Organic/inorganic composites with low hydroxyl group...

Details Organic/inorganic composites with low hydroxyl group... Organic/inorganic composites with low hydroxyl group...

1999-08-19

2001-10-16

Moore, Margaret G. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S042000, C528S039000, C524S789000, C524S780000, C524S783000, C524S784000, C524S786000, C524S788000, C523S213000

Reexamination Certificate

active

06303730

ABSTRACT:

The present invention relates to preferably transparent organic/inorganic composites with low hydroxyl group content, methods for their production and their application.
The present invention was based on the problem of developing preferably transparent composite materials based on silica heteropolycondensates which materials show an as low as possible takeup of water.
It is known that if such silica heteropolycondensates are prepared by the conventionally employed sol-gel process, they show a non-negligible content of OH groups which is due to the hydrolysis and condensation of the employed starting materials (silanes, etc.). Various ways of reducing said hydroxyl group content in such polycondensates have been proposed in the literature, e.g., by reacting said polycondensates with compounds which are reactive with water and OH groups. Typical examples thereof are the reaction with halides of the fourth main and sub groups of the Periodic Table (SiCl
4
, TiCl
4
, etc.) or with chlorine (e.g., in attempts to produce waveguide fibers based on SiO
2
having a low content of OH groups). In the cases described it is, however, usually not possible to lower the content of OH groups down to the ppb range.
Another proposed way is to keep the prepared silica heteropolycondensates from containing major amounts of water and SiOH groups from the beginning. This applies, e.g., to the reaction of alkoxysilanes with an excess of acid (see, e.g., Noll, W.: Chemie und Technologie der Silicone, Verlag Chemie, Weinheim, Bergstra&bgr;e, 1960, and Voronkov, M. G., Mileshkevich, V. P., Yuzhelevski, Yu. A., The Siloxane Bond, Plenum, New York, London, 1978, p. 236). In these reactions reactive intermediate compounds in the sense of alkylsilanes may in part be formed, which intermediate compounds in turn release water by ester cleavage (carboxylic acid esters or esters of mineral acids) during a condensation process, said water being, however, dispersed on a molecular level. Said water dispersed on a molecular level is then reused for hydrolysis and further condensation and is consumed thereby. The gross reaction can be represented by the following equation:
2≡Si—OR+HHal→≡Si—O—Si≡+ROH+RHal
 (Hal=halogen)
However, said reactions have usually not been employed for the preparation of extremely anhydrous condensates, but mostly for the homogeneous generation of the water required for the hydrolysis and condensation process (see, e.g., Schmidt, H.-K., Chemistry and Applications of Inorganic-Organic Polymers, Mat. Res. Soc. Symp. Proc., Vol. 73, 1986, p. 741). There, the “anhydrous” reaction path is taken in order to avoid the precipitation of oxides or hydroxides of reactive alkoxides (e.g., titanium alkoxide, aluminum alkoxide) in the presence of slowly reacting esters of silicic acid by direct addition of water. Concentrations of OH groups down to the ppm range are, however, not achievable in this manner.
As low as possible concentrations of OH groups of silica heteropolycondensates are desirable particularly because in combination with inorganic moieties, such as —Si—O—Si or —Si—O—Metal as present in such polycondensates, such OH groups result in a takeup of water which is dependent on the humidity of the air so that the desired goal of ensuring an extremely low water takeup cannot be achieved.
It has now surprisingly been found that the above problem can be solved by the combination of, i.a., the “anhydrous” reaction paths mentioned above and the increase in hydrophobicity of the network by the synthesis of inorganic/organic composite materials with a silica heteropolycondensate as network. Here, a silica network is first synthesized via the reaction principle described above. This may, e.g., be represented by the following general equations:
 ≡SiOR+HX&rlarr2;≡SiX+HOR
≡SiOR+≡SiX→≡Si—O—Si≡+XR
X=Hal, O—C(═O)—R, —NR
2
, etc.
R=Alkyl, Aryl, etc.
At least a part of the silanes employed for the above network synthesis has groups capable of forming organic polymer chains, e.g., (meth)acrylic or vinylic groups.
In order to increase the hydrophobicity of the network, additional silanes having hydrophobizing groups may be employed, e.g., those having (per)fluorinated side chains (particularly (per)fluorinated alkyl and aryl groups).
A further optional component are (per)fluorinated polymerizable organic monomers which can undergo a polymerization reaction with the polymerizable side chains of the above silanes. This is appropriate especially in cases where no silanes having (per)fluorinated side chains and groups, respectively have been employed for the synthesis of the silica network, as a certain content of fluorine of the composites according to the present invention is highly desirable.
As further optional component for the preparation of the composites with low hydroxyl group content according to the present invention nanoparticles having a low OH group content may also be employed, which particles are also available in accordance with the present invention.
Specifically, the present invention provides a process for the preparation of organic/inorganic composites lean in hydroxyl groups, which process comprises
(1) the non-hydrolytic condensation of one or more silanes, at least a part whereof has a group featuring at least one polymerizable carbon—carbon double or triple bond, which group is bonded to Si via an Si—C bond, the remaining groups on the Si atoms of the silanes which are not capable of undergoing condensation being preferably selected from saturated aliphatic and aromatic hydrocarbon groups which may optionally be substituted (preferably with halogen atoms such as F and Cl); and
(2) the thermal and/or photochemical polymerization of the condensation products of step (1).
Preferred embodiments of said process will be explained below.
According to a preferred embodiment the above process comprises
(a) the non-hydrolytic condensation of at least one chlorosilane of the general formula (1)
R
1
a
R
2
b
Si(Cl)
c
  (1)
wherein
R
1
is a group having at least one polymerizable carbon—carbon double or triple bond (preferably double bond) and is linked to Si via an Si—C bond, R
2
is an optionally substituted, saturated aliphatic or aromatic hydrocarbon group,
a=1 or 2,
b=0 or 1,
c=2 or 3,
wherein (a+b+c)=4;
optionally in combination with
(i) at least one chlorosilane of the general formula (2)
R
1
d
R
2
e
Si(Cl)
f
  (2)
 wherein
R
1
and R
2
are as defined above,
d=0 or 3,
e=0, 1, 2 or 3,
f=1, 2 or 3,
wherein (d+e+f)=4 and for d=3 or e=2 or 3 the groups R
1
and R
2
, respectively may be the same or different; and/or
(ii) at least one compound selected from the group consisting of tetrachlorides and tetrabromides of Ge, Si, Ti and Zr and AICl
3
and AlBr
3
;
by means of a condensing agent which is capable of non-hydrolytically condensing the above halogen compounds; or
(a′) the condensation of at least one alkoxysilane of the general formula (3)
R
1
a
R
2
b
Si(OR)
c
  (3)
wherein
R
1
, R
2
, a, b and c are as defined above and R represents alkyl (preferably having 1 to 4 carbon atoms such as methyl, ethyl, n- and i-propyl, preferably methyl or ethyl); optionally in combination with
(i′) at least one alkoxysilane of the general formula (4)
R
1
d
R
2
e
Si(OR)
f
  (4)
wherein
R
1
, R
2
, R, d, e and f are as defined above; and/or
(ii′) at least one compound of the general formula (5)
M(OR)
g
  (5)
wherein
R is as defined above,
M=Ge, Si, Ti, Zr or Al,
g=3 for M=Al and g=4 in all other cases;
by means of an anhydrous acid (e.g., a mineral acid such as HCl, HBr and Hl or an organic acid such as formic acid, acetic acid, trifluoroacetic acid, etc.);
(b) the thermal and/or photochemical polymerization of the condensation product of step (a) or (a′).
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