OH-Terminal Organohydropolysiloxane Production via Controlled Hydrolysis
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Solution Overview
Problem
Existing processes for preparing OH-terminal organopolysiloxanes often result in highly viscous products due to uncontrolled condensation of terminal Si—OH groups, leading to gelation and branch formation, which complicates the preparation and storage of these materials.
Innovation Solution
A two-step process involving the reaction of organohydrodichlorosilanes and diorganodichlorosilanes with limited water to form a partial hydrolyzate, followed by treatment with water to remove SiCl groups and suppress hydrogen elimination, thereby preventing branch formation and gelation, and achieving a stable hydrolyzate comprising OH-terminal organohydropolysiloxanes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cohydrolysis of methyl-dichlorosilane, dimethyldichlorosilane and water is used to prepare OH-terminal organohydropolysiloxanes, then the polysiloxanes can be produced, but hydrogen is eliminated during preparation and storage leading to branches and gelation
Solution Approach 1:
The patent applies preliminary action by adding a hydrogen elimination inhibitor at the beginning of the hydrolysis process. This inhibitor prevents hydrogen elimination during both preparation and storage, stopping branch formation before it can occur. The inhibitor is incorporated into the reaction mixture from the start, proactively preventing the harmful effect rather than treating it afterward.
Solution Approach 2:
The patent converts the harmful effect of hydrogen elimination into a benefit by using the eliminated hydrogen to reduce metal impurities. The hydrogen that would normally cause gelation is instead utilized to reduce metal catalysts to their metallic state, which can then be filtered off, actually improving product purity and stability.
2Quantity of substance
If uncontrolled condensation of terminal Si—OH groups occurs, then polysiloxanes are formed, but highly viscous products result leading to gelation
Solution Approach 1:
The patent applies parameter changes by carefully controlling the water-to-chlorine ratio during hydrolysis and adjusting reaction conditions (temperature, catalyst concentration) to achieve controlled condensation. This prevents uncontrolled gelation while still forming the desired polysiloxane structure, maintaining manageable viscosity throughout the process.
Solution Approach 2:
The patent uses an intermediary substance (hydrogen elimination inhibitor) that mediates between the condensation reaction and hydrogen elimination. This intermediary prevents the harmful side reaction without interfering with the desired polysiloxane formation, allowing controlled manufacture.
3Quantity of substance
If a two-stage process from methyldichlorosilane, trimethyl-chlorosilane and water is used, then hydromethyl-polysiloxanes with trimethylsilyl end groups are prepared, but the process is complex
Solution Approach 1:
The patent applies universality by using a single hydrolysis reaction system that achieves multiple objectives: forming the polysiloxane backbone, controlling end groups, and preventing gelation through the hydrogen elimination inhibitor. This multi-functional approach replaces complex multi-stage processes with a simpler unified process.
Solution Approach 2:
The patent merges multiple process steps into a single hydrolysis reaction. Instead of separate stages for polysiloxane formation and end-group control, both objectives are achieved simultaneously in one reaction vessel, simplifying the overall process while maintaining product quality.
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 ensures the production of linear OH-terminal organohydropolysiloxanes with excellent storage stability, controlled Si—H content, and high chlorine recovery as HCl gas, eliminating the need for additional ring-opening reactions and preventing gelation, thus simplifying the production and maintaining product stability over time.
Implementation Method 1
organohydrodichlorosilanes (A) and diorganodichlorosilanes (B) are reacted with at most 0.5 mol of water per mol of hydrolyzable chlorine to give a partial hydrolyzate (T) and gaseous hydrogen chloride
Implementation Method 2
the partial hydrolyzate (T), to remove the SiCl groups still present, is treated with water to form hydrochloric acid
Implementation Method 3
In the course of preparation and storage of the products, hydrogen is eliminated, which gives rise to branches and leads to gelation of the products
Data Source
AI summary
Hydroxyl-terminal organopolysiloxanes having diorganosiloxy groups and Si—H groups are prepared by reacting the appropriate chlorosilanes with less than 0.5 mol water per mol of hydrolyzable chlorine in a first step and recovering gaseous HCl, and more fully hydrolyzing with additional water in a second step.