Alkoxy-Functional Organohydrogensiloxane Oligomer Preparation
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Solution Overview
Problem
Current methods for preparing alkoxy-functional hydrogensiloxane oligomers result in products containing acetoxy groups, which increase viscosity over time and affect the stability of polymethoxy-functional polydimethylsiloxane, and lack high yield and selectivity to the beta-isomer.
Innovation Solution
A method involving the reaction of a polyorganohydrogensiloxane oligomer with an aliphatically unsaturated alkoxysilane in the presence of a platinum group metal catalyst and a hydro(acyloxy)-functional silicon compound, followed by treatment with a sorbent and distillation to produce an acetoxy-free alkoxy-functional organohydrogensiloxane oligomer with high selectivity to the beta-isomer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If dimethylacetoxysilane is used as a hydrosilylation reaction promoter to improve yield and regioselectivity, then the yield increases from 40% to 75% and beta-isomer selectivity increases from 70% to 88%, but acetoxy groups are bonded to silicon atoms in the final product causing viscosity to increase with time
Solution Approach 1:
The patent removes the harmful acetoxy groups from the final product through purification steps (distillation and treatment with water or ammonium hydroxide solution) after the hydrosilylation reaction. This extraction of the harmful component allows the product to achieve both high yield and viscosity stability, resolving the contradiction between improved productivity and maintained stability.
Solution Approach 2:
The patent utilizes the acetoxy groups formed during the reaction as intermediate species that can be easily removed through simple purification steps. The presence of acetoxy groups during the reaction phase actually facilitates the formation of the desired beta-isomer, and their subsequent removal through distillation or treatment with water/ammonium hydroxide yields the stable final product without compromising the high yield achieved during synthesis.
2Ease of manufacture
If conventional purification steps are omitted, then the process is simpler and faster, but acetoxy groups remain in the product causing viscosity increase over time
Solution Approach 1:
The patent employs distillation under reduced pressure or treatment with water/ammonium hydroxide solution to remove acetoxy groups. These parameter changes (pressure reduction, temperature control, chemical treatment) enable efficient removal of harmful components while maintaining product integrity, achieving both ease of manufacture and viscosity stability through optimized purification parameters.
3Device complexity
If the reaction is performed without a promoter, then the process is simpler, but the yield is low (40%) and beta-isomer selectivity is poor (70%)
Solution Approach 1:
The patent introduces dimethylacetoxysilane as an intermediary promoter that facilitates the hydrosilylation reaction between tris(dimethylsiloxy)-n-propylsilane and vinyltrimethoxysilane. This intermediary substance mediates the reaction to proceed with high efficiency, achieving 75% yield and 88% beta-isomer selectivity while maintaining reasonable process complexity through a well-defined catalytic system.
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 method achieves high yield and selectivity to the beta-isomer, reducing acetoxy content and viscosity stability issues, resulting in a more stable alkoxy-functional organohydrogensiloxane oligomer suitable for forming polyalkoxy-functional polyorganosiloxanes for condensation reaction curable compositions.
Implementation Method 1
reacting starting materials comprising: (A) a polyorganohydrogensiloxane oligomer of unit formula (I): (HR12) where R1 is independently a monovalent hydrocarbon group, (B) an aliphatically unsaturated alkoxysilane, (C) a hydrosilylation reaction catalyst, and (D) a hydro(acyloxy)-functional silicon compound
Implementation Method 2
treating the reaction product with a sorbent
Implementation Method 3
distilling the product, thereby recovering the alkoxy-functional organohydrogensiloxane oligomer
Data Source
AI summary
A method for the preparation of an alkoxy-functional hydrogensiloxane oligomer includes reacting a polyorganohydrogensiloxane oligomer and an aliphatically unsaturated alkoxysilane in the presence of a hydrosilylation reaction and a promoter. The resulting crude reaction product is treated with a treating agent, and thereafter distilled to produce the alkoxy-functional organohydrogensiloxane oligomer. The alkoxy-functional hydrogensiloxane oligomer can be reacted with polyorganosiloxane having an aliphatically unsaturated monovalent hydrocarbon group to form a polyalkoxy-functional polyorganosiloxane. The polyalkoxy-functional polyorganosiloxane can be formulated in condensation reaction curable compositions.