Dye-linked initiators consisting of erythrosine B as a chromophore and ethyl 4-dimethylaminobenzoate as an electron donor linked by a different number of methylene units were prepared to achieve efficient photoinitiators of free radical polymerization in a visible-light region. The relative photoinitiating efficiencies of novel photoinitiators in photopolymerization of acrylates were evaluated. The results showed that the photoinitiating system composed of the dye-linked dyad with short methylene unit chain and diphenyliodonium salt exhibited a remarkable increase in the photoinitiation ability compared to unlinked three-component system. The enhancement mechanism aroused by the onium salt was investigated. These results showed that the excellent initiating efficiency of this system could be attributed to the favorable intramolecular photoinduced electron transfer and the close distance between reaction components caused by electrostatic interactions. This result demonstrated the importance and potential of the linked photoinitiator in the design of new efficient photoinitiators.
Photocatalyzed polymerization by semiconductors has recently contributed to the methods of polymer synthesis. In this work, we developed a new type of photocatalyzed polymerization with ring-opening polymerization of lactone. A complex catalyst was designed consisting of nitrogen-doped TiO2 (N–TiO2), iodonium salt (Ph2I+PF6−) and H2O. Poly(ε-caprolactone) (PCL) with a narrow molecular weight distribution was synthesized under visible light irradiation. By using electron spin resonance (ESR), in situ 1H-nuclear magnetic resonance (1H-NMR) and MALDI-TOF mass spectrometry, the mechanism studies clearly presented the reactions of the three components in the ternary catalyst. This polymerization was ruled by the route in which ε-caprolactone (ε-CL) was activated by H+. H+ was photogenerated from the oxidation reaction of H2O. Meanwhile, H+ was stabilized by the photogenerated PF6−, forming Brønsted acid H+PF6−. The relationship between the monomer conversions and PCL molecular weights was studied.
Li Ming,Zhang Li-fen,Tao Mei-xia,Cheng Zhen-ping,Zhu Xiu-lin
In this work, a fluorescent monomer 2-(9-carbazolyl) ethyl vinyl ether (CEVE) was synthesized in our lab, and its photo-induced living cationic copolymerization behavior with isobutyl vinyl ether (IBVE) was investigated in detail using diphenyliodonium chloride (DPICl)/2,2-dimethoxy-2-phenylacetophenone (DMPA) and zinc bromide (ZnBr 2 ) initiating system in dichloromethane solution at 5 °C, −5 °C, and −15 °C, respectively. The living nature of this copolymerization system was confirmed by adding fresh comonomer method after the copolymerization almost finished. In addition, the obtained fluorescent copolymer poly(IBVE- co -CEVE) has a low glass transition temperature ( T
g ), below −10 °C.
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