Dual-Cure Polythioether Composition for Dark-Zone Sealant Curing
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Solution Overview
Problem
Existing polythioether polymer compositions face limitations in achieving rapid and efficient curing, especially in areas without direct light exposure, and struggle to balance low glass transition temperature with high fuel resistance properties for applications like aircraft and automobile sealants.
Innovation Solution
The development of dual cure compositions comprising a dithiol monomer, diene monomer, radical cleaved photoinitiator, peroxide, and amine as a peroxide-amine redox initiator, which can be cured by actinic radiation and propagate dark cure mechanisms, allowing for rapid curing and maintaining low glass transition temperatures while providing high fuel resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If radiation curing is used to achieve rapid curing, then curing speed is improved, but curing in dark zones becomes insufficient
Solution Approach 1:
The patent combines radiation curing and dark cure mechanisms into a dual-cure system. The composition includes photoinitiators for radiation-induced curing and peroxide-amine redox initiators for dark cure. This merging allows the sealant to cure rapidly under light exposure while simultaneously maintaining curing capability in dark zones through the peroxide-amine redox mechanism, resolving the contradiction between curing speed and curing completeness.
Solution Approach 2:
The patent uses a composite curing system with multiple initiator types (photoinitiators and peroxide-amine redox initiators) and multiple curing mechanisms (radiation curing and dark cure). This composite approach enables the composition to exhibit both rapid radiation-induced curing in exposed areas and reliable dark cure in unexposed areas, achieving both high speed and high reliability.
2Temperature
If glass transition temperature is reduced to maintain flexibility, then low temperature performance is improved, but fuel resistance deteriorates
Solution Approach 1:
The patent employs a composite polymer system combining polythioether polymers with specific glass transition temperatures and crosslinking agents. This composite structure allows the base polymer to provide low glass transition temperature for flexibility while the crosslinking network (formed through dual-cure mechanism) provides the dense structure necessary for fuel resistance, thus resolving the contradiction between low-temperature performance and fuel resistance.
Solution Approach 2:
The patent optimizes the chemical structure and crosslinking density of the polymer system to achieve a balance between glass transition temperature and fuel resistance. By controlling the composition ratios and crosslinking degree, the patent creates a material that maintains adequate flexibility (glass transition temperature below -50°C) while achieving excellent fuel resistance through the dense crosslinked network.
3Reliability
If dual cure mechanism is implemented to improve curing completeness, then curing reliability is improved, but composition complexity increases
Solution Approach 1:
The patent designs the peroxide-amine redox initiator system to serve multiple functions: it acts as a dark cure initiator, provides catalytic activity for crosslinking, and maintains stability during storage. This multi-functionality reduces the need for separate additives and simplifies the overall composition while achieving reliable dual-cure performance.
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 dual cure mechanism enables rapid curing within seconds, even in dark zones, achieving 90% or greater conversion up to 5 cm in under 20 seconds, and results in polythioether polymers with glass transition temperatures below -50°C and excellent jet fuel resistance, suitable for demanding applications like aircraft and automobile sealants.
Implementation Method 1
a) a dithiol monomer; b) a diene monomer; c) a radical cleaved photoinitiator... In some embodiments, the composition may be cured by application of light from an actinic light source
Implementation Method 2
d) a peroxide; and e) an amine; where the peroxide and amine together are a peroxide-amine redox initiator... propagate dark cure mechanisms
Data Source
Figure 1
AI summary
Compositions that are curable to polythioether polymers are provided, comprising: a) a dithiol monomer; b) a diene monomer; c) a radical cleaved photoinitiator; d) a peroxide; and e) an amine; where the peroxide and amine together are a peroxide-amine redox initiator. In some embodiments, the amine is a tertiary amine. In some embodiments, the amine is selected from the group consisting of dihydroxyethyl-p-toluidine, N,N-diisopropylethylamine, and N, N, N', N", N"-pentamethyl-diethylenetriamine. In some embodiments, the peroxide is selected from the group consisting of di-tert-butyl peroxide, methyl ethyl ketone peroxide, and benzoyl peroxide. In some embodiments, the composition may additionally comprise a polythiol monomer having three or more thiol groups.