Tin (IV) Chelate Catalysts for Polyurethane Stability
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Solution Overview
Problem
Existing tin catalysts for polyurethane synthesis are susceptible to hydrolysis, leading to instability and variable activity, especially under humid conditions, and are not suitable for use with aliphatic polyols without risking alcoholysis.
Innovation Solution
A tin catalyst with a specific structure, including anionic ligands, polydentate chelating ligands with phenoxy and amine/imine groups, which provides thermolatent properties and stability against moisture, maintaining constant activity across wide temperature ranges and varying moisture contents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional tin catalysts (tin alkoxides, tin carboxylates) are used for polyurethane synthesis, then catalytic activity is achieved, but the catalysts are susceptible to hydrolysis by moisture in the air, leading to instability and variable activity
Solution Approach 1:
The patent introduces phenoxy ligands as intermediary groups that mediate between the tin center and the reaction environment. These phenoxy ligands form a protective coordination sphere around the tin atom, acting as a buffer that prevents direct interaction between moisture and the reactive tin center, thereby reducing hydrolysis while maintaining catalytic activity
Solution Approach 2:
The patent creates composite catalyst structures by combining tin centers with phenoxy ligands containing amine/imine groups. This composite structure integrates multiple functional elements: the tin center provides catalytic activity, the phenoxy groups provide stability against hydrolysis, and the amine/imine groups provide additional coordination and thermolatent properties. The synergistic combination resolves the contradiction between activity and stability
2Object-affected harmful factors
If low-toxic tin (II) carboxylates are used to reduce toxicity, then toxicity issues are mitigated, but these catalysts are easily oxidized and hydrolyzed by moisture in the air
Solution Approach 1:
The patent changes the chemical parameters of the ligand system by introducing phenoxy groups with amine/imine functionalities. This parameter change transforms the catalyst from being susceptible to oxidation and hydrolysis to being resistant, while maintaining low toxicity. The phenoxy ligands create a more stable coordination environment that prevents both oxidation of the tin center and hydrolysis by moisture
Solution Approach 2:
The patent applies local quality enhancement by specifically designing the ligand structure to provide protective properties at the molecular level. The phenoxy groups with amine/imine groups create a localized protective environment around the tin center, providing resistance to oxidation and hydrolysis at the critical interface where these reactions would occur, while the overall catalyst structure maintains low toxicity
3Duration of action of moving object
If thermolatent catalysts based on tetravalent tin compounds with alkoxy or amino alcohol ligands are used, then long pot lives are achieved, but these catalysts are highly susceptible to hydrolysis by moisture and alcoholysis by aliphatic polyols
Solution Approach 1:
The patent converts the potential harm of moisture and polyol contact into a benefit by designing phenoxy ligands that are specifically resistant to hydrolysis and alcoholysis. Instead of avoiding these environmental factors, the catalyst is designed to thrive in their presence. The phenoxy groups with amine/imine groups create a stable coordination sphere that actually benefits from the reaction environment while maintaining long pot life
Solution Approach 2:
The patent changes the chemical parameters of the ligand from alkoxy or amino alcohol groups to phenoxy groups containing amine/imine functionalities. This parameter change fundamentally alters the catalyst's interaction with moisture and polyols, transforming it from being susceptible to hydrolysis and alcoholysis to being resistant, while preserving the thermolatent properties and long pot life
4Productivity
If catalysts with high activity towards aliphatic isocyanates are used, then synthesis efficiency is improved, but these catalysts show increased tendency to gelation in polyurethane synthesis
Solution Approach 1:
The patent applies local quality differentiation by designing the ligand structure to provide different properties at different locations: the phenoxy groups provide stability and control gelation tendency, while the amine/imine groups provide high catalytic activity towards aliphatic isocyanates. This spatial and functional differentiation allows the catalyst to simultaneously achieve high productivity and controlled gelation
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 catalyst exhibits improved stability and activity, reducing the risk of hydrolysis and alcoholysis, resulting in better-defined polymer structures, controlled polymerization, and improved characteristics of the resulting polyurethane products.
Implementation Method 1
a tin catalyst for the polyaddition reaction of polyisocyanates with NCO-reactive compounds, especially polyols
Implementation Method 2
The catalysts according to the invention contain tin in a tetravalent oxidation state and have a structure according to formula (I), wherein X1 represents an anionic ligand, and L1 represents a polydentate chelating ligand
Data Source
AI summary
A tin catalyst for polyurethane synthesis has a structure according to the following formula (I): SnX1n1X2n2(L1)n3(L2)n4 (I) whereby: each X1 and each X2 independently of each other stands for an anionic ligand, in particular a monovalent anionic ligand, especially selected from halides, hydroxides, oxygen, sulfur, alcoholates, thiolates and/or carboxylates, optionally with a saturated or unsaturated, cyclic or acyclic, branched or unbranched, substituted or unsubstituted hydrocarbon residue, whereby the hydrocarbon residues may be interrupted by heteroatoms; n 1 and n2 independently of each other is 0, 1 or 2; especially the sum of n 1 and n2 is 0, 1 or 2; each L1 and each L2 independently of each other stand for a polydentate chelating ligand having form 6-50 carbon atoms, and at least one phenoxy group forming a covalent Sn-O bond, especially 2, 3 or 4 phenoxy groups each forming a covalent Sn-O bond; at least one amine and/or imine group, in particular forming a coordination bond with Sn, especially 2 amine and/or imine group each forming a coordination bond with Sn; n3 is 1 or 2 and n4 is 0, 1 or 2; and whereby X1, X2, L1 and L2 are chemically different from each other.