Isocyanate Stability via Silane Catalyst Deactivation
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Solution Overview
Problem
Existing processes for producing liquid isocyanate mixtures containing carbodiimide (CD) and/or uretonimine (UI) groups face challenges with stability, color retention, and pressure buildup due to incomplete stopping of phospholine catalysis, leading to unsatisfactory storage stability and color issues in polyisocyanates and prepolymers.
Innovation Solution
A process involving partial carbodiimidization of organic isocyanates with phospholine oxide catalysts, followed by stopping the reaction using organic silanes of the formula HnSiX4-n, where n is 1 to 3 and X is a saturated or unsaturated organic radical, particularly phenyl, to achieve stable and low-color isocyanate mixtures that can be converted into prepolymers with improved storage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If phospholine oxide catalyst is used to initiate carbodiimidization reaction under gentle temperature conditions, then the reaction can proceed at low temperature, but the catalyst cannot be effectively stopped leading to continued reaction, gas release, and pressure buildup during storage
Solution Approach 1:
A silane compound is introduced as an intermediary substance to stop the phospholine oxide catalyst. The silane reacts with the catalyst to form a stable complex, effectively deactivating it and preventing further carbodiimidization reaction during storage, thus solving the storage stability problem while maintaining low reaction temperature
Solution Approach 2:
The invention changes the chemical state of the catalyst by introducing silane, transforming it from an active catalytic state to an inactive complexed state. This parameter change in catalyst activity stops the reaction progression and prevents gas release and pressure buildup during storage
2Reliability
If silylated acid or strong acid is used to stop phospholine catalysis, then the reaction can be stopped, but the resulting isocyanates and prepolymers have significantly increased color numbers and poor color stability
Solution Approach 1:
The invention uses silane compounds as a disposable stopping agent that reacts with and deactivates the catalyst without introducing chromophoric groups. The silane-catalyst complex is stable and does not contribute to color formation, unlike silylated acids or strong acids which leave residual species that increase color numbers
Solution Approach 2:
The invention converts the potential harm of having an active catalyst during storage into a benefit by using silane to deliberately deactivate the catalyst in a controlled manner. This controlled deactivation prevents unwanted side reactions and color formation, turning the catalyst's reactivity from a harmful factor into a manageable parameter
3Reliability
If non-silylated acid or acid chloride is used to stop the catalyst, then the reaction can be stopped, but the catalyst becomes active again when exposed to temperature during storage or processing
Solution Approach 1:
The silane compound performs a preliminary action by reacting with and deactivating the phospholine oxide catalyst before storage or further processing. This preliminary deactivation ensures that the catalyst remains inactive under subsequent temperature variations, preventing reactivation and maintaining long-term stability
Solution Approach 2:
The invention provides beforehand cushioning against temperature-induced reactivation by using silane to form a stable complex with the catalyst. This complex is thermally stable and prevents the catalyst from becoming active again during storage or processing, cushioning against potential instability
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 process results in isocyanate mixtures and prepolymers with enhanced storage stability, low color numbers, and minimal change in NCO content and viscosity, addressing the limitations of previous methods by effectively stopping the carbodiimidization reaction and preventing gas release and color deterioration.
Implementation Method 1
a starting isocyanate, which is an organic isocyanate or a mixture of several organic isocyanates, with a catalyst K of the formula cyclo-C4H6P(O)R is partially carbodiimidized
Implementation Method 2
the carbodiimidization reaction in a Temperature ≤ 80 °C is stopped by adding a stopper, where the stopper is an organic silane S of the general formula HnSiX4-n
Data Source
AI summary
The invention relates to a process for preparing liquid, storage-stable isocyanate mixtures having carbodiimide (CD) and/or uretonimine (UI) groups or prepolymers derived therefrom, wherein (i) in a first step a starting isocyanate which is an organic isocyanate or a mixture of two or more organic isocyanates is partly carbodiimidized with a catalyst K of the formula cyclo-C4H6P(O)R where the substituent R is a saturated or unsaturated, optionally substituted, especially halogen-substituted, organic radical, and then (ii) in a second step the carbodiimidization reaction is stopped at a temperature of ≤ 80°C by adding a stopper, the stopper used being an organic silane S of the general formula HnSiX4 - n where n is a natural number in the range from 1 to 3, where X is a saturated or unsaturated, optionally substituted, especially halogen-substituted, organic radical.