Acyl Germanium Photoinitiators for Deep Curing
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Solution Overview
Problem
Current photoinitiators for visible light curing of radically polymerizable materials often result in incomplete curing due to limitations such as strong coloration and increased layer thickness, particularly in dental applications, and are either expensive or cause discoloration in final products.
Innovation Solution
Development of multifunctional aromatic acyl germanium and acyl tin compounds with specific chemical structures that can be synthesized using aromatic trisacyl metal enolates, allowing for deeper curing depths and reduced discoloration, characterized by high extinction coefficients and ease of production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If camphorquinone/amine photoinitiator system is used for visible light curing, then polymerization can be initiated, but strong yellow coloration occurs in the cured material
Solution Approach 1:
The patent modifies the molecular structure of acyl germanium compounds by introducing specific aromatic substituents and adjusting the germanium coordination environment, which shifts the absorption maximum to longer wavelengths (400-450 nm) and reduces the extinction coefficient, thereby minimizing yellow discoloration while maintaining polymerization initiation capability
Solution Approach 2:
The patent employs readily available starting materials such as aromatic acid chlorides and metal enolates that can be obtained from conventional chemical suppliers, enabling cost-effective synthesis of novel photoinitiators without requiring expensive or specialized reagents
2Manufacturing precision
If UV light is used for curing, then small layer thickness can be cured effectively, but complete curing is not possible with greater layer thicknesses
Solution Approach 1:
The patent shifts the photoinitiation wavelength from UV to visible light range (400-450 nm) by designing acyl germanium compounds with appropriate HOMO-LUMO energy gaps, enabling deeper light penetration and more uniform curing throughout thicker layers while maintaining effective polymerization initiation
Solution Approach 2:
The patent develops photoinitiators that can effectively initiate polymerization across a broad spectrum of visible light wavelengths (400-450 nm), making the curing system adaptable to different light sources and applicable to various layer thicknesses, from thin coatings to thicker dental restorations
3Productivity
If existing visible light photoinitiators are used, then polymerization can occur, but discoloration occurs in the final product
Solution Approach 1:
The patent optimizes the molecular structure of acyl germanium compounds by controlling the number and type of aromatic substituents, which tunes the absorption characteristics to have lower extinction coefficients in the visible range, reducing yellow discoloration while preserving polymerization initiation efficiency
Solution Approach 2:
The patent combines aromatic acyl germanium compounds with specific polymerizable monomers and fillers to create composite dental materials that achieve both effective curing and minimal discoloration, leveraging the synergistic effects of the photoinitiator system with the material composition
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
These compounds enable effective polymerization with longer-wave visible light, allowing for larger curing depths without significant discoloration and are cost-effective, making them suitable for various applications including dental materials.
Implementation Method 1
When irradiated with UV or visible light, the photoinitiator absorbs the light and forms the polyreaction-initiating species
Implementation Method 2
In the event of radical photopolymerization these are free radicals
Implementation Method 3
Norrish type I photoinitiators form free radicals by unimolecular bond cleavage
Implementation Method 4
Norrish type II photoinitiators undergo a bimolecular reaction, wherein in the excited state the photoinitiator reacts with a second molecule, the so-called coinitiator, and forms the polymerization-initiating radicals by electron and proton transfer
Data Source
AI summary
Compounds according to general formula (I)in which M is Ge or Sn, RAr isR1, R2, R3, R4, R5, independently of one another in each case, are —H, —F, —Cl, —OR6, —SR6, —N(R6)2, —CF3, —CN, —NO2, —COOR6, —CONHR6, a branched, cyclic or preferably linear C1-20 alkyl, C2-20 alkenyl, C1-20 alkyloxy or a C2-20 alkenoxy radical, which can be interrupted one or more times by O, S or —NR6— and substituted by one or more polymerizable groups and/or radicals R6, R6 is H, a branched, cyclic or preferably linear C1-20 alkyl or C2-20 alkenyl radical, R7 is a chemical bond, an n-valent aromatic radical or a branched, cyclic or preferably linear C1-20 alkylene radical, which can be interrupted one or more times by O, S or —NR6— and substituted by one or more polymerizable groups, ═O and/or radicals R6, n is 2 or 3 and m is 0 or 1. The compounds are particularly suitable as photoinitiators for radical polymerization and in particular for the production of dental materials.