Porous materials having a dual surface

Porous materials having a dual surface are disclosed. Also disclosed is a method for their preparation. An example of such a material is a silica gel reacted with a reactive silane intermediate such as (CH.sub.3).sub.2 Si.dbd.O and then, with a reactive silane such as ##STR1## to give a dual treated material having --((CH.sub.3).sub.2 SiO).sub.x H on the exterior surface and ##STR2## on the interior surface of the pores.

BACKGROUND OF THE INVENTION 
According to Plueddemann, in the chapter on silylating agents in 
"Encyclopedia of Chemical Technology", 3rd edition, volume 20, page 962 et 
seq., silylation is the displacement of active hydrogen from an organic 
molecule by a silyl group. Plueddemann further states that "The active 
hydrogen is usually OH, NH, or SH, and the silylating agent is usually a 
trimethylsilyl halide or a nitrogen-functional compound. A mixture of 
silylating agents may be used; a mixture of trimethylchlorosilane and 
hexamethyldisilazane is more reactive than either reagent alone, and the 
by-products combine to form neutral ammonium chloride." 
Thus, what Plueddemann has described is what those skilled in the art 
regard as the "normal way" to silylate organic molecules using reactive 
silanes. 
It has been beneficial to industry to have this approach available to alter 
organic molecules to achieve certain new molecules. Those skilled in the 
art have extrapolated silylation of organic molecules to silylation of 
inorganic molecules as well. For example, it is known that silicas, used 
as fillers for compounded rubbers, could be treated with reactive silanes 
such as trimethylchlorosilane and/or hexamethyldisilazane to place 
trimethylsilyl groups on the surface of such silicas. This treatment 
arises through the reaction of the hydroxyls on the surface of the silica, 
with the reactive silanes. See, for example, Hertl, W. and Hair, M. L., 
"Reaction of Hexamethyldisilazane with Silica", J. of Phys. Chem., Volume 
75, No. 14, 1971 and Chmieloweic, J. and Marrow, B. A., "Alkylation of 
Silica Surfaces", J. of Coll. and Inter. Sci., Volume 94, No. 2, August 
1983 and Boksanyi, L., Liardon, O. and Kovats, E., Advances in Coll. and 
Inter. Sci., 6 (1976), pages 95 to 137. 
Particulate support materials used in liquid chromatography applications 
also benefit by silylation techniques. It is common in this art to use 
reactive silanes to treat the particulate materials to cover up reactive 
hydroxyl groups to improve the chromatographic properties of polar 
molecules. See, for example, L. R. Snyder and J. J. Kirkland, Introduction 
to Modern Liquid Chromatography, 2nd edition, Wiley Interscience, N.Y. 
1979. 
A more significant advance in the silylation art came about by the use of 
reactive silanes, which also contained organofunctional groups, to 
silylate surfaces. The desired result was to create a material having a 
novel end-use which was dependent on the type of organofunctional group 
included in the silylating silane. For example, in U.S. Pat. No. 
4,379,931, issued on Apr. 12, 1983, Plueddemann used unique reactive 
silanes, for example 
##STR3## 
to treat various particulate materials which were then used to extract 
metal ions from solution. 
For most of the practical applications known in the prior art, the 
preferred form of silylation is that which is carried out in solution. 
There are, however, some silylation applications wherein the silylation 
reaction is carried out in the vapor phase. It can be concluded therefore 
that it is generally known in the art to use various reactive silanes to 
react with hydroxyls on the surfaces of various materials. 
THE INVENTION 
What is disclosed in this invention is the use of reactive silane 
intermediatss to react with the hydroxyls on the exterior surfaces of 
porous materials and then the use of reactive silanes to react with the 
hydroxyls on the interior pore surface of the porous materials to provide 
a dual surface material in the sense that the silicon-containing groups 
attached to the exterior surface are different than the silicon-containing 
groups on the interior surface of the porous material. 
Further, it is contemplated that the silicon-containing groups covalently 
bonded to the exterior surface of the porous material will be 
predominantly those obtained from the reactive silane intermediate while 
the silicon-containing groups covalently bonded to the interior surface of 
the porous material will be predominantly those obtained from the reactive 
silanes. 
It is believed by the inventors herein that such dual surface materials are 
unique, having never been disclosed anywhere in the published literature. 
Such dual surface materials may be prepared by selecting dual groups that 
independently adjust transport properties to, and chemical activities of, 
such dual surface materials. 
Thus, it is an object of this invention to provide a process for preparing 
a composition having a dual surface, the processing comprising (I) 
contacting a porous material with a highly reactive silane intermediate 
capable of forming covalent bonds with hydroxyl groups on the exterior 
surface of the porous material; (II) allowing the mixture from (I) to 
react, thereby treating the porous material surface; (III) thereafter, 
contacting and mixing the treated porous material from (II) with a 
reactive silane, or its hydrolysis product, for a period of time to allow 
the reactive silane, or its hydrolysis product, to diffuse into the 
interior of the porous material and covalently bond with hydroxyl groups 
on the interior surface of the porous material; and (IV) subsequently 
isolating the dual surface porous material from the mixture of (III). 
It is a further object of this invention to provide a composition of matter 
consisting of a porous material having reacted to its exterior surface, 
silanol-containing groups which are not silica silanols, and having 
reacted to the surface of its porous interior, silicon- containing groups 
which are different from those reacted to the exterior surface. 
Thus, the ultimate goal of this invention is to provide a process which 
will give a composition that has a dual surface. What is meant by "dual 
surface" for purposes of this invention, is that the silicon-containing 
groups reacted to the exterior surface of the porous material are 
different in nature than the silicon-containing groups reacted to the 
surface of the porous interior of the porous materials. 
This goal can be achieved by first reacting the porous material with a 
small amount of a highly reactive silane intermediate to treat the 
exterior surface of the porous material with little or no diffusion into 
the pores and therefore, little or no treatment within the pores by the 
highly reactive silane intermediate, and then, reacting the so-treated 
porous material with an excess of a reactive silane and allowing the 
reactive silane, or its hydrolysis product, to diffuse into the pores and 
covalently bond to the interior surface. 
The major factor that allows the inventive process to produce the inventive 
compositions herein is that the reactive silane intermediates react very 
rapidly with the exterior surface hydroxyl and therefore, their physical 
entry into the pores is severely limited. Additional assistance to 
prevention of interior reaction is provided by adsorbed water, when 
present. Even if some of the reactive silane intermediate should reach the 
interior of the pore before reacting with the exterior surface hydroxyls, 
it is thought by the inventors that when some physisorbed water is present 
in the pores, the reactive silane intermediate immediately contacts water 
in the pores with which it reacts to form disilanols, e.g. (R).sub.2 
Si:+HOH.fwdarw.(R).sub.2 Si(OH).sub.2 and thus the reactive silane 
intermediate is prevented from reaching the hydroxyl groups that are 
situated deep in the interior surface of the pores. Moreover, any newly 
formed reactive silane intermediate that reaches any pore interior that 
has previously been the site of the (R).sub.2 Si:+HOH reaction, will 
immediately encounter the previously formed (R).sub.2 Si(OH).sub.2 which 
acts as an additional reaction site to react preferentially with the 
(R).sub.2 Si: to form dimers and other oligomers. A second benefit of 
adsorbed water is that when present, it can reduce the amount of the 
reactive silane intermediate precursor that resides in the pores. Hence, 
the reactive silane intermediate is effectively blocked from the interior 
of the pores. 
In this inventive method then, the first phase of the process requires two 
steps. The first step, i.e. step (I), requires contacting a porous 
material with a highly reactive silane intermediate and step (II) requires 
allowing the highly reactive silane intermediate to react with the porous 
material to obtain a "treated" porous material. It should be obvious to 
those skilled in the art that steps (I) and (II) can be carried out 
simultaneously. Step (III) is then carried out by contacting the "treated" 
porous material with a reactive silane and allowing the reactive silane, 
or its hydrolysis product, to diffuse into the pores and react with the 
hydroxyl therein. Subsequently, the desired end-product is isolated from 
the reaction mixture by some means. 
For purposes of this invention, in steps (I) and (II), the highly reactive 
silane intermediates are those that are known in the art. Such highly 
reactive silane intermediates are selected from a group consisting of 
silenes, silylenes and silanones. 
The first group of highly reactive silane intermediates, the silenes are 
highly unstable organosilicon compounds derived from precursor silanes by 
various means to be described infra. Their general structure is notable 
owing to the presence of a single silicon to carbon double bond, i.e. 
&gt;Si.dbd.CH.sub.2. The existence of the silenes has been postulated for 
many years on the basis of the products obtained from certain 
organosilicon reactions but it has only been recently that such materials 
were actually isolated so that their existence was proven. See Brook, A. 
G., Abdesaken, F., Gutekunst, B., Gutekunst, G., and Kallury, R. K., Chem. 
Comm., 191 (1981). The silenes can be generated from precursor silanes by 
several different methods, for example by pyrolytic decomposition: 
Guselnikow, L. E., Flowers, M. C., Chem. Comm., 64 (1967); thermal 
rearrangement: Slutsky, J., Kwart, H., J. Org. Chem., 38, 3659 (1973); 
photochemical rearrangement: Nahadaira, Y., Kanovchi, S., Sakurai, H., J. 
Am. Chem. Soc., 96 5621 (1974); elimination from silyl halides or esters: 
Jones, P. R., Lim, T. F. O., J. Am. Chem. Soc., 99, 2013 (1977); 
rearrangement of silyl carbenes: Barton, T. J., Holkman, S. K., J. Am. 
Chem. Soc. 102 1584 (1980); and, disproportionation of trimethylsilyl 
radicals: Tokach, S. K., Koob, R. D., J. Am. Chem. Soc., 102, 376 (1980 ). 
Such silenes include, for example, 
##STR4## 
These highly reactive silane intermediates react with the surface hydroxyls 
of porous materials upon contact with such hydroxyls. Thus, using 
(CH.sub.3).sub.2 Si.dbd.CH.sub.2 as an example of a silane, and using 
.tbd.SiOH as the designation for a surface hydroxyl on silica, the 
following reaction is believed to take place: 
EQU .tbd.SiOH+(CH.sub.3).sub.2 Si.dbd.CH.sub.2 
.fwdarw..tbd.SiOSi(CH.sub.3).sub.3. 
Another group of highly reactive silane intermediates useful in this 
invention are the silylenes. Their general structure is notable owing to 
the presence of a radical, i.e. &gt;Si:. Silylenes can be formed from 
disilanes, for example, methoxydisilanes which undergo thermally induced 
alpha-elimination to produce the organosilylenes. 
##STR5## 
See Atwell, W. H. and Weyenberg, D. R., J. Am. Chem. Soc., 90, 3438 
(1968). Such reactive silane intermediates can also be generated via 
photochemical methods as shown, for example, in Sakurai, H., Kobayashi, 
Y., and Nahadaira, K., J. Am. Chem. Soc., 93, 5272 (1971). 
Such silylenes include, for example, 
##STR6## 
These highly reactive silane intermediates react with the surface hydroxyl 
of porous materials upon contact with hydroxyls. Thus, using 
(CH.sub.3).sub.2 Si: as an example of a silylene, and .tbd.SiOH as the 
designation for a surface hydroxyl on silica, the following reaction is 
believed to take place: 
EQU .tbd.SiOH+(CH.sub.3).sub.2 Si:.fwdarw..tbd.SiO{Si(CH.sub.3).sub.2 }.sub.x H 
where x is an integer of less than about 10. 
Another group of highly reactive silane intermediates useful in this 
invention are the silanones. Their general structure is notable owing to 
the presence of a ketonic oxygen, i.e. &gt;Si.dbd.O in the molecule. Like the 
silenes, the silanones are suspected to exist but have never been isolated 
and identified. However, strong evidence exists that they are present in 
an operational sense in certain reaction mixtures. See, for example, H. 
Okinoshima and W. P. Weber, J. Organometal. Chem., 155, 165, (1978) and T. 
J. Barton and W. D. Wulff, J. Am. Chem. Soc., 101, 2735 (1979). 
These highly reactive silane intermediates react with the surface hydroxyls 
of porous materials upon contact with such hydroxyls. Thus, using 
(CH.sub.3).sub.2 Si.dbd.O as an example of a silanone, and .tbd.SiOH as 
the designation for a surface hydroxyl on silica, the following reaction 
is believed to take place: 
EQU .tbd.SiOH+(CH.sub.3).sub.2 Si.dbd.O.fwdarw..tbd.SiO{(CH.sub.3).sub.2 
SiO}.sub.y H 
where y is an integer of less than about 10. 
The porous materials found useful in this invention are those materials 
which are porous solids, having hydroxyl groups on their surfaces. Such 
materials for example are silicas, silica gels, stannia, alumina, titania, 
zirconia, and the like. Also, these materials can be porous glass, 
controlled pore glass, controlled pore ceramics or plastic as long as the 
material has, or will form, hydroxyl groups on its surface. 
The form of the porous material is not overly critical. Particulate porous 
materials, as well as filaments, slabs, discs, blocks, spheres, films and 
other such forms can be used in this invention. Also contemplated within 
the scope of this invention is the treatment of particulate materials by 
the process of this invention, and the subsequent forming of the treated 
particulate materials into filaments, slabs, discs, blocks, spheres, 
films, membranes, sheets, and the like. 
Preferred for this invention are the porous metalloid and metallic oxides 
such as silica, alumina, zirconia and titania in all of their related 
forms. Most preferred are the silicas. Also contemplated within the scope 
of this invention are porous mixed metallic oxides such as Na.sub.2 O: 
Al.sub.2 O.sub.3 :5SiO.sub.2 :nH.sub.2 O, wherein n is the moles of water 
of hydration, and the like. 
The first phase of this process is the contacting of the porous material 
with the reactive silane intermediate. As indicated above, the reactive 
silane intermediates are formed from silane precursors and one method is 
to have the porous material be intimately contacted with a solution of the 
precursor silane so that when the silane precursor generates the reactive 
silane intermediate, the reactive silane intermediate can immediately 
contact the exterior surface of the porous material and react with it. 
Failure to intimately contact the porous material with the silane 
precursor while the reactive silane intermediate is being formed, results 
in a wasteful use of the reactants, since the reactive silane intermediate 
tends to react with itself or with newly formed surface bonds, or reaction 
container walls. For this method it is preferred that adsorbed water be 
present in the pores to reduce entry of the silane precursor. This water 
also reduces the opportunity for the reactive silane intermediate to reach 
deep into the pores. 
Thus, in one method the silane precursor in a solvent solution such as 
benzene or toluene is intimately contacted with the porous material. If 
particulate, the porous material is used as a suspension. The reactive 
silane intermediate is then generated in-situ, for example, by the 
application of ultraviolet light to the solution, and the reactive silane 
intermediate makes immediate contact with the exterior surface of the 
porous material and decreases the chances of ineffective use of the 
reactive silane intermediate. 
In another method, the reactive silane intermediate can be generated in a 
chamber independent of the liquid dispersion of the porous material and 
transported by some means to the liquid dispersion of the porous material. 
For example, the precursor silane in solvent solution can be passed 
through an irradiation zone where the reactive intermediates are generated 
and the solvent solution flow carries the generated reactive silane 
intermediates to the porous material. Flow recycling of unexpended 
precursor silane allows effective utilization of the precursor silane to 
treat the exterior surface of the porous material. 
It is also contemplated within the scope of this invention to carry out the 
first phase of the process in a vapor phase. Thus, in a third method the 
precursor silane is placed in a chamber and contacted with the equilibrium 
vapor of the reactive silane intermediate. The chamber has two regions, 
one, an irradiation region and, two, a reaction region. The silane 
precursor is irradiated in the irradiation region to generate the reactive 
silane intermediate which moves toward the porous material in a random 
fashion. The porous material which is also located in the reaction region 
of the vacuum chamber, and some short distance away from the zone of 
irradiation, is thereby randomly hit on the exterior surface with the 
reactive silane intermediate thereby causing a reaction between the 
reactive silane intermediate and the exterior surface hydroxyls of the 
porous materials. In a fourth method, the precursor silane vapor chamber 
can be equipped to allow a flow of gas, such as helium, to remove the 
reactive silane intermediate as well as unreacted precursor silane vapor. 
This helium flow then carries the reactive silane intermediate to the 
porous material for reaction therewith. These methods and their variations 
allow for more selective exterior surface treatment, as the excitation 
used to generate the reactive silane intermediate is not allowed to 
contact the porous material and, thus, the precursor silane need not be 
kept out of the pores to prevent reaction with the interior hydroxyls. It 
is obvious then that the resulting porous material is not generally 
reacted on the interior surfaces in this phase of the process nor do the 
pores contain the dihydroxy monomers or oligomers. Thus, when the reactive 
silane of the second phase, i.e. step (III) of this inventive process, is 
contacted by the surface treated porous material of steps (I) and (II), 
only the moiety resulting from the reactive silane will be found on the 
interior surface of the pores, resulting in a "purer" dual surface 
material. Steps (I) and (II) can be carried out for a period of time of 
from 1 minute to 24 hours. Generally, for purposes of this invention it is 
preferred to carry out steps (I) or (II) over about a 1 to 8 hour time 
period to ensure that the exterior surface of the porous material is well 
treated. 
The temperature at which steps (I) and (II) are carried out is not narrowly 
critical and can range from 0.degree. C. to 400.degree. C. Preferred is a 
room temperature to 200.degree. C. reaction temperature. 
The amount of reactve silane intermediate useful in this invention depends 
on the number of exterior surface hydroxyls to be reacted. Typically, a 
stoichiometric amount equivalent to the exterior surface hydroxyls plus 
some excess of the reactive silane intermediate is required to cover all 
surface hydroxyl because of the potential side reactions involved. 
Typically, 50 to 1000% excess is used. This excess is with respect to the 
exterior hydroxyl groups. With respect to the total hydroxyls on both the 
exterior and interior surfaces, the amount of the reactive silane 
intermediate amounts to about 0.001 to 1%. When adsorbed water is present 
in the pores to consume excess amounts of the reactive silane 
intermediate, much larger amounts of the intermediate are tolerable, up to 
100% of the total hydroxyls present. If it is desirable to achieve less 
than stoichiometric coverage of the surface hydroxyls, then obviously, 
less reactive silane intermediate should be used. 
In the second phase of the process, i.e. step (III), the material obtained 
by steps (I) and (II) is contacted with a reactive silane. It should be 
noted that steps (I) and (II) deal with a "reactive silane intermediate" 
while step (III) deals with a "reactive silane". For purposes of this 
invention, what is meant by "reactive silane" is that the silane is 
sluggish in its reactivity such that it will not react with nor displace 
the newly formed groups on the exterior surface of the porous material but 
will react with the silica silanols. This reaction is preferably carried 
out in bulk solution as the reactive silanes are generally neither 
reactive enough or volatile enough to use as vapors. Thus, the reactants 
are mixed together in a solvent solution, with or without, heating. The 
object of step (III) is to allow the hydrolysis and diffusion, or the 
diffusion and hydrolysis of the reactive silane, in the pores of the 
porous material. Since the exterior surface hydroxyls of the porous 
material have been effectively covered by the reactive silane intermediate 
in steps (I) and (II), the reactive silane does not have available to it 
the reactive sites on the exterior surface of the porous material. Thus, 
the reactive silane has only the hydroxyls remaining on the interior 
surfaces of the porous material available for reaction. 
Therefore, step (III) must be carried out for a sufficient period of time 
to allow for the diffusion of the reactive silane into the pores, and 
hydrolysis of the silanes therein (or hydrolysis of the silane and then 
diffusion of the hydrolyzate into the pore to react). Some of the more 
highly reactive silanes which do not require hydrolysis prior to reaction 
with the interior hydroxyl groups may also be used as vapors. 
Step (III) can be carried out for a period of time of from several minutes 
to several hours. As indicated above, this phase of the process depends on 
the rate of hydrolysis of the reactive silane and the rate of diffusion of 
the silane, or its hydrolysis product, into the pores of the porous 
material. Preferred for this invention is a reaction time for step (III) 
of from 10 minutes to 24 hours. Most preferred is a time of 1 to 6 hours. 
The temperature at which step (III) is carried out is more critical than 
steps (I) and (II), yet it is not narrowly critical. As one would expect, 
increased temperatures enhance the rate of reaction but, increasing the 
temperature does not appear to promote undesirable side reactions. Thus, 
the temperature used in step (III) can range from 0.degree. C. to 
300.degree. C. Most preferred is the reflux temperature of the reaction 
mixture at about 70.degree. C. to 120.degree. C. 
The amount of reactive silane useful in this invention depends on how many 
of the surface hydroxyls of the pore interior one wishes to cover. An 
excess of the reactive silane is not critical as this reactive silane does 
not displace any of the exterior surface groups obtained by steps (I) and 
(II). Typically, a stoichiometric quantity, based on reactive hydroxyls of 
the interior pore surfaces, is used herein. 
If the reactive silane is very sluggish (e.g., organosilanol), then the 
reaction should be catalyzed with acid or base. In the case of the treated 
porous material having the groups on the exterior surface derived fron 
silanones, the reaction cannot be catalyzed with acid and must be 
catalyzed with base, preferably weak base. In the case of the treated 
porous material having the groups on the exterior surface derived from 
silenes and silylenes, both acid and base catalysis can be used, with the 
proviso that the minimum catalysis required for completion of the reaction 
be used. The time and temperature of such catalyzed silylations must be 
carefully adjusted by trial and error to attain adequate interior coverage 
before the displacement of the covalently bound external group begins. 
It will be recalled from the foregoing discussion that dihydroxy compounds 
and oligomers can reside in the interiors of the pores. This is true as 
long as there is an absence of catalysts. It is known by the inventors 
herein that the introduction of the reactive silane in this third step, 
tends to displace these dihydroxy compounds and oligomers from the pore 
interior and that such displacement did not occur on the exterior surface 
of the porous material. The process therefore appears to give dual surface 
compositions. 
The reactive silanes useful in step (III) of this invention are those 
silanes which are recognized as conventional silylation reagents. This 
group includes such silanes as alkoxysilanes, chlorosilanes, 
acetoxysilanes, alkyldisiloxanes, silylamines, silylamides, 
silylthioethers and many others. Preferred for this invention are 
alkoxysilanes, silylamides, and silylamines. 
Specific silanes which are useful herein include: trimethylchlorosilane; 
dimethyldichlorosilane; hexamethyldisilazane; 
N,N'-bis(trimethylsilyl)urea; N-trimethylsilyldiethylamine; 
N-trimethylsilylimidazole; N,O-bis(trimethylsilyl)acetamide; 
N,O-bis(trimethylsilyl)trifluoroacetamide; 
N-methyl-N-trimethylsilyltrifluoroacetamide; 
t-butyldimethylsilylimidazole; N-trimethylsilylacetamide; 
N-trimethylsilylpiperidine; hexamethyldisilthiane; 
O-trimethylsilylacetate; O-trimethylsilyltrifluoroacetate; 
N-trimethylsilyldimethylamine; N-trimethylsilylmorpholine; 
N-trimethylsilylpyrrolidine; and N-trimethylsilylacetanilide. In addition, 
silanes having desirable functional groups may also be used. For example, 
such silanes as N-(vinyldimethylsilyl)N-methylacetamide is an excellent 
silane to use in this invention because it leaves the vinyldimethylsilyl 
group on the interior surface of the porous material. The vinyl group is 
valuable because once the vinyl group is attached to the interior surface 
of the porous material, conventional reactions can be used to add to the 
vinyl group thus creating yet another type of group on the interior 
surface of the porous material. For example, when the porous material is 
treated with N-(vinyldimethylsilyl)N-methylacetamide, one can add 
HSCH.sub.2 COOH to the resulting vinyl dimethyl silyl to give a surface 
group such as HOOCCH.sub.2 S(CH.sub.2).sub.2 (CH.sub.3).sub.2 SiOSi.tbd.. 
Using bis(dimethylsilyl)N-methylacetamide gives a surface treatment such 
as H(CH.sub.3).sub.2 SiOSi.tbd. which can also be further reacted with 
unsaturated molecules to provide further modifications to the interior 
surface of the porous material. 
Yet another aspect of this invention is the use in step (III) of 
organosilanes to silylate the porous material. Such silanes useful in this 
invention include, for example, 
(alpha-methacryloxypropyl)trimethoxysilane; (4-aminopropyl)triethoxysilane 
; {gamma-(beta-aminoethylamino)-propyl}trimethoxysilane; 
(gamma-glycidoxypropyl)trimethoxysilane; 
{beta-(3,4-epoxycyclohexyl)-ethyl}trimethoxysilane; 
(beta-mercaptoethyl)trimethoxysilane; 
(gamma-mercaptopropyl)trimethoxysilane; 
(gamma-chloropropyl)trimethoxysilane; 
##STR7## 
When it is determined that the reaction in step (III) is essentially 
finished, the product is typically isolated from the reaction mixture. 
Thus, step (IV) of this process is the isolation of such products from the 
reaction mixture. This can be accomplished in a number of ways. For 
example, the liquid can be decanted, the porous material washed and the 
liquid decanted successively or, the reaction mixture can be filtered to 
remove the liquid from the solid product. The final product can be used in 
this form or it can be dried. If the material is in a particulate form it 
can be used as is or it can be compressed, sintered, or otherwise formed. 
It is also contemplated within the scope of this invention to prepare a 
dual-surface porous material by eliminating step (III) of the defined 
process. The elimination of step (III) of the process results in an 
"intermediate" product wherein the surface of the porous material is first 
treated by steps (I) and (II) to provide a treated porous material having 
(CH.sub.3).sub.3 SiO, H{(CH.sub.3).sub.2 Si}.sub.x O or 
H{OSi(CH.sub.2).sub.2 }.sub.y O on the exterior surface and hydroxyl 
groups on the interior pore surface. 
Thus, this invention also consists of a method of preparing a dual surface, 
porous material which comprises: 
(A) contacting a porous material with a highly reactive silane intermediate 
capable of forming covalent bonds with hydroxyl groups on the exterior 
surface of the porous material; 
(B) allowing the mixture from (A) to react thereby treating the porous 
material exterior surface; 
(C) subsequently isolating the dual surface porous material from the 
mixture of (B). 
These intermediates are useful products for the method disclosed supra for 
providing dual surface materials using reactive silanes to treat the 
interior pore surfaces. 
It is a further object of this invention to provide a composition of matter 
consisting of a porous material having reacted to its exterior surface, 
silanol-containing groups which are not silica-silanols and whose interior 
pore surface contains silica-silanol or other hydroxyl groups different 
from the exterior groups. 
The dual-surface porous materials of this invention are useful for 
chelating metals from solution and high performance liquid chromatography 
methods (see Instrumental Methods of Analysis, Sixth edition, Willard, H. 
H., Merritt, Lynne L. Jr., Dean, John A. and Settle, F. A., Jr. D. Van 
Nostrand Co., N.Y. 1981, pages 529-564). The materials, whose surfaces 
bear groups capable of further modification, such as H(CH.sub.3).sub.2 
SiO-- and CH.sub.2 .dbd.CH(CH.sub.3).sub.2 SiO--, are useful intermediates 
in the preparation of other surface-modified porous materials. Such 
modifiable groups are particularly valuable when on the exterior surface. 
Now, so that those skilled in the art may appreciate and understand the 
invention described herein, the following examples are offered for 
illustration purposes only. The examples should not be construed as 
limiting the invention as defined in the claims.

EXAMPLE 1 
A porous particulate SiO.sub.2 with a mesh size of 60-200 on U.S. standard 
sieves, having a surface area of approximately 300 m.sup.2 /g and an 
average of 60 angstrom units pore size, purchased from J. T. Baker Co., 
Phillipsburg, N.J., as Cat. No. 3405-1 was dried for 2 hours at 
110.degree. C. in an air convection oven to remove excess water, but not 
completely remove adsorbed water from the material. Into a two-necked, 50 
ml. round bottomed glass flask, there was placed 1.0181 gms. of the dried 
SiO.sub.2, 0.5541 gms. of dodecamethylcyclohexasilane and 14 mols of dry 
benzene, all under an argon blanket. This solution was stirred and 
irradiated at room temperature using a Rayonet.RTM. ultraviolet light 
source at 2537 angstrom units (Rayonet photochemical reactor manufactured 
by Southern New England Ultraviolet Company, Hamden, Conn., U.S.A). After 
about 5 hours, a gas-liquid chromatograph analysis showed that about 50% 
of the cyclic silane had been consumed. At this point, apparently no 
higher molecular weight oligomers had formed as evidenced by the lack of 
elution of the same on the chromatograph. After about 20 hours of total 
irradiation, the cyclic silane had been totally used up. The product 
mixture was filtered and washed with dry reagent toluene. A yellow-colored 
polymeric substance coated on the surface of the silica was removed by 
washing with dry heptane followed by a wash with pure ethanol. The solid 
product was then dried in an air-circulating oven for 2 hours at 
60.degree. C. 
An untreated sample of the SiO.sub.2 used in this example was analyzed for 
carbon content and it was found to contain 0.12 weight percent carbon 
while the treated SiO.sub.2 of this example showed 4.76 weight percent 
carbon. Bulk analysis thus indicates that there is present 1.98 m mole of 
H(CH.sub.3).sub.2 Si/gm of SiO.sub.2. The larger portion of 
H(CH.sub.3).sub.2 Si was subsequently displaced as discussed infra. The 
precursor silane is excluded from the pore regions of the particles by 
virtue of such region's high polarity and preferential adsorption of water 
rather than non-polar compounds such as, for example, toluene. 
EXAMPLE 2 
The treated product from example 1 was subjected to a second treatment 
using (CH.sub.3 O).sub.3 Si(CH.sub.2).sub.3 NH(CH.sub.2).sub.2 NH.sub.2 by 
mixing 0.1 gms. of the treated material from example 1 with a 5 weight 
percent dry toluene solution of the silane (0.08 ml in 1.42 ml dry 
toluene). After about one and one-half hours of refluxing under nitrogen, 
the reaction was cooled and the gel separated by filtration and washed 
with reagent grade toluene and dried in an air-circulating oven at 
60.degree. C. for two hours. 
This material when analyzed by a comparison of bulk elemental analysis (%C 
and %N) with surface elemental analysis by ESCA (Electron Spectroscopy for 
Chemical Analysis) showed the following for the treated SiO.sub.2 : 
The ratio of O.sub.3/2 Si(CH.sub.2).sub.3 NH(CH.sub.2).sub.2 NH.sub.2 
groups to 
##STR8## 
groups equalled 0.88 for the interior surface and 0.29 for the exterior 
surface. Thus, this comparison shows that the interior surface of the 
silica has predominantly more O.sub.3/2 Si(CH.sub.2).sub.3 
NH(CH.sub.2).sub.2 NH.sub.2 moieties than (CH.sub.3).sub.2 HSi-- moieties, 
while the reverse is true on the exterior surface. Hence, a dual-natured 
porous material had been achieved. 
Conditions were not optimized for obtaining complete exclusion of the 
interior silane moiety, O.sub.3/2 Si(CH.sub.2).sub.3 NH(CH.sub.2).sub.2 
NH.sub.2, from the exterior surface, but as the analysis indicates, the 
(CH.sub.3).sub.2 HSi-- moiety predominates. The bulk elemental analysis 
(%C and %N) before and after the reactive silane treatment shows that 
silylation of the particles was accompanied by displacement of about half 
of the (CH.sub.3).sub.2 HSi-- moiety from the interior pore regions. Such 
major displacement did not occur on the exterior surface. This suggests, 
but the inventors are deemed not to be held to such a theory, that easily 
displaced, hydrogen-bonded (CH.sub.3).sub.2 Si(OH).sub.2 and its oligomers 
were formed and are present in the pores. Such species form easily by the 
reaction of (CH.sub.3).sub.2 Si.dbd. with pore water and are not 
themselves very reactive with silica silanols in the absence of catalysts. 
Thus, this theory explains in part why the surface of the particulate 
material is preferentially treated over the interior surface, when 
contacted with the reactive silahe intermediate. 
EXAMPLE 3 
The treated material from example 2 was shown to be able to chelate copper 
ions from a copper sulfate solution. Upon contacting the copper solution, 
the white powder changed to a deep blue color characteristic of copper 
fully bound to the entire porous surface of silica whereas ESCA detected 
only minor amounts of exterior surface copper.