Polyurethanes made using zinc catalysts
Polyisocyanate-based polymers are formed by curing a reaction mixture containing at least one polyisocyanate and at least one isocyanate-reactive compound having at least two isocyanate-reactive groups in the presence of a zinc catalyst that contains at least one zinc atom associated with a polydentate ligand that contains at least one nitrogen-containing complexing site.
1. A process for preparing a polyisocyanate-based polymer, comprising forming a reaction mixture containing at least one polyisocyanate, at least one isocyanate-reactive compound having at least two isocyanate-reactive groups and at least one zinc catalyst, and then curing the reaction mixture to form a polymer, wherein the zinc catalyst contains at least one zinc atom associated with a polydentate organic ligand that contains at least two complexing sites, of which at least one is nitrogen-containing, wherein the ligand compound is
a β-imino alcohol or enol.
2. The process of claim 1 wherein the ligand compound has either of structures III or V
wherein R 5 is a group that is bonded to the indicated nitrogen atom through a carbon, oxygen, nitrogen or silicon atom and each R 1 , R 2 and R 3 is independently hydrogen or a group that is bonded to the indicated carbon atom through a carbon, oxygen, nitrogen or silicon atom, provided that any two or more of R 1 , R 2 and R 3 may together form a divalent or trivalent group that is bonded to the indicated carbon atoms through carbon, oxygen, nitrogen and/or silicon atoms, and further provided that an R 3 and an R 5 group may together form a divalent group that is bonded to the indicated carbon atom and the indicated nitrogen atom though carbon, oxygen, nitrogen and/or silicon atoms.
3. The process of claim 2 , wherein each R 5 group is a hydrocarbyl group that is unsubstituted, inertly substituted, or substituted with one or more complexing sites, or a hydroxyl, an ether group, or a primary, secondary or tertiary amino group.
4. The process of claim 3 wherein each R 1 , R 2 and R 3 is independently hydrogen or a hydrocarbyl group that is unsubstituted, inertly substituted, or substituted with one or more complexing sites.
5. The process of claim 1 wherein the polyisocyanate-based polymer is a polyurethane, polyurea, or polyurethane-urea.
6. The process of claim 1 , wherein the reaction mixture further contains a blowing agent and a surfactant, and the polyisocyanate-based polymer is a foam.
7. The process of claim 1 , wherein the isocyanate-reactive compound includes a polyol having a molecular weight of from 800 to 12,000 and an average of from 1.8 to 2.5 hydroxyl groups per molecule, and the polyisocyanate-based polymer is a cast elastomer.
8. The process of claim 1 wherein the reaction mixture contains at least one additional catalyst.