Vinylpolymerisation. 281. Mitt

Ohne Zusammenfassung     

Studies directed toward the total synthesis of the rubradirin antibiotics. 4. A new Diels-Alder—Claisen effective diene

A new diene has been synthesized which effectively couples the Diels-Alder reaction with the Claisen rearrangement.     

Synthesis of functionalized asymmetric star polymers containing conductive polyacetylene segments by living anionic polymerization

Novel 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE asymmetric star polymers comprising the conductive polyacetylene precursor, poly(4-methylphenyl vinyl sulfoxide) (PMePVSO), and other segments, such as polystyrene, poly(alpha-methylstyrene), poly(4-methoxystyrene), poly(4-trimethylsilylstyrene), and poly(4-methylstyrene), were synthesized by the methodology based on living anionic polymerization using DPE-functionalized polymers. This methodology involves the addition reaction of a DPE-functionalized polymer to a living anionic polymer followed by the living anionic polymerization of MePVSO initiated from the in situ formed polymer anion with two, three, or four polymer segments. The resultant asymmetric star polymers possessed predetermined molecular weights, narrow molecular weight distributions (Mw/Mn < 1.03), and desired compositions as confirmed by SEC, 1H NMR, SLS, and elemental analysis. After thermal treatment, the PMePVSO segment in the star polymer could be completely converted into a conductive polyacetylene segment, evident from TGA and elemental analysis. These asymmetric star polymers are expected to exhibit interesting solution properties and unique microphase-separated morphological suprastructures with potential applications in nanoscopic conductive materials. Moreover, this methodology can afford the target asymmetric star polymers with arm segments varying in a wide range and enables the synthesis of more complex macromolecular architectures.     

Incomplete fusion of the 16O + 27Al reaction

Velocity spectra of fusion-like residues produced in the reactions of 90 MeV and 150 MeV ¹⁶O with ²⁷Al were measured. At 90 MeV the velocity spectra were well reproduced by a statistical model calculation. At 150 MeV the observed centroids of the velocity spectra deviate from the statistical model predictions. The centroid shifts as a function of the atomic and mass numbers of evaporation residues were analyzed by two different model calculations based on the assumption that incomplete fusion is (a) a peripheral process, or (b) independent on the angular momentum of the entrance channel, respectively. The later assumption is in better agreement with the presented data.     

Nanoparticle preparation of quinacridone and β-carotene using near-infrared laser ablation of their crystals

Quinacridone nanoparticles with a mean size of about 200 nm are successfully prepared using nanosecond near-infrared (NIR) laser ablation of its microcrystalline powders in heavy water. The absorption spectra of the formed colloidal solutions depend on the excitation wavelengths, which is eventually ascribed to number and energy of absorbed photons. β-carotene has low photostability and is easily decomposed upon UV/VIS laser ablation of its solid, while its nanoparticles are prepared utilizing this NIR laser ablation technique. The advantage of nanoparticle preparation by NIR laser ablation is discussed.