From mono- to tetraacylgermanes: extending the scope of visible light photoinitiators
| Autor: | Iris Lamparth, Hilde Freißmuth, Judith Radebner, David E. Fast, Georg Gescheidt, Anna Eibel, Paul Faschauner, Eduard Stadler, Michael Haas, Norbert Moszner, Ana Torvisco, Harald Stueger |
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| Rok vydání: | 2018 |
| Předmět: |
Materials science
Polymers and Plastics 010405 organic chemistry CIDNP business.industry Radical Organic Chemistry Radical polymerization Bioengineering 010402 general chemistry Photochemistry 01 natural sciences Biochemistry Photobleaching 0104 chemical sciences chemistry.chemical_compound Monomer Reaction rate constant chemistry Optoelectronics Reactivity (chemistry) business Visible spectrum |
| Zdroj: | Polymer Chemistry. 9:38-47 |
| ISSN: | 1759-9962 1759-9954 |
| DOI: | 10.1039/c7py01590a |
| Popis: | We have investigated the inititiaton efficiency of carefully selected germanium-based photointiators for radical polymerization. To establish a systematic relationship between structure and reactivity, we have developed a convenient synthetic protocol for the preparation of a trisacylgermane, closing the gap from mono- to tetraacylgermane photoinitiators. The studied acylgermanes display distinct, wavelength-dependent photobleaching upon irradiation up to 470 nm. In particular, tetraacylgermanes featuring ortho-alkyl substituents reveal red-shifted n–π* bands, in line with excellent photobleaching upon visible light irradiation. Quantum yields of decomposition (determined at 385 nm) have been found to be highest for bisacylgermanes. Germyl radicals produced upon triplet-state α-cleavage of the acylgermanes react remarkably fast with monomers. Addition rate constants to (meth)acrylates range from 0.4–4.5 × 108 M−1 s−1, depending on the substitution pattern. These values are clearly higher than those reported for related phosphorus-centered radicals derived from acylphosphane oxides. We have further established the nature of the products and side-products formed at initial stages of the polymerizations using chemically induced dynamic nuclear polarization (CIDNP) experiments. |
| Databáze: | OpenAIRE |
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