Guanidine-Modified HEUR Polymers for pH-Stable Viscosity
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Solution Overview
Problem
Amine-modified hydrophobically modified ethylene oxide urethane polymers (HEURs) are sensitive to pH changes in paint formulations, leading to a decrease in viscosity over time and heat aging, resulting in a poorer formulation performance.
Innovation Solution
A stable aqueous dispersion of hydrophobically modified alkylene oxide urethane polymers with endcapping tertiary amine groups, characterized by specific chemical structures and preparation methods, is developed to maintain viscosity across a wide pH range, using a compound formula and reaction scheme involving diisocyanates and water-soluble polyalkylene glycols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If amine-modified HEUR polymers are used to provide pH-triggered viscosity control, then viscosity control through pH trigger is achieved, but the formulation becomes sensitive to pH changes over time and heat aging
Solution Approach 1:
The patent changes the chemical parameter of the hydrophobe from a conventional amine (with pKa around 9-10) to a guanidine derivative (with pKa around 12-13). This parameter change in basicity allows the polymer to maintain associative thickening at higher pH values, preventing the viscosity loss that occurs when conventional amine-modified HEURs are exposed to pH-lowering mechanisms over time and heat aging.
2Ease of operation
If conventional amine-based hydrophobes are used, then associative thickening occurs at high pH, but viscosity decreases when pH drops below critical level
Solution Approach 1:
The invention changes the pKa parameter of the basic group from conventional amine levels (9-10) to guanidine levels (12-13). This elevated pKa ensures that the basic groups remain unprotonated and capable of associative thickening even when the formulation pH drops during storage and heat aging, thereby maintaining viscosity stability throughout the product lifecycle.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively preserves the desired viscosity of paint formulations during pH-lowering mechanisms, demonstrating improved heat age stability with reduced viscosity drop compared to conventional thickeners, similar to commercial rheology modifiers without contributing volatile organic compounds (VOCs).
Implementation Method 1
when the pH is sufficiently high, associative thickening occurs. Thus, incorporation of basic hydrophobes into the HEUR polymer allows relatively high concentration of polymer to be dissolved in water at low pH; once the solution is added to the high pH environment of paint coatings, the base is deprotonated and the associative thickening mechanism activated.
Data Source
AI summary
The present invention relates to a compound characterized by the following formula:wherein each R1 is independently methyl or ethyl; and n 1 to 10. The compound is useful in preparing hydrophobically modified alkylene oxide urethane polymers, which are useful as rheology modifiers for coatings formulations.