Mixed Silane-Terminated Polymers via Segmented Reaction
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Solution Overview
Problem
Existing methods for producing silane-terminated polymers, such as those used in coatings and adhesives, face challenges with high viscosity due to broad molecular weight distribution and poor reproducibility, requiring additional steps and costly NCO-containing alkoxysilanes, which complicates the process and increases costs.
Innovation Solution
A process involving the simultaneous reaction of polyol hydroxyl groups with diisocyanate and isocyanatosilane in the presence of a catalyst, followed by reaction with an aminosilane, to produce mixed silane-terminated polymers with both urea and urethane-linked silane groups, achieving a narrow molecular weight distribution and low viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If amino-functional alkoxysilanes are reacted with NCO-containing prepolymers to form alkoxy-functional polyurethanes, then the polymers crosslink quickly and cure to non-sticky materials with good strength and ductility, but the polymers exhibit high viscosity which complicates formulation
Solution Approach 1:
The invention segments the silane termination into two distinct pathways: (1) formation of urea-linked silane groups through reaction of NCO groups with amino-functional alkoxysilanes, and (2) formation of urethane-linked silane groups through reaction of remaining NCO groups with hydroxy-functional prepolymers. This segmentation allows control over molecular weight distribution and prevents excessive chain extension that would increase viscosity, while still achieving the desired crosslinking strength through the urea groups.
Solution Approach 2:
The invention changes the reaction parameters by controlling the stoichiometry and sequence of additions. Specifically, the ratio of amino-functional to hydroxy-functional prepolymers is optimized, and the reaction is conducted in a controlled manner to ensure complete consumption of NCO groups without excessive chain extension. This parameter optimization maintains low viscosity while achieving adequate crosslinking.
2Stability of the object's composition
If NCO-containing alkoxysilanes are reacted with hydroxy-functional prepolymers to form urethane groups, then the silane group is linked to the polymer, but the NCO-containing alkoxysilanes have limited shelf life and are expensive
Solution Approach 1:
The invention uses isocyanate groups as an intermediary species. Instead of using unstable NCO-containing alkoxysilanes directly, the process generates isocyanate groups in situ from the reaction of diisocyanate with polyol, which then react with amino-functional prepolymers. This intermediary approach allows the use of stable, shelf-stable starting materials while achieving the desired silane linkage.
Solution Approach 2:
The invention performs preliminary formation of the polyol-diisocyanate prepolymer before adding the amino-functional prepolymer. This preliminary action ensures that the NCO groups are generated at the appropriate stage and in the correct quantity, eliminating the need to store unstable NCO-containing alkoxysilanes and reducing overall process cost.
3Adaptability or versatility
If a multi-step process is used to combine both synthesis routes, then the disadvantages of individual routes are overcome, but the process has insufficient reproducibility due to difficult control of reactions
Solution Approach 1:
The invention ensures continuous consumption of NCO groups through sequential addition of amino-functional and then hydroxy-functional prepolymers. This continuous action prevents side reactions and ensures complete conversion, improving reproducibility. The process is designed so that each step naturally drives the reaction to completion without requiring complex control measures.
Solution Approach 2:
The invention incorporates feedback control by monitoring the consumption of NCO groups and adjusting the addition rates accordingly. The amino-functional prepolymer is added first to consume available NCO groups, followed by hydroxy-functional prepolymer to consume remaining NCO groups. This feedback-driven sequential addition ensures consistent results and improves manufacturing precision.
4Productivity
If the reaction of free NCO groups with excess hydroxyl groups is difficult to control, then incomplete conversion occurs and unwanted pre-elongation may occur, but this leads to broadening of molecular weight distribution and increase in viscosity
Solution Approach 1:
The invention applies partial action by using a stoichiometric amount of amino-functional prepolymer that is slightly in excess relative to the available NCO groups. This ensures complete consumption of NCO groups without significant pre-elongation. The controlled excess prevents unwanted side reactions while maintaining high reaction efficiency and narrow molecular weight distribution.
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
This process simplifies the production of silane-terminated polymers with low viscosity, improving processability and reducing costs by eliminating the need for plasticizers and minimizing reaction steps, while maintaining excellent long-term stability and suitability as moisture-curing adhesives.
Implementation Method 1
simultaneous reaction of the hydroxyl groups of a polyol component A) with at least one diisocyanate B) and at least one isocyanatosilane C), in the presence of at least one catalyst D)
Implementation Method 2
in the presence of at least one catalyst D)
Implementation Method 3
subsequent reaction of the free NCO groups of the reaction product from step a) with an aminosilane E)
Data Source
AI summary
The invention relates to a method for preparing a silane-terminated polymer by reacting a polyol A) with a diisocyanate B), an isocyanatosilane C) and an amino silane E), wherein the polyol component A) is reacted simultaneously with a mixture of at least one diisocyanate B) and one isocyanatosilane C), and the resulting product is subsequently reacted with the amino silane E) to produce the silane-terminated polymer. The method according to the invention can be used to prepare mixed silane-terminated polymers having a low viscosity.