Moisture-Crosslinkable Polyimine Sealants Without Aldehyde Release
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Solution Overview
Problem
Aldimines, particularly aromatic aldimines, release volatile and odorous aldehydes during crosslinking, which is undesirable in adhesive compositions based on moisture-crosslinkable polyurethanes and epoxides.
Innovation Solution
A moisture-crosslinkable sealant composition comprising polyurethane P with NCO end functions and polyimine A, formed through a reaction between a (poly)urethane-aldehyde and a primary diamine, or a dihydroxyaldimine with a (poly)isocyanate, optionally with additional monoamine or monoisocyanate, to avoid aldehyde release.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aldimines are used as moisture-activatable curing agents in polyurethane-based systems, then crosslinking can be achieved without CO2 formation, but volatile and odorous aldehydes are released during hydrolysis
Solution Approach 1:
The invention changes the chemical structure parameter of the aldimine by using cyclic aliphatic aldehydes instead of aromatic or linear aliphatic aldehydes. This structural modification maintains the crosslinking functionality while eliminating the harmful volatile aldehyde release during hydrolysis, as the cyclic structure prevents complete decomposition to volatile products
Solution Approach 2:
The invention creates a composite curing system combining polyurethane with cyclic aliphatic aldimine crosslinking agents. This composite approach integrates the moisture-activatable crosslinking mechanism with a structurally modified aldimine that provides both the desired crosslinking performance and the elimination of harmful aldehyde emissions
2Strength
If aromatic aldimines are used for crosslinking, then effective curing is achieved, but strong odors and volatile aldehyde release occur
Solution Approach 1:
The invention fundamentally changes the aromatic structure parameter to a cyclic aliphatic structure. This parameter change eliminates the characteristic strong odors and volatility associated with aromatic aldimines while preserving the crosslinking strength through the maintained molecular weight and functional group reactivity of the cyclic structure
3Productivity
If direct crosslinking of isocyanate groups with moisture is used, then crosslinking occurs rapidly, but CO2 is released causing bubble formation
Solution Approach 1:
The invention introduces cyclic aliphatic aldimine as an intermediary blocking agent that reacts with isocyanate groups to form stable adducts. This intermediary mechanism prevents direct reaction between isocyanate and moisture that would produce CO2, while still enabling subsequent crosslinking through controlled hydrolysis of the aldimine adducts without gas evolution
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 composition effectively crosslinks without releasing aldehydes, providing a stable and odor-free adhesive solution for sealants and coatings.
Implementation Method 1
On contact with water, (poly)aldimines can hydrolyse to the corresponding amines and aldehydes
Implementation Method 2
Aldimines are condensation products of primary polyamines and aldehydes
Data Source
AI summary
The present invention relates to a moisture-crosslinkable sealant composition comprising:at least one polyurethane P comprising at least two NCO end functions;at least one polyimine A obtained via a process comprising a step of reaction between at least:a) a (poly)urethane-aldehyde comprising at least 2 aldehyde functions;b) a primary diamine;c) optionally in the presence of a primary monoamine or a monoaldehyde if the —CHO/NH2 molar ratio is other than 1.