The invention relates to alkoxysilane groups comprising prepolymers and the use thereof as binding agents for sealants. More specifically the invention relates to alkoxysilyl polyurethanes prepared from a polyol having a number-average molecular weight of from greater than 20,000 to 30,000 and an isocyanate alkoxysilane.
1. An alkoxysilane-group-modified polyurethane obtained by reacting
C) 1.0 eq of a polyol component having a number-average molecular weight of from greater than 20,000 g/mol to 30,000 g/mol, comprising one or more polyoxyalkylene polyols or polyoxyalkylene polyol prepolymers and
D) 0.80 to 1.20 eq of a compound of formula (I) comprising isocyanate and alkoxysilane groups
wherein
X, Y, Z
are, independently of one another, linear, cyclic or branched C 1 -C 8 alkyl or C 1 -C 8 alkoxy radicals, wherein at least one of the radicals is a C 1 -C 8 alkoxy group, and X, Y or Z are optionally, independently of one another, bridged, and
R
is any at least difunctional organic radical,
and wherein the polyethers used in A) have a content of terminal unsaturation of less than 0.02 meq/g and a polydispersity of less than 1.5.
2. The alkoxysilane-group-modified polyurethane of claim 1 , wherein X, Y and Z in formula (I) are, independently of one another, a methoxy or ethoxy group and R is a methylene or propylene radical.
3. The alkoxysilane-group-modified polyurethane of claim 1 , wherein only polyoxyalkylene polyols having a number-average molecular weight of from 21,000 g/mol to 25,000 g/mol are used in A).
4. The alkoxysilane-group-modified polyurethane of claim 1 , wherein 0.90 to 1.10 eq of component B) are used.
5. The alkoxysilane-group-modified polyurethane of claim 1 , wherein any remaining free NCO groups are further reacted by means of an allophanatisation reaction.
6. A low-modulus sealant comprising the alkoxysilane-group-modified polyurethane of claim 1 .
7. A polymer obtained by crosslinking the alkoxysilane groups of the polyurethanes of claim 1 .
8. A preparation comprising
from 10 weight % to 100 weight % of at least one alkoxysilane-group-modified polyurethane of claim 1 ;
from 0 weight % to 30 weight % of a plasticiser or a mixture of several plasticisers;
from 0 weight % to 5 weight % of a moisture stabiliser or a mixture of several moisture stabilisers;
from 0 weight % to 5 weight % of a UV stabiliser or a mixture of several UV stabilisers;
from 0 weight % to 5 weight % of a catalyst or a mixture of several catalysts; and
from 0 weight % to 80 weight % of a filler or a mixture of several fillers,
wherein the preparation has a modulus at 100% elongation of a maximum of 0.4 N/mm 2 determined according to ISO 11600.
9. The alkoxysilane-group-modified polyurethane of claim 1 , wherein R is a straight-chain, branched or cyclic alkylene radical having 1 to 8 carbon atoms.
10. The preparation of claim 8 , wherein said preparation comprises a maximum of 25 weight % of a plasticiser.
11. The preparation of claim 8 , wherein said preparation comprises a maximum of 20 weight % of a plasticiser.