Expandable mixtures that are devoid of isocyanates
Foamable mixtures of excellent quality and which are isocyanate free are prepared from silane-terminated prepolymers in which a proportion of the silane end groups are replaced by non-polar organic groups. As a result, the prepolymers have much greater hydrocarbon blowing agent compatibility.
1. An isocyanate-free foamable mixture comprising:
(A) a mixture of prepolymers in which 50-99% of the chain ends are terminated by alkoxysilyl groups and 1-50% of the chain ends are terminated by groups of the formula [2]
A 1 -R 1 [2]
where
A 1 is an oxygen atom, an N—R 2 group or a sulfur atom wherein when A 1 is NR 2 or oxygen,
A 1 is part of a urea or urethane group, respectively,
R 1 is an alkyl, cycloalkyl, alkenyl, aryl or arylalkyl radical having 2-50 carbon atoms in which the carbon chain is optionally interrupted by nonadjacent oxygen atoms, sulfur atoms or N—R 2 groups, and the carbon chain of R 1 is optionally substituted by lateral alkyl groups having 1-10 carbon atoms or halogen atoms, and
R 2 is a hydrogen atom or an alkyl, alkenyl or aryl radical having 1-10 carbon atoms, and
(B) a hydrocarbon blowing agent.
2. The foamable mixture of claim 1 , wherein A 1 is oxygen or NR 2 and is part of a urethane group.
3. The foamable mixture of claim 1 , wherein A 1 is NR 2 and A 1 is part of a urea group.
4. The foamable mixture of claim 1 , wherein from 65-95% of the prepolymer chain ends are terminated by alkoxysilyl groups and 5-35% of the prepolymer chain ends are terminated by groups of the formula [2].
5. The foamable mixture of claim 1 , wherein from 80-95% of the prepolymer chain ends are terminated by alkoxysilyl groups and 5-20% of the prepolymer chain ends are terminated by groups of the formula [2].
6. The mixture of claim 1 , comprising prepolymers which have alkoxysilyl groups of the formula [3]
where
A 2 is an oxygen atom, an N—R 5 group or a sulfur atom,
R 3 is an alkyl, cycloalkyl, alkenyl or aryl radical having 1-10 carbon atoms,
R 4 is an alkyl radical having 1-2 carbon atoms or an ω-(oxyalkyl)alkyl radical having a total of 2-10 carbon atoms,
R 5 is a hydrogen atom, an alkyl, alkenyl or aryl radical having 1-10 carbon atoms, or a —CH 2 —SiR 3 z (OR 4 ) 3-z group and,
z is 0, 1 or 2.
7. The mixture of claim 1 , wherein the hydrocarbon blowing agent (B) comprises one or more hydrocarbons having 1-5 carbon atoms.
8. The mixture of claim 1 , comprising a blowing agent mixture which comprises at least 50% by volume of hydrocarbon blowing agent (B) and one or more further blowing agents.
9. The mixture of claim 8 , wherein a further blowing agent is dimethyl ether.
10. A process for preparing a foamable mixture of claim 1 , wherein the prepolymer (A) is prepared at least partly in a pressure vessel.
11. A pressure vessel containing a foamable mixture of claim 1 .
12. An isocyanate-free foamable mixture comprising:
(A) a mixture of prepolymers in which 50-99% of the chain ends are terminated by moisture condensable alkoxysilyl groups and 1-50% of the chain ends are terminated by groups of the formula [2]
A 1 -R 1 [2]
where
A 1 is an oxygen atom, an N—R 2 group or a sulfur atom,
R 1 is an alkyl or alkenyl group having 10-18 carbon atoms and
R 2 is a hydrogen atom or an alkyl, alkenyl or aryl radical having 1-10 carbon atoms, and
(B) a hydrocarbon blowing agent.