Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2001-02-07
2003-02-04
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S026000, C528S025000, C556S413000, C556S414000
Reexamination Certificate
active
06515096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to stable 1:1 monoadducts of secondary aminoalkylalkoxysilanes and diisocyanates having a free diisocyanate content of less than 0.6% by weight and to a process for preparing the adducts. These monoadducts comprise difunctional monomers containing urea groups, a reactive isocyanate function, and crosslinkable silicon.
2. Discussion of the Background
The monoadducts of aminoalkylalkoxysilanes and diisocyanates belong to the class of the isocyanatoorganosilanes. A series of processes has been developed for preparing isocyanatoorganosilanes, these processes differing in terms, for example, their economics, efficiency, yield, and technical prerequisites (cf. EP 0 649 850). The process of the invention described herein is suitable both for preparing laboratory amounts and for industrial scale production.
Owing to their difunctionality, isocyanatoorganosilanes are synthesis building blocks of diverse usefulness which combine the high surface activity of the siloxanes with the high reactivity of the isocyanates and can be utilized to combine conventional polymer chemistry with silicone chemistry. The hydrolyzable silyl group is able to crosslink by way of a “silane polycondensation” in the presence of moisture, and the isocyanate groups as well are able to combine with one another under the effect of moisture. In addition to the reaction with hydroxy-functional coreactants, the isocyanate group offers the further option of the NCO/NH reaction. Both functionalities make it possible in principle to effect chemical attachment of the building block to customary polymer materials and thus a tailored modification of these materials
The literature describes moisture-curing sealing compounds based on totally or partially silane-capped, isocyanate-terminated polyurethane prepolymers (EP 0 355 426, EP 0 082 528, DE 27 38 979, DE 34 26 987, EP 0 158 893, U.S. Pat. No. 4,374,237). Monoadducts of aminoalkylalkoxysilanes and diisocyanates have been used to prepare such systems. They also find application in the field of crosslinkable adhesives (DE 32 20865, DE 32 22 860). EP 0 182 924 describes the preparation and use of adhesion-promoting coatings of poly(meth)acrylates and isocyanate-functional alkoxysilanes, and EP 0 268 559 describes silicon-modified isophorone isocyanates as adhesion promoters. In principle, silicon-modified isocyanates containing urea groups are also suitable for such an application.
1:1 adducts of diisocyanates and aminoalkylalkoxy-silanes are not unknown (cf., e.g., DE 32 20 865). Their mode of preparation - reacting the two components in a molar ratio of approximately 1:1 - has the inevitable consequence, however, that they are obtained not in pure, isolated form but rather as a mixture containing relatively large amounts of bisadduct (diisocyanate-aminoalkylsilane 1:2) and unreacted diisocyanate. Unlike the 1:1 adduct, the former, as a disilane compound, is no longer a difunctional building block having chemical functions which are reactive independently of one another. It impairs the quality of the monoadduct and may also not be without deleterious effects on the quality and pattern of properties of the target end products. A high proportion of monomeric diisocyanate is intolerable from a toxicological standpoint. Isocyanates are highly reactive compounds, and many representatives of this class are classified as toxic. A high residual proportion of monomeric diisocyanate in the product must absolutely be avoided, since isocyanates are taken in predominantly by way of the respiratory tract and the vapor pressure of the monomer is much higher than in the case of the 1:1 adduct.
It is known that primary aminoalkylsilanes are unsuitable for the partial end capping of NCO prepolymers because the free isocyanate groups react further with the urea groups of the capped termini to form biurets. Gelling is the consequence in this reaction. According to U.S. Pat. No. 4,374,237, in contrast to the teaching of U.S. Pat. No. 3,627,722 and U.S. Pat. No. 4,067,844, the gelling problem cannot be solved even by using customary secondary aminoalkylsilanes instead of primary aminoalkylsilanes. A surprising exception specified is a group of particular secondary aminoalkylsilanes, including N,N-bis[(3-triethoxysilyl)propyl]amine as a suitable representative example.
Furthermore, experiments have shown not only that NCO-containing adducts of isocyanates and aminoalkylalkoxysilanes are hampered by the problem of gelling as a result of biuret formation but also that there is a marked instability with respect to cleavage back to the starting materials. This tendency for reversal of the formation reaction—the urea group breaks down with reformation of the isocyanate group and the amine—has been observed for primary and secondary aminoalkylsilanes, including N, N-bis[(3-triethoxysilyl)propyl]amine.
It would be advantageous and desirable if the target monoadducts (1:1) of aminoalkylalkoxysilanes and diisocyanates did not have the disadvantages described above.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide gelling-stable and recleave-stable monoadducts (1:1) of aminoalkylalkoxysilanes and diisocyanates having a relatively low free diisocyanate content.
Surprisingly, the present invention demonstrates that it is possible to obtain low-monomer, stable monoadducts (1:1) of aminoalkylalkoxy-silanes and diisocyanates by reacting particular secondary aminoalkylalkoxysilanes with diisocyanates and subsequently conducting a monomer separation by short path distillation.
The invention provides stable 1:1 monoadducts of aminoalkylalkoxysilanes and diisocyanates having a free diisocyanate content of less than 0.6% by weight, where the adducts comprise secondary aminoalkylalkoxysilanes of the formula I:
where
R
1
and R
2
are identical or different C
1
-C
8
alkyl groups;
R
3
is a C
1
-C
5
alkylene group;
R
4
and R
5
are identical or different C
1
-C
18
alkyl groups or alkoxyalkylene groups having up to 5 carbon atoms; and
n is 0, 1 or 2; and diisocyanates.
Accordingly, the present invention provides a stable 1:1 monoadduct of
(a) at least one aminoalkylalkoxysilane represented by formula I:
wherein
R
1
and R
2
are identical or different C
1
-C
8
alkyl groups;
R
3
is a C
1
-C
5
alkylene group;
R
4
and R
5
are identical or different C
1
-C
8
alkyl groups or alkoxyalkylene groups having up to 5 carbon atoms; and
n is 0, 1 or 2; and
(b) at least one diisocyanate,
wherein the monoadduct has a free diisocyanate content of less than 0.6% by weight.
The present invention also provides a process for preparing the stable 1:1 monoadduct, comprising:
reacting said aminoalkylalkoxysilane and said diisocyanate to produce said monoadduct, to produce said monoadduct, and then
removing unreacted diisocyanate such that the diisocyanate content of said monoadduct is less than 0.6% by weight.
The present invention additionally provides a process for preparing stable 1 :1 monoadducts of aminoalkyl-alkoxysilanes and diisocyanates having a free diisocyanate content of less than 0.6% by weight, which comprises reacting 5-20 mol of diisocyanate with 1 mol of aminoalkylalkoxysilane, the diisocyanate being introduced initially at room temperature and the aminoalkylalkoxysilane being added dropwise to this initial charge at a rate such that the temperature increase does not exceed 100° C., and, after the end of the reaction, separating off the unreacted diisocyanate from the reaction product by means of a flash distillation at 80-160° C./0.04-0.2 mbar.
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Secondary aminoalkylalkoxysilanes of the invention are those represented by formula
where
R
1
and R
2
are identical or different C
1
-C
8
alkyl groups, preferably C
1
-C
4
alkyl groups;
R
3
Kohlstruk Stephan
Windmueller Manuela
Degussa - AG
Oblon, spivak, McClelland, Maier & Neustadt, P.C.
Peng Kuo-Liang
LandOfFree
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