled and
treated in accordance with techniques currently employed with analogous
materials to which the monolayer has not been applied in accordance with
this invention. For instance, silica gel treated in this manner can be
incorporated into an appropriate column to permit its use as a
chromatographic packing material. Then, any mixture desired to be treated
or analyzed chromatographically is simply applied to the column in a
wholly conventional manner.
The monolayer can also be applied in the vapor phase. The surface to be
treated (following surface cleaning, as described above) is contacted with
a vapor which comprises the silanes of the formula R.sup.1 SiX.sub.3 and
R.sup.2 SiX.sub.3, wherein R.sup.1, R.sup.2 and X are as defined above.
The vapor may consist entirely of these silanes, or it may contain, in
addition to those silanes, any other reagent intended to be reacted with
the substrate surface; and the vapor should contain sufficient reagent
water vapor in appropriate relative amounts as described herein to provide
the desired high density of hydrocarbyl group coverage. Also, the vapor
may contain as well diluents or carrier gas components which will not
react with the silanes nor with the surface. The vapor should be free of
components which, if present, would undesirably react with the surface and
interfere with the formation of the desired surface layer.
The silanes can be applied by placing the substrate in a chamber containing
the silanes. Alternatively, for a substrate such as a fiber optic
filament, the fiber can be drawn through such a chamber under conditions
providing sufficient temperature, circulation of the silanes, and
residence time in the chamber, such that the desired reaction at the
substrate surface occurs. Such an application technique permits faster
treatment times than applications from a liquid, because there is much
less residual drag than is inherent in drawing a fiber through a liquid.
This technique also permits incorporation of other components that would
also be desirably applied to the surface. The vapor-phase reaction is
preferably carried out at temperatures of about 100.degree. C. to
140.degree. C.
One advantage of the invention is thus that the chain length densities can
be arbitrarily varied, depending on the final product and properties
desired. Another advantage is that the final product exhibits no, or a
reduced number, of residual geminal silanols (i.e. silicon with two
hydroxyl groups).
When the treated material is a mineral or pigment, it can be subdivided and
added into other desired compositions such as paints, cosmetic
preparations, and the like.
It has also been determined that the hydrolytic stability of monolayers
applied in accordance with this invention can be | | |
