Polysulfide Synthesis via Sulfur Oxidation
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Solution Overview
Problem
Conventional methods for preparing mercapto-terminated polysulfides often result in the formation of unwanted by-products, such as inorganic salts and reactive polysulfides, making it difficult to achieve high yields and suitable chain lengths for sealant applications, and are not compatible with oxidative curing systems.
Innovation Solution
The oxidation of bismercaptodiether with elemental sulfur in the presence of a base and a protic solvent, specifically an alcoholic solvent like methanol, improves selectivity towards linear di-sulfides, which are more suitable for sealant applications, by controlling reaction conditions like molar ratios, temperature, and atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional condensation polymerization is used to prepare polysulfides, then polysulfide polymers can be synthesized, but salt waste is produced which is undesired
Solution Approach 1:
The patent converts the harmful salt waste by-product of conventional condensation polymerization into a beneficial process by using oxidative polymerization with sulfur as the oxidizing agent. This approach eliminates salt formation while producing the desired polysulfide polymers through oxidation of thiol groups, transforming a harmful process into a clean synthesis method.
Solution Approach 2:
The patent changes the fundamental reaction parameters from condensation polymerization (using dihalides and alkali metal salts) to oxidative polymerization (using sulfur as oxidizing agent). This parameter change fundamentally alters the process chemistry, eliminating salt waste while maintaining polysulfide polymer production capability.
2Loss of substance
If hydroxyalkyl-terminated polysulfides are prepared by reacting with formaldehyde, then salt-free process is achieved, but the resulting polysulfides cannot be applied in oxidative curing systems
Solution Approach 1:
The patent changes the terminal group parameter from hydroxyalkyl to mercapto (thiol) by controlling the oxidation process. This parameter change enables the polysulfide to be compatible with oxidative curing systems while maintaining the salt-free process advantage. The mercapto-terminated polysulfides can undergo oxidative curing to form crosslinked networks.
3Adaptability or versatility
If mercapto-terminated polysulfides are prepared by transforming hydroxy end-groups, then oxidative curing compatibility is achieved, but chain scission risk is high and inorganic salts must be washed out
Solution Approach 1:
The patent performs preliminary oxidation of the bismercaptoether with sulfur to form the mercapto-terminated polysulfide directly, avoiding the need to transform hydroxy end-groups later. This preliminary action establishes the mercapto terminal groups before any potential chain scission could occur during subsequent transformations, and eliminates the need to wash out inorganic salts from the transformation process.
4Productivity
If oxidation of bismercaptoethers is performed without protic solvent, then reaction can proceed, but selectivity towards linear di-sulfides is poor and multiple polysulfide structures are formed
Solution Approach 1:
The patent introduces a protic solvent (such as water or alcohol) as an intermediary medium in the oxidation reaction. This intermediary facilitates the formation of linear di-sulfides by controlling the reaction environment, enabling selective oxidation while maintaining reaction efficiency. The protic solvent acts as a mediator that directs the oxidation pathway towards the desired linear structure.
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 effectively produces linear di-sulfides with improved flexibility and handling properties, reducing the formation of unwanted by-products and enabling their use in oxidative curing systems, thus enhancing the application properties of polysulfides in sealants and other materials.
Implementation Method 1
The oxidation of bismercaptoethers (like the one of formula 1 below) can result in many different polysulfides
Data Source
AI summary
Process for the preparation of polysulfide of formula (I) HS—(CH2)n—O—(CH2)m—O—(CH2)p—[S—S—CH2)nO—(CH2)m—O—(CH2)p]q—SH (I) wherein m is an integer in the range 1 to 4, n and p are integers in the range 1-10, and q is an integer in the range 1-60, by oxidizing a bismercaptodiether compound of formula (II) HS—(CH2)n—O—(CH2)m—O—(CH2)p—SH (II) with elemental sulfur in the presence of a base and a protic solvent. This process has a high selectivity towards linear disulfides.