排序方式: 共有6条查询结果,搜索用时 15 毫秒
1
1.
Tetsufumi Takamoto Patrick Kerep Hiroshi Uyama Shiro Kobayashi 《Macromolecular bioscience》2001,1(6):223-227
Lipase‐catalyzed intermolecular transesterification between two different polyesters has been carried out using in toluene. The transesterification of poly(ε‐caprolactone) (PCL) and (1,4‐butylene adipate) took place via catalysis of lipase from Candida antarctica to give an ester copolymer. 13C NMR analysis showed that the resulting polymer was not a mixture of the starting polyesters, but a copolymer consisting of both units. The reaction temperature and solvent amount greatly affected the microstructure of the ester copolymer. Under appropriate conditions, the random copolymer was formed. The enzymatic transesterification has been monitored by size exclusion chromatography (SEC) and 13C NMR. Ester copolymers were enzymatically obtained from PCL and other poly(α,ω‐alkylene dicarboxylate)s and their microstructure depended on the polyester structure. 相似文献
2.
Summary: The microwave (MW)‐assisted lipase‐catalyzed ring‐opening polymerization of ε‐caprolactone in boiling solvents was investigated for the first time. In case of boiling toluene or benzene the MW‐assisted reaction proceeded significantly slower compared to oil bath heating. On the other hand, using boiling diethyl ether as solvent, an increase of the polymerization rate due to MW irradiation was found. Yield, molecular weight measurements, and MALDI‐TOF analysis supported the results.
3.
ε‐Caprolactone (CL) was enzymatically polymerized with 2‐mercaptoethanol as the initiator, both in an oil bath and under microwave (MW) irradiation. The polymerization performed under MW irradiation maintaining equal conditions led to higher yields and less formation of side products, i.e., a higher chemoselectivity was observed. The resulting polyester with a terminal SH moiety had a of 3 600 g · mol−1, determined by size exclusion chromatography (SEC), and was used as a chain transfer reagent. Subsequent copolymerization with styrene in different ratios led to polycaprolactone‐block‐polystyrene. SEC analysis and polarization microscopy of crystallized samples with different styrene contents proved the formation of block copolymers.
4.
The hyperfine interactions at 181Ta ions on Fe3+ sites in α-Fe2O3 (hematite) were studied in the temperature range 11–1100 K by means of the perturbed angular correlation (PAC) technique.
The 181Hf(β−)181Ta probe nuclei were introduced chemically into the sample during the preparation. The hyperfine interaction measurements
allow to observe the magnetic phase transition and to characterize the supertransferred hyperfine magnetic field Bhf and the electric field gradient (EFG) at the impurity sites. The angles between Bhf and the principal axes of the EFG were determined. The Morin transition was also observed. The results are compared with
those of similar experiments carried out using 111Cd probe.
aAlso at Comisión de Investigaciones Científicas de la Provincia de Buenos Aires, Argentina. 相似文献
5.
F. Renz D. Hill P. Kerep M. Klein R. Müller-Seipel F. Werner 《Hyperfine Interactions》2006,168(1-3):1051-1056
A series of pentadentate ligands N–X–5LH2 (X?=?H, Methyl, Benzyl)?=?N–X–saldptn (4-X-N,N′-bis(1-hydroxy-2-benzylidene)-1,7-diamino-4-azaheptane) has been prepared by a Schiff base condensation between 1,7-diamino-4-X-azaheptane and salicylaldehyde. Complexation with Fe(III) yields a series of high-spin (S?=?5/2) complexes of [FeIII(N–X–5L)Cl]. Such precursors were combined with [Mo(CN)8]4? and a series of blue nonanuclear cluster compounds [MoIV{(CN)FeIII(N–X–5L)}8]Cl4 resulted. Such star-shaped nonanuclear compounds are high-spin systems at room temperature. On cooling to 10 K some of the iron(III) centers switched to the low-spin state as proven by Mössbauer spectra, i.e. multiple electronic transitions. Parts of the compounds perform a high-spin to high-spin transition. Under light irradiation the populations are altered slightly. 相似文献
6.
The propylene-based 53,3-L?=?[N,N′-Bis(1-hydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] and ethylene-based pentadentate ligand 52,2-L?=?[N,N′-Bis(1-hydroxy-2-benzylidene)-1,5-diamino-3-azapentane] has been prepared. Complexation with Fe(III) yields high-spin (S?=?5/2) complexes of [FeIII(52,2-L)Cl] and [FeIII(53,3-L)Cl]. Such precursors were combined with [M(CN) x ] y? (M?=?W(IV), Mo(IV), Ru(II), Co(III)) and heptanuclear and nonanuclear clusters of [M{(CN-FeIII(52,2-L)} x ]Cl y and [M{(CN-FeIII(53,3-L)} x ]Cl y resulted. Such starshaped hepta- and nonanuclear compounds are high-spin systems at room temperature. On cooling to 20 K in all presented ethylene compounds the iron(III) centers switch to a second high-spin state as proven by Mössbauer spectra with a yield of about 30%, i.e., multiple electronic transitions. The propylene compounds, however, perform a high-spin to low-spin transition. Mössbauer spectra taken during green light irradiation indicate changes in the population of the different electronic states, i.e. concerted inorganic reaction. 相似文献
1