Thiol-ene Stabilizer Using Phenolic and Phosphite Inhibitors
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Solution Overview
Problem
Thiol-ene compositions face challenges in achieving long-term shelf stability and maintaining low viscosity during storage due to spontaneous dark reactions, with existing stabilizers like N-PAL being carcinogenic and other systems presenting drawbacks such as viscosity increase and stability issues.
Innovation Solution
An inhibitor system comprising substituted benzene or naphthalene compounds with hydroxyl and alkoxy groups, acidic compounds with a pKa between 1 and 3, and phosphites or phosphonites, which effectively stabilizes thiol-ene compositions by preventing spontaneous polymerization and maintaining low viscosity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional phenolic inhibitors like p-methoxy phenol are used to stabilize thiol-ene compositions, then shelf stability is improved to some extent, but the amount is limited for applications such as gel nails and long-term stability is not achieved
Solution Approach 1:
The patent combines multiple inhibitor compounds with different chemical structures and mechanisms of action (phenolic compounds, aromatic amines, carboxylic acids) to create a composite inhibitor system. This synergistic combination provides superior long-term shelf stability while remaining compatible with various thiol-ene applications including gel nails, coatings, and adhesives.
Solution Approach 2:
The patent optimizes the concentration ranges of each inhibitor component and their ratios to achieve maximum stability. By carefully controlling the parameters of inhibitor composition and dosage, the system provides extended shelf life while maintaining compatibility across different applications.
2Ease of operation
If thiol-ene compositions are stored at room temperature, then ease of operation is maintained, but spontaneous dark reactions occur leading to polymerization and viscosity increase
Solution Approach 1:
The inhibitor system is designed to preemptively counteract spontaneous dark reactions before they can cause significant polymerization. The multiple inhibitor compounds work together to scavenge radicals and prevent chain reactions, maintaining composition stability during storage at convenient room temperatures.
3Reliability
If stabilizers like N-PAL are used to prevent spontaneous polymerization, then shelf stability is improved, but carcinogenicity issues arise
Solution Approach 1:
The patent replaces long-lived carcinogenic stabilizers with a system of organic inhibitor compounds that provide equivalent stabilization functionality without toxic effects. These organic inhibitors achieve the necessary shelf stability through synergistic action rather than relying on persistent carcinogenic substances.
Solution Approach 2:
The patent converts the potential harm of spontaneous polymerization into a controlled process by using inhibitor compounds that safely manage radical reactions. The system transforms the destabilizing dark reactions into manageable processes that do not compromise stability or safety.
4Reliability
If phosphines are used as stabilizers, then shelf stability is improved, but Michael-addition between thiol groups and acrylate functionalities occurs leading to viscosity increase
Solution Approach 1:
The patent uses inhibitor compounds that act as intermediaries to prevent direct Michael-addition between thiol and acrylate groups. These inhibitors interfere with the harmful reaction pathway while allowing the desired thiol-ene polymerization to proceed when initiated, thus maintaining viscosity 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 proposed inhibitor system ensures long-term shelf stability and low viscosity of thiol-ene compositions at both room and elevated temperatures, while maintaining high reactivity and producing 3D objects with low shrinkage and high notch impact strength.
Implementation Method 1
All thiol-ene reactions exhibit spontaneous dark reactions, yielding polymers (oligomers) in the absence of an initiator unless an efficient inhibitor is being added
Implementation Method 2
They have one drawback though: it is difficult to stabilize them, especially to attain long-term shelf stability
Data Source
AI summary
The present invention relates to stabilizers for thiol-ene compositions and to radiation curable thiol-ene compositions based thereon. Such radiation curable compositions can advantageously be used in inks, overprint varnishes, coatings, adhesives, for the making of 3D objects and for the making of solder resist and gel nails. Provided in particular is an inhibitor system (I) for thiol-ene compositions based on —at least one inhibitor compound (i) having a % DPPH radical scavenging activity of at least 90%, the inhibitor compound (i) being selected from substituted benzene compounds or substituted naphthalene compounds containing at least two substituents selected from the group consisting of hydroxyl groups and C1-C3 alkoxy groups bonded directly to the benzene or the naphthalene ring, —at least one acidic compound (ii) having a pKa between 1 and 3, and —at least one compound (iii) selected from the group consisting of phosphites and phosphonites, with the proviso that if the inhibitor compound (i) is a substituted benzene that it contains at least two hydroxyl groups bonded directly to the benzene ring. Also provided is an inhibitor system (II) for thiol-ene compositions based on that is based on —at least one inhibitor compound (i) having a % DPPH radical scavenging activity of at least 90%, the inhibitor compound (i) being selected from substituted benzene compounds or substituted naphthalene compounds containing at least two substituents selected from the group consisting of hydroxyl groups and C1-C3 alkoxy groups bonded directly to the benzene or the naphthalene ring, —at least one compound (iv) selected from the group consisting of spirophosphites, and —optionally, at least one acidic compound (ii) having a pKa between 1 and 3, and with the proviso that if the inhibitor compound (i) is a substituted benzene that it contains at least two hydroxyl groups bonded directly to the benzene ring.