Protected Organotin Catalysts for Polyurethane Coatings
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Solution Overview
Problem
Existing polyurethane synthesis catalysts are either not latent enough to maintain stability in the absence of oxygen or lose latency upon exposure to isocyanates, leading to reduced pot life and storage challenges, especially in coatings applications where rapid curing and low VOC levels are required.
Innovation Solution
The use of protected alpha-hydroxystannane compounds with labile protecting groups that remain stable in air and isocyanate environments for several days, becoming active only upon exposure to oxygen and alcohol, or acid, during the application process, allowing for extended pot life and rapid curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional catalysts are used to achieve rapid curing, then productivity is improved, but viscosity stability and pot life deteriorate
Solution Approach 1:
The catalyst is prepared in a protected latent form in advance, which remains stable during storage and mixing. The activation action is postponed until the moment of application when oxygen is introduced, allowing the catalyst to transform from inactive protected form to active form just before curing begins, thus maintaining viscosity stability during pot life while enabling rapid curing when needed
2Object-generated harmful factors
If solvent levels are reduced to meet environmental regulations, then VOC emissions are decreased, but pot life is shortened
Solution Approach 1:
The protected catalyst is prepared in advance in a stable latent form that can be incorporated into low-solvent formulations. The catalyst remains inactive during storage and mixing, allowing extended pot life even with reduced solvent content. Upon application and exposure to oxygen, the catalyst activates to enable curing, thus maintaining both environmental compliance and adequate working time
3Stability of the object's composition
If air-activated catalysts are used to extend pot life, then viscosity stability is improved, but the catalysts lose latency upon exposure to isocyanate
Solution Approach 1:
A protecting group acts as an intermediary between the catalyst and the reaction environment. This protecting group shields the catalyst from premature activation by isocyanate and moisture during storage and mixing. The protecting group is designed to be labile and removable under controlled conditions (such as oxygen exposure or acid treatment), allowing the catalyst to activate only when intended, thus maintaining both viscosity stability and reliable latency
Solution Approach 2:
The chemical state of the catalyst is changed by introducing a protecting group that alters its reactivity parameters. The protected catalyst exhibits different chemical properties compared to the unprotected form, specifically showing resistance to isocyanate and moisture. When the protecting group is removed or transformed (through oxygen exposure or acid treatment), the catalyst's reactivity parameters change back to the active state, enabling controlled activation while maintaining stability during storage
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 approach provides extended viscosity stability and rapid curing of polyurethane coatings, maintaining latency during storage and activating upon application, thereby enhancing productivity and reducing VOC levels in coatings systems.
Implementation Method 1
Upon exposure to air, such species oxidize to give distannoxanes, e.g. Bu2(AcO)SnOSn(OAc)Bu2, which are known to be highly active for urethane formation.
Implementation Method 2
This invention describes the use of protected alpha-hydroxystannane compounds as catalysts for formation of crosslinked polyurethanes from polyols and isocyanates.
Data Source
AI summary
This invention relates to a protected organotin-based catalyst system for polyurethane synthesis that is useful in coatings applications. The catalyst has a formula according to; R1aR2bR3cSn[CH(OX)R4]d, wherein R1, R2, and R3 are the same or different and represent an optionally substituted hydrocarbyl, aromatic, alkoxide, amide, halide or stannyl group, R4 represents an optionally substituted hydrocarbyl or optionally substituted aryl group. a, b, and c are independently 0, 1, 2, or 3; d is 1, 2 or 3; and a+b+c+d=4; and X is an acid-labile or moisture-labile protecting group. When a coating mixture comprising the catalyst is sprayed and/or applied to a substrate as a thin film in air, the catalyst is activated. For solvent-based refinish systems comprising hydroxyl and isocyanate species at high solids levels, the catalyst system therefore provides extended viscosity stability, i.e., pot life.