Dual-Cure Polysiloxane Compositions for Thick-Layer Sealing
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Solution Overview
Problem
Existing organo(poly)siloxane compositions face challenges with uneven curing rates due to moisture diffusion limitations in thick layers and the need for toxic catalysts, especially in applications requiring rapid adhesion or sealing, while radiation-curable systems suffer from slow curing in shadow areas without catalysts.
Innovation Solution
Development of organo(poly)siloxanes containing both moisture- and radiation-crosslinkable groups in a single molecule, eliminating the need for catalysts and ensuring rapid curing across thick layers and shadow areas through a free-radical-induced thiol-ene crosslinking mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If moisture-curing organo(poly)siloxane preparations are used, then the curing reaction can proceed without radiation exposure, but the curing rate becomes dependent on water diffusion through the surface and cannot achieve rapid curing within thick layers
Solution Approach 1:
The patent combines moisture-curing and radiation-curing mechanisms into a single organo(poly)siloxane composition. The composition contains both hydrolyzable groups (for moisture crosslinking) and polyunsaturated radicals (for radiation crosslinking), allowing the material to cure rapidly under radiation while also maintaining the ability to cure through moisture diffusion in thick layers.
Solution Approach 2:
The invention creates a composite crosslinking system where two different crosslinking mechanisms (moisture-based and radiation-based) operate simultaneously or sequentially within the same material matrix. This composite approach allows the material to overcome the limitations of each individual mechanism.
2Speed
If trialkoxysilyl-functional acrylic derivatives are added to achieve rapid moisture crosslinking, then the curing speed increases, but toxic tin compound catalysts are required which raise toxicological concerns
Solution Approach 1:
The patent removes the toxic catalyst component from the system by using organo(poly)siloxanes with inherent reactivity toward moisture. The hydrolyzable groups in the siloxane structure can react with ambient moisture without requiring external catalysts, thereby eliminating the toxicological concerns associated with tin compounds.
Solution Approach 2:
The organo(poly)siloxane composition is designed to be self-curing through its inherent chemical structure. The hydrolyzable groups and polyunsaturated radicals enable the material to crosslink automatically upon exposure to moisture or radiation, without needing external catalysts or additives.
3Speed
If radiation-curable organo(poly)siloxane mixtures are used, then rapid curing is achieved under direct radiation, but curing progresses only slowly in shadow areas
Solution Approach 1:
The patent merges radiation-curing and moisture-curing capabilities in a single composition. The presence of both polyunsaturated radicals (for radiation crosslinking) and hydrolyzable groups (for moisture crosslinking) ensures that areas exposed to radiation cure rapidly while shadow areas continue to cure through moisture diffusion, achieving uniform overall curing.
4Object-affected harmful factors
If separate polymers with aliphatically unsaturated radicals and thiol functions are produced, then moisture crosslinking can occur without catalysts, but the production complexity and cost-effectiveness are reduced
Solution Approach 1:
The patent combines multiple functional groups (hydrolyzable groups, polyunsaturated radicals, and thiol functions) within a single organo(poly)siloxane molecule or copolymer structure. This eliminates the need to produce and handle multiple separate polymers, simplifying production while maintaining the ability to crosslink without catalysts.
5Speed
If long-chain carboxylic acids are used as catalysts for moisture crosslinking, then crosslinking can be accelerated, but corrosive properties and adverse effects on storage stability occur leading to hydrogen evolution and safety risks
Solution Approach 1:
The patent eliminates the need for carboxylic acid catalysts by using organo(poly)siloxanes with hydrolyzable groups that can react with moisture inherently. This removal of catalysts prevents the corrosive effects, hydrogen evolution, and storage stability problems associated with long-chain carboxylic acids.
Solution Approach 2:
The organo(poly)siloxane composition performs self-crosslinking through its inherent chemical structure without requiring external catalysts. The hydrolyzable groups and polyunsaturated radicals enable automatic crosslinking upon exposure to moisture or radiation, ensuring both speed and storage stability.
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 solution provides storage-stable organo(poly)siloxane compositions that cure rapidly and uniformly, avoiding catalyst-related issues and ensuring effective adhesion and sealing in various applications without migration of uncrosslinked constituents.
Implementation Method 1
organo(poly)siloxane compositions that, in addition to acrylic functional units, also have hydrolyzable groups, such as alkoxy radicals
Implementation Method 2
free-radical-induced thiol-ene crosslinking
Data Source
AI summary
An organo(poly)siloxane (A) consists of units of general formula (I) RnSiO(4-n/2), where R is selected from the radicals R1, —OR2, Ru, RS and Q, wherein R1 denotes a monovalent substituted or unsubstituted hydrocarbon radical having 1 to 18 carbon atoms, R2 denotes a hydrogen atom or a monovalent substituted or unsubstituted hydrocarbon radical having 1 to 6 carbon atoms, Ru denotes a monovalent aliphatic unsaturated hydrocarbon radical having 2 to 18 carbon atoms, RS denotes a monovalent thiol-functionalized hydrocarbon radical, Q is a nitrogen functional group of formula (II) —CR5R6—NR4R3, where R3 and R4 each independently denote hydrogen or a substituted or unsubstituted hydrocarbon radical, and R5 and R6 each independently denote hydrogen or the methyl radical. The organo(poly)siloxane (A) contains per molecule at least one unit of general formula (III) Q-Si(OR7)2O1/2, at least 1 aliphatically unsaturated radical Ru, and at least 2 thiol-functionalized groups RS.