HEUR Polymer pKa Tuning for Paint Viscosity Stability
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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, which affects the stability and performance of coatings.
Innovation Solution
Development of hydrophobically modified alkylene oxide urethane polymers with pendant or end-capping tertiary amine groups having a pKa range of 4.5 to 6.5, which provides stability across a wide pH range and resistance to heat aging, using mono- or dihydroxyalkylated dibenzylamine groups or monobenzyldi(alkyleneoxy)amino groups as hydrophobic modifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If amine-modified HEURs with higher pKa are used, then the polymer provides good associative thickening at high pH, but the viscosity decreases over time and during heat aging due to pH lowering
Solution Approach 1:
The patent changes the pKa parameter of the amine groups from higher values (comventional HEURs) to a specific range of 4.5 to 6.5. This parameter modification allows the polymer to maintain associative thickening capability across a wider pH range, including lower pH conditions that occur during heat aging, thereby preventing viscosity decrease and improving time stability.
2Stability of the object's composition
If the pH of the formulation decreases over time and heat aging, then the formulation becomes more stable in terms of pH control, but the viscosity decreases due to loss of associative thickening
Solution Approach 1:
The patent applies preliminary anti-action by selecting amine groups with pKa values of 4.5 to 6.5, which are low enough to remain protonated and active even when the formulation pH decreases during storage and heat aging. This preliminary selection of appropriate pKa values prevents the loss of associative thickening capability before it can occur, counteracting the harmful effect of pH lowering.
3Adaptability or versatility
If amine-modified HEURs are used to control viscosity through pH trigger, then the polymer provides good rheology control, but the polymer becomes sensitive to pH changes leading to poor formulation stability
Solution Approach 1:
The patent modifies the pKa parameter of the amine groups to fall within the specific range of 4.5 to 6.5. This parameter change optimizes the balance between pH responsiveness and formulation stability, allowing the polymer to respond to pH changes within the operational range of paint coatings while resisting the harmful effects of pH lowering during storage and application.
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 polymers maintain desired viscosity in coatings over a wide pH range and exhibit improved heat aging stability compared to higher pKa amine-modified HEURs, ensuring consistent performance and stability in paint formulations.
Implementation Method 1
When the pH of the HEUR composition is sufficiently low with respect to the pKa of the incorporated base, the basic groups are protonated and the viscosity is relatively low; when the pH is sufficiently high, associative thickening occurs.
Implementation Method 2
when the pH is sufficiently high, associative thickening occurs
Implementation Method 3
the basic groups are protonated and the viscosity is relatively low; when the pH is sufficiently high, associative thickening occurs
Implementation Method 4
ethylene oxide urethane polymers modified with hydrophobes that contain organic bases such as secondary or tertiary amines (amine-modified HEURs)
Data Source
AI summary
The present invention relates to a composition comprising a hydrophobically modified alkylene oxide urethane polymer with pendant or end-capping tertiary amine groups, the conjugate acids of which have a pKa in the range of about 4.5 to about 6.5. The composition of the present invention is useful as a rheology modifier for paint formulations formulated over a wide pH range and is more stable to heat aging than higher pKa amine-modified HEURs.