Metal-free silane-terminated polyurethanes, a process for...

Details Metal-free silane-terminated polyurethanes, a process for... Metal-free silane-terminated polyurethanes, a process for...

2002-03-29

2004-08-31

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...

C528S038000

Reexamination Certificate

active

06784272

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silane-terminated polyurethane, a process for its preparation and its use.
2. Discussion of the Background
In the building industry, joints serve for compensating movements between individual structural elements. Such movements are caused, for example, by thermal expansion or settling processes. As a rule, joints are sealed using sealing compounds, for example according to DIN EN ISO 1 1600. In addition to the sealing function, sealing compounds must also compensate movements due to elastic deformation. Base polymers used for the preparation of the sealing compounds are silicones, acrylates, butyl rubbers, polysulfides, polyurethanes and MS polymers. Silane-crosslinking polyurethanes are new for this application.
The reaction of secondary aminosilanes with isocyanate-containing polyurethane prepolymers leads to silane-terminated polyurethanes which can be crosslinked by means of moisture. The crosslinking of corresponding sealing compounds and adhesive materials can be accelerated by adding a catalyst.
Conventional isocyanate-containing polyurethane prepolymers are generally obtained from polyols, which are mostly synthesized from ethylene oxide and/or propylene oxide, and aliphatic or aromatic isocyanates.
The reaction of isocyanate-containing polyurethane prepolymers with aliphatic or aromatic secondary aminosilanes is catalyzed by tin compounds. The reaction gives silane-terminated polyurethanes for adhesive and sealant applications, as described, for example, in EP 0 676 403 A1.
Alternatively, isocyanatosilanes, such as, for example, OCN—(CH
2
)
3
Si(X)
3
, where X is an alkoxy group, such as methoxy or ethoxy, can also be reacted with hydroxyl-containing polyurethane prepolymers to give silane-terminated polyurethanes (U.S. Pat. No. 4,345,053). No gaseous byproduct is liberated during the silane crosslinking, compared to the case of the classical urethane crosslinking. Thus, isocyanate-free systems, such as coating compositions, finishes, adhesives and sealing compounds can be substantially safely formulated since volatile isocyanate monomers, e.g. tolylene diisocyanate (TDI), are suspected of being very harmful to health.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an improved silane-terminated polyurethane, in particular for adhesive and sealant applications.
This and other objects are achieved according to the present invention, the first embodiment of which includes an adhesive material or sealing compound, comprising: a metal-free silane-terminated polyurethane.
A further embodiment includes a method of making an adhesive material or sealing compound, comprising:
mixing a metal-free silane-terminated polyurethane polyurethane with a plasticizer and optionally a filler.
Another embodiment of the present invention includes a metal-free silane-terminated polyurethane, obtained by reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
R—NH—(CH
2
)
3
Si(R
1
)
x
(OR
2
)
(3-x)
  (Ia)
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
R—NH—CH
2
—CH(R
1
)—CH
2
—Si(R
1
)
x
(OR
2
)
(3-x)
  (Ib)
wherein in formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R
1
is a methyl group, R
2
is a methyl or ethyl group and x is 0 or 1,
with a polyurethane prepolymer in the absence of a metal catalyst;
wherein the polyurethane prepolymer has at least one terminal isocyanate group.
In yet another embodiment the present invention relates to a process for the preparation of a metal-free silane-terminated polyurethane, comprising:
reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
R—NH—(CH
2
)
3
Si(R
1
)
x
(OR
2
)
(3-x)
  (Ia)
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
R—NH—CH
2
—CH(R
1
)—CH
2
—Si(R
1
)
x
(OR
2
)
(3-x)
  (Ib)
wherein in the formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R
1
is a methyl group, R
2
is a methyl or ethyl group and x is 0 or 1:
with a polyurethane prepolymer in the absence of a metal catalyst;
wherein the polyurethane prepolymer carries at least one terminal isocyanate group.
DETAILED DESCRIPTION OF THE INVENTION
Surprisingly, it was found that the reaction of an aliphatic secondary aminosilane of formulae (Ia) or (Ib) with an isocyanate-containing polyurethane prepolymers in the absence of a metal catalyst, in particular of a tin catalyst, leads to a colorless and low-viscosity silane-terminated polyurethane:
R—NH—(CH
2
)
3
Si(R
1
)
x
(OR
2
)
(3-x)
  (Ia)
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
R—NH—CH
2
—CH(R
1
)—CH
2
—Si(R
1
)
x
(OR
2
)
(3-x)
  (Ib)
wherein in formulae (Ia) and (Ib), R is a linear or branched alkyl group having 1 to 18 C atoms, R
1
is a methyl group, R
2
is a methyl or ethyl group and x is 0 or 1.
A metal catalyst, such as, for example, dibutyltin dilaurate (DBTL), is not necessary for the present silane termination reaction. This is advantageous because the thermal cleavage of —NR—CO—NR— groups is promoted in particular by a high content of tin compounds.
According to the present invention, a low-viscosity, metal-free silane-terminated polyurethane can be formulated in a simple and economical manner with a further additive, such as a filler, a plasticizer, a thixotropic agent, a stabilizer, a pigment, etc., to give an adhesive or a sealing compounds.
In addition, the productivity of the prepolymer preparation increases due to the shorter pot lives in the silane termination reaction.
Moreover, a silane-terminated polyurethane prepared according to the present invention is particularly environmentally compatible because it is substantially free of residues of metal catalysts, i.e. metal-free.
The rapid reaction of an isocyanate group of the polyurethane prepolymer with a secondary aliphatic aminosilane of formulae (Ia) or (Ib) is preferred in the preparation of the silane-terminated polyurethane. Preferably DYNASYLAN® 1189 is used as secondary aliphatic aminosilane. The reaction proceeds according to the equation:
prepolymer-NCO+nBu—NH—(CH
2
)
3
—Si(OMe)
3
→prepolymer-NH—CO-nBuN—(CH
2
)
3
—Si(OMe)
3
.
The possible, but undesired, chain-lengthening secondary reaction—undesired because it increases the viscosity—is not observed in the process according to the invention. Thus, the chain-lengthening secondary reaction is effectively suppressed:
prepolymer-NH—CO-nBuN—(CH
2
)
3
Si(OMe)
3
+prepolymer-NCO→prepolymer-N(CO—NH-prepolymer)-CO-nBuN—(CH
2
)
3
—Si(OMe)
3
.
The present invention thus relates to a metal-free, in particular tin-free, silane-terminated polyurethane for an adhesive material or a sealing compound.
The present invention furthermore relates to a metal-free silane-terminated polyurethane which is obtained by reacting at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ia)
R—NH—(CH
2
)
3
Si(R
1
)
x
(OR
2
)
(3-x)
  (Ia)
or at least one aliphatic secondary aminoalkylalkoxysilane of formula (Ib)
R—NH—CH
2
—CH(R
1
)—CH
2
—Si(R
1
)
x
(OR
2
)
(3-x)
  (Ib)
wherein in the formulae (Ia) and (Ib), R is a linear, branched or cyclic alkyl group preferably cyclohexyl, having 1 to 18 C atoms, preferably having 1 to 6 C atoms, R
1
is a methyl group, R
2
is a methyl or ethyl group and x is 0 or 1,
with a polyurethane prepolymer having at least one terminal isocyanate group in the absence of a metal catalyst.
Preferably, the reaction of the aliphatic secondary aminoalkylalkoxysilane with the polyurethane prepolymer is carried out in the absence of a tin catalyst. Conventionally, dibutyltin dilaurate (DBTL) or another dialkyltin dicarboxylate compound is used as a tin catalyst.
Preferred secondary aminoalkylalkoxysilanes are N-(n-butyl)-3-aminopropyltrimethoxysilane, N-(n-butyl)-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropylmethyldimethoxysilane, N-(n-butyl)-3-aminopropylmethy

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