Initial compounds for producing polyurethanes
The invention relates to starting compounds which can be used for the preparation of polyurethanes and can be prepared by reaction of hydroxyl-containing oligomers of formaldehyde.
1. A polyurethane prepolymer which is prepared by reaction of hydroxyl groups of an oligomer of formaldehyde represented by formula (I)
with an isocyanate,
wherein n is an integer from 2 to 19.
2. The polyurethane prepolymer as claimed in claim 1 wherein an NCO content is in a range from 10 to 30% by weight of the polyurethane prepolymer weight.
3. The polyurethane prepolymer as claimed in claim 1 wherein an NCO content is in a range from 15 to 25% by weight of the polyurethane prepolymer weight.
4. A process for preparing polyurethanes, which comprises reacting compounds as claimed in claim 1 with compounds having at least two groups which are reactive toward isocyanates.
5. The polyurethane prepolymer as claimed in claim 1 , wherein the oligomer of formaldehyde represented by formula (I) is obtained by a process comprising distillation of a solution wherein formaldehyde and oligomers of formaldehyde are in equilibrium.
6. The polyurethane prepolymer as claimed in claim 5 , wherein the process comprising distillation of a solution wherein formaldehyde and oligomers of formaldehyde are in equilibrium is thin film evaporation.
7. The polyurethane prepolymer as claimed in claim 5 , wherein the oligomer of formaldehyde represented by formula (I) is a fraction of oligomers having narrow molecular weight distribution obtained from the distillation of the solution wherein formaldehyde and oligomers of formaldehyde are in equilibrium.
8. The polyurethane prepolymer as claimed in claim 1 , wherein
a hydroxyl number of the oligomer of formaldehyde represented by formula (I) is in a range of 1436 mg KOH/g to 389 mg KOH/g.
9. The polyurethane prepolymer as claimed in claim 1 , wherein the isocyanate is an isocyanate having two or more isocyanate groups.
10. The polyurethane prepolymer as claimed in claim 9 , wherein the isocyanate is an aliphatic isocyanate, an aromatic isocyanate or a modified isocyanate.
11. The polyurethane prepolymer as claimed in claim 10 , wherein the isocyanate is an aliphatic isocyanate being hexamethylene diisocyanate or isophorone diisocyanate.
12. The polyurethane prepolymer as claimed in claim 10 , wherein the isocyanate is an aromatic isocyanate selected from the group consisting of tolylene diisocyanate, diphenylmethane diisocyanate, and a mixture of diphenylmethane diisocyanate and polymethylenepolyphenylene polyisocyanates.
13. The polyurethane prepolymer as claimed in claim 10 , wherein the isocyanate is a modified isocyanate which has been modified by incorporation of one group selected from the groups consisting of a uretdione, an isocyanurate, an allophanate and an uretonimine.