Twisted Biphenyl Diamine Accelerator for Color Stability and Stress Control
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Solution Overview
Problem
Conventional tertiary aromatic amines used in light curable compositions, especially in dental applications, suffer from color instability and high polymerization shrinkage stress, which can lead to discoloration and material damage due to their structural isomerization and fast curing rates.
Innovation Solution
The use of novel tertiary aromatic diamines with a twisted biphenyl moiety as coinitiators or accelerators, such as N,N,N',N'-tetramethyl-2,2'-trifluoro-4,4'-biphenyldiamine (TMFBP), which offer improved color stability and reduced polymerization stress by modulating photopolymerization kinetics and stress dispersion in light curable resin systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional tertiary aromatic amines (e.g., EDAB) are used as accelerators in light curable compositions, then polymerization acceleration efficiency is improved, but color stability deteriorates due to structural isomerization and discoloration
Solution Approach 1:
The patent modifies the chemical structure of conventional tertiary aromatic amines by introducing a twisted biphenyl moiety with specific substitution patterns (2,2′,6,6′-tetrasubstitute). This structural parameter change prevents planar conjugation and stabilizes the aromatic ring against UV/thermal-induced isomerization, thereby maintaining color stability while preserving the amine's accelerator function in photopolymerization
Solution Approach 2:
The invention creates a composite molecular structure combining a twisted biphenyl core with aromatic amine functional groups. This composite structure integrates the color-stabilizing twisted biphenyl framework with the polymerization-accelerating amine moieties, achieving both improved color stability and maintained accelerator efficiency
2Productivity
If fast curing rate is achieved through conventional photopolymerization, then productivity is improved, but polymerization shrinkage stress increases causing material damage
Solution Approach 1:
The patent implements a two-step light initiation process where polymerization occurs in distinct phases: an initial slower curing phase followed by a final curing phase. This periodic action allows stress relief during the intermediate stage while achieving complete cure, reducing overall shrinkage stress despite maintaining high final conversion
Solution Approach 2:
The invention modifies the polymerization kinetics by using the novel twisted biphenyl amine accelerator with camphorquinone photoinitiator, creating a controlled reaction rate profile that balances curing speed with stress development, enabling kinetic control over stress buildup
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 novel diamines provide enhanced color stability and reduced polymerization shrinkage stress, making them suitable for dental and other applications where color stability and mechanical properties are critical, while also allowing for balanced mechanical strength and handling characteristics.
Implementation Method 1
UV and visible light are two common light sources to promote such curing reaction. Furthermore such a light curing process can also be classified as photo-induced cationic polymerization or photo-induced free radical polymerization based on the nature of photo-initiator and mechanism of polymerization.
Implementation Method 2
It has been found that tertiary aromatic amines, such as Ethyl-4-DimethylAmine Benzoate (EDAB), are the most effective accelerators.
Data Source
AI summary
A photopolymerization accelerator composition improving color stability and controlling polymerization shrinkage stress of cured resin and/or the resulting composite paste thereby feature by tertiary twisted biphenyldiamine with the general formula I:R2 and R3 are each independently alkyl having from 1 to 5 carbon atoms; R and R1 are each independently hydrogen or halogen; alkyl, alkoxy, or alkylthio having from 1 to 18 carbon atoms; or phenyl and/or substituted phenyl alkoxy, or alkylthio having from 1 to 18 carbon atoms. It can be used in part with conventional photosensitizers and radically polymerizable monomers.