HEUR thickener and process for its preparation
The present invention is a process for preparing an aqueous solution of a hydrophobically modified alkylene oxide poly(urethane-urea-allophanate) thickener by contacting isocyanate reactive groups with a stoichiometric excess of a diisocyanate, followed by reaction with water. The thickener surprisingly shows a maintenance or improvement in hiding in paint formulations while maintaining other critical rheological properties.
1. A process for preparing an aqueous solution of a hydrophobically modified alkylene oxide poly(urethane-urea-allophanate) thickener consisting of the steps of: a) contacting under reactive conditions 1) a water-soluble polyalkylene glycol; 2) a hydrophobic capping agent or a hydrophobic difunctional agent or a combination thereof; and 3) a 2 to 50 percent stoichiometric excess of a diisocyanate with respect to the sum of the moles of isocyanate reactive groups of the polyalkylene glycol; and ii) the capping agent or the hydrophobic difunctional agent or a combination thereof, to form a polyurethane prepolymer with isocyanate functionality; then b) contacting the prepolymer with water under conditions sufficient to convert the prepolymer to an aqueous solution of a hydrophobically modified alkylene oxide poly(urethane-urea-allophanate).
2. The process of claim 1 wherein the polyalkylene glycol is a polyethylene glycol, the diisocyanate is 1,6-hexamethylene diisocyanate, isophorone diisocyanate, or 4,4′-methylenebis(isocyanatocyclohexane.
3. The process of claim 2 wherein the diisocyanate is used at a 5 to 35 percent stoichiometric excess with respect to the sum of the moles of isocyanate reactive groups of the polyalkylene glycol and the capping agent, wherein the polyalkylene glycol is a polyethylene glycol having a M w in the range of 4000 to 10,000 Daltons; and the hydrophobic agent is a hydrophobic capping agent.
4. The process of claim 3 wherein the hydrophobic capping agent is an alcohol or a tertiary aminoalcohol.
5. The process of claim 4 wherein equivalent ratio of the polyalkylene glycol to the alcohol or tertiary amino alcohol is from 2:1 to 10:1.
6. The process of claim 5 wherein equivalent ratio of the polyalkylene glycol to the alcohol or tertiary amino alcohol is from 3.5:1 to 6.5:1, wherein the hydrophobic capping agent is a tertiary aminoalcohol.
7. The process of claim 5 wherein the hydrophobically modified alkylene oxide poly(urethane-urea-allophanate) further includes primary amine end groups or biuret branch points in the polymer backbone or a combination thereof.
8. The process of claim 1 wherein the polyalkylene glycol, the diisocyanate, and the hydrophobic capping agent or the hydrophobic difunctional agent or a combination thereof are contacted simultaneously under reaction conditions to form the polyurethane prepolymer with isocyanate functionality.
9. The process of claim 1 wherein the polyalkylene glycol and the diisocyanate are first contacted with each other under reaction conditions to form a first prepolymer intermediate, which is then contacted with the hydrophobic capping agent or the hydrophobic difunctional agent or a combination thereof under reaction conditions to form a second prepolymer intermediate, which is then contacted with water to form the aqueous solution of a hydrophobically modified alkylene oxide poly(urethane-urea-allophanate).
10. A process for preparing an aqueous solution of a hydrophobically modified alkylene oxide poly(urethane-urea-allophanate) thickener comprising the steps of: a) contacting under reactive conditions and in the presence of a bismuth octoate catalyst 1 ) a water-soluble polyalkylene glycol; 2) a hydrophobic capping agent or a hydrophobic difunctional agent or a combination thereof; and 3) a 2 to 50 percent stoichiometric excess of a diisocyanate with respect to i) the sum of the moles of isocyanate reactive groups of the polyalkylene glycol; and ii) the capping agent or the hydrophobic difunctional agent or a combination thereof, to form a polyurethane prepolymer with isocyanate functionality; then b) contacting the prepolymer with water under conditions sufficient to convert the prepolymer to an aqueous solution of a hydrophobically modified alkylene oxide poly(urethane-urea-allophanate).
11. The process of claim 10 wherein the polyalkylene glycol is a polyethylene glycol, the diisocyanate is 1,6-hexamethylene diisocyanate, isophorone diisocyanate, or 4,4′-methylenebis(isocyanatocyclohexane.
12. The process of claim 10 wherein the diisocyanate is used at a 5 to 35 percent stoichiometric excess with respect to the sum of the moles of isocyanate reactive groups of the polyalkylene glycol and the capping agent, wherein the polyalkylene glycol is a polyethylene glycol having a M w in the range of 4000 to 10,000 Daltons; and the hydrophobic agent is a hydrophobic capping agent.
13. The process of claim 12 wherein the hydrophobic capping agent is an alcohol or a tertiary aminoalcohol.
14. The process of claim 13 wherein equivalent ratio of the polyalkylene glycol to the alcohol or tertiary amino alcohol is from 2:1 to 10:1.
15. The process of claim 14 wherein equivalent ratio of the polyalkylene glycol to the alcohol or tertiary amino alcohol is from 3.5:1 to 6.5:1, wherein the hydrophobic capping agent is a tertiary aminoalcohol.
16. The process of claim 15 wherein the hydrophobically modified alkylene oxide poly(urethane-urea-allophanate) further includes primary amine end groups or biuret branch points in the polymer backbone or a combination thereof.
17. The process of claim 10 wherein the polyalkylene glycol, the diisocyanate, and the hydrophobic capping agent or the hydrophobic difunctional agent or a combination thereof are contacted simultaneously under reaction conditions to form the polyurethane prepolymer with isocyanate functionality.