NCO-Terminated MDI Polyurethane: Low MDI Monomer, Stable Viscosity
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Solution Overview
Problem
Existing MDI-based NCO-terminated polyurethane compositions with low MDI monomer content exhibit high viscosity and instability over time, leading to limited shelf life and difficulty in formulation as surface coatings, adhesives, or sealants at low temperatures, and traditional stabilizing agents are ineffective or require large quantities.
Innovation Solution
Incorporating an isocyanate compound with a molar volume of less than or equal to 300 mL/mol into MDI-based NCO-terminated polyurethane compositions with an MDI content of less than or equal to 1% by weight, stabilizes viscosity without the need for large amounts of traditional stabilizing agents, allowing for stable use at low temperatures and improved mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If MDI monomer content is reduced to less than or equal to 1% by weight, then toxicity problems are reduced, but viscosity increases and stability over time deteriorates
Solution Approach 1:
The patent changes the chemical parameter by introducing compound (A) with specific molecular characteristics (molar volume ≤ 300 mL/mol, specific functional groups) to modify the physical-chemical behavior of the polyurethane composition. This compound acts as a molecular spacer or modifier that prevents excessive polymer chain association, thereby stabilizing viscosity without compromising the low MDI content formulation.
Solution Approach 2:
Compound (A) serves as an intermediary substance that mediates between the polyol and polyisocyanate components. It facilitates controlled reaction kinetics and prevents uncontrolled polymerization that would lead to viscosity increase, while itself remaining chemically stable and non-toxic at the used concentrations (0.1-5% by weight).
2Object-affected harmful factors
If MDI monomer content is reduced to less than or equal to 1% by weight, then toxicity problems are reduced, but the composition becomes difficult to formulate as surface coatings, adhesives, or sealants at low temperatures
Solution Approach 1:
The patent modifies the rheological parameters of the composition by adding compound (A), which acts as a viscosity modifier. This compound changes the flow characteristics of the polyurethane composition, enabling it to maintain appropriate viscosity for coating, adhesive, and sealant applications at low temperatures (5-35°C) without requiring high MDI content.
Solution Approach 2:
The patent introduces compound (A) with specific local molecular properties (functional groups, molar volume) that locally interact with polymer chains to reduce intermolecular forces. This creates regions of reduced viscosity within the composition, facilitating ease of application at low temperatures while maintaining overall composition integrity and low toxicity.
3Stability of the object's composition
If traditional stabilizing agents are used to reduce viscosity increase over time, then viscosity stability improves, but large quantities are required which is generally not desired
Solution Approach 1:
The patent employs compound (A) as a highly efficient stabilizing agent that, despite being used in relatively small quantities (0.1-5% by weight), provides long-term viscosity stability. The compound is specifically designed to be chemically stable and non-reactive under storage conditions, effectively replacing traditional stabilizers that would require much higher concentrations.
Solution Approach 2:
The patent changes the stabilizing mechanism by using compound (A) with specific molecular parameters (molar volume, functional groups) that provide steric hindrance and electronic stabilization. This approach achieves viscosity stability with minimal additive content, unlike traditional stabilizers that require large quantities to achieve the same effect.
Data Source
AI summary
1) A polyurethane composition comprising: a) at least 98% by weight of at least one non-hot-melt NCO-terminated polyurethane based on diphenylmethane diisocyanate (MDI), b) an MDI monomer content of 1% or less by weight, c) at least one particular isocyanate compound with a molar volume of 300 milliliters per mol or less. 2) A process for preparing a polyurethane composition as defined above, and an adhesive, sealant, and/or surface coating composition formulated from such a polyurethane composition.