Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
2003-02-03
2004-07-13
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...
Reexamination Certificate
active
06762270
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polyurethane prepolymers having terminal alkoxysilane and OH groups and prepared from high molecular weight polyurethane prepolymers with reduced functionality, a method of preparing them by premature termination of the synthesizing reaction and their use as binders for low-modulus sealants and adhesives.
BACKGROUND OF THE INVENTION
Alkoxysilane-functional polyurethanes which are cross-linked by silane polycondensation have been known for a long time. A summarizing article on this subject is contained e.g. in “Adhesives Age” April 1995, pp. 30 ff. (authors: Ta-Min Feng, B A Waldmann). Alkoxysilane-terminated, moisture-curing, one-component polyurethanes of this type are increasingly used as flexible coatings, sealants and adhesives in building and the automobile industry. In these applications the most important properties are elongation, adhesion and curing speed. However these properties required particularly in building cannot be fully achieved by these systems.
EP-A-596 360 describes alkoxysilyl-functional polyurethane prepolymers which are suitable for use as sealant binders. Due to the use of relatively short-chain polyethers made by KOH catalysis and having a high content of terminal double C═C bonds the products explicitly described in this application do not achieve the high molecular weight which is necessary for the preparation of soft and low-modulus sealants, such as those used in the construction industry.
An alkoxysilyl-functional polyurethane prepolymer which may be employed as a building sealant is described in WO 00/26271. A high molecular weight polypropylene oxide polyether prepared by two-metal cyanide catalysis is used, and guarantees relatively low viscosity in prepolymer synthesis when combined with secondary aminosilanes. Such compounds have a number average molecular weight (calculated from NCO and functionality) of over 15 000 g/mol and a range of properties that are suitable for use as building sealants. However, the viscosities of these systems are considerably high, which considerably restricts their range of applications.
DE-A 3629237 describes an alkoxysilyl-functional polyurethane system which achieves a better elongation by reducing functionality. This is done by subsequently lowering functionality either with monoalcohols or by employing monoisocyanates. However the properties required for a building sealant are not obtained in this way.
Polyurethane prepolymers with terminal alkoxysilyl groups and a long shelf life are known from WO 92/05212. Despite their relatively low number average molecular weights, they have relatively high viscosity. Also, an additional step in the reaction, using monoalcohols, is required to reduce their functionality. The use of high molecular weight polyethers in the preparation of sealant prepolymers is described in WO 99/48942. A reactive thinner project is disclosed, which also includes the use of low-functional constituents. The properties of the resulting cured polymer are said to be largely unaffected. However, this makes it necessary to synthesise a second polyurethane.
Prepolymers containing terminal alkoxysilane and OH groups are also known. A pressure-sensitive adhesive based on these compounds is described in DE-A 3 220 865. The specification describes the synthesis with adducts of diisocyanate and aminosilanes, though this has the drawback of two-stage synthesis. In addition, the diadduct of two molecules of aminosilane and diisocyanate will form and expensive aminosilane will thus be lost, leading to greater hardness which is undesirable in the sealants field.
An object of the present invention is to prepare polyurethane prepolymers having terminal alkoxysilane groups which overcome the described disadvantages of the prior art.
This object may be achieved with the high molecular weight polyurethane prepolymers having terminal alkoxysilane and OH groups of the present invention, which are described in detail below.
SUMMARY OF THE INVENTION
The present invention relates to polyurethane prepolymer having terminal alkoxysilane and OH groups which is the reaction product of
A) a polyurethane prepolymer prepared by incomplete reaction, of
i) an aromatic, aliphatic or cycloaliphatic diisocyanate component having an NCO content of 20 to 60% by weight with
ii) a polyol component comprising a polyoxyalkylene diol having a number average molecular weight of 3000 to 20,000,
wherein the reaction is stopped after 50 to 90% of the OH groups of component ii) are reacted and 10 to 50% are unreacted, with
B) a compound having alkoxysilane and amino groups, of formula (I)
wherein
X, Y and Z are the same or different and represent linear or branched C
1
-C
8
alkyl or C
1
-C
8
alkoxy radicals, provided that at least one of the radicals represents a C
1
-C
8
alkoxy group,
R represents a linear or branched alkylene radical with 1 to 8 carbon atoms,
R′ represents hydrogen, a C
1
-C
8
alkyl radical, a C
6
-C
10
aryl radical or a radical of formula (II)
wherein
R″ and R′″ are the same or different and represent linear or branched alkyl radicals with 1 to 8 carbon atoms.
The present invention also relates to a process for preparing these polyurethane prepolymers containing terminal alkoxysilane and OH groups and to isocyanate-free, sealants, adhesives, primers and coatings containing these polyurethane prepolymers containing terminal alkoxysilane and OH groups as binders.
DETAILED DESCRIPTION OF THE INVENTION
In formula (I) X, Y and Z preferably represent methoxy and/or ethoxy groups and R′ preferably represents a radical of formula (II).
The lowering of the functionality of the prepolymers according to the invention leads to a low-modulus polymer. Prepolymers with a relatively low mean molecular weight and low viscosity can thereby be used to achieve excellent properties. The prepolymer according to the invention obtains this range of properties through incomplete conversion of the OH groups of the polyethers used with a diisocyanate and subsequent termination of the terminal NCO groups with aminosilanes. The remaining OH groups have been found, surprisingly, not to shorten the shelf life and not to be involved in the polymerisation process even during curing.
Polyurethane prepolymer A) is prepared by reacting an excess of diisocyanate component i) with polyol component ii) such that 50 to 90% of the OH groups of polyol component ii) are reacted with the NCO groups of diisocyanate component i) and 10 to 50% of the OH groups of polyol component ii) are not reacted in polyurethane prepolymer A). The resulting prepolymer A) contains both isocyanate groups and OH groups.
Isocyanates which may be used as polyisocyanate component i) include aliphatic, cycloaliphatic or aromatic diisocyanates having an isocyanate content of 20 to 60% by weight. The term “aromatic” or “cycloaliphatic” diisocyanates refers to those with at least one aromatic or cycloaliphatic ring per molecule in which at least one of the two isocyanate groups is preferably, but not necessarily, directly linked to an aromatic or cycloaliphatic ring. Examples of aromatic and cycloaliphatic diisocyanates are those having a molecular weight of 174 to 300, such as 4,4′-diphenylmethane diisocyanate or mixtures thereof with 2,4′-diphenylmethane diisocyanate, 2,4-diisocyanatotoluene and mixtures thereof with preferably up to 35% by weight, based on the weight of the mixture with 2,6-diisocyanatotoluene, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), bis-(4-isocyanatocyclohexyl)-methane, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl-cyclohexane and 1,3-diisocyanato-6-methyl-cyclohexane, optionally in admixture with 1,3-diisocyanato-2-methylcycloyhexane. Mixtures of these isocyanates may also be used.
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI) is particularly preferred as component i).
Polyol component ii) contains as its major component (>50 by weight) a polyoxyalkylene diol having a number average molecular weight of 3000 to
Groth Stefan
Ludewig Michael
Matner Mathias
Ruttmann Gerhard
Bayer Aktiengesellschaft
Gil Joseph C.
Matz Gary F.
Moore Margaret G.
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