期刊
POLYMER CHEMISTRY
卷 9, 期 1, 页码 38-47出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c7py01590a
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资金
- Ivoclar Vivadent AG
- NAWI Graz
- Austrian Science Fund (FWF) [I 1614] Funding Source: researchfish
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-pi* 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 alpha-cleavage of the acylgermanes react remarkably fast with monomers. Addition rate constants to (meth) acrylates range from 0.4-4.5 x 10(8) 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.
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