Polymers containing hydrolytically labile trialkylsilyl ester side groups were synthesised via a conventional and a controlled radical polymerization. The trialkylsilyl methacrylate monomer unit was chosen for its capacity to hydrolyse into basic, acid or sea water varying the hydrophilic character of the resulting polymer backbone with time. The hydrolysis or saponification reaction of the ester bond of the trialkylsilyl methacrylate was monitored through a 1H NMR study showing the formation of siloxane side-products. Several copolymers and polymer blends were prepared as matrixes for controlled erodible systems. Their capacity to hydrolyse was demonstrated through SEM investigations with selective dissolution of free films containing hydrolysable copolymers and PMMA blends. Well-defined random and diblock copolymers with methyl methacrylate were investigated to show the effect of the microstructure on the erosion properties of the corresponding coatings. Poly(methyl methacrylate-b-tert-butyldimethylsilyl methacrylate) diblock copolymers synthesised through the RAFT process showed a better control of the erosion with a constant erosion rate over a long-time service in sea water at pH = 8.2. In addition, experiments showed that the erosion rate could be modulated by varying the molar proportion of hydrolysable side groups onto the copolymer backbone and the weight amount of copolymers mixed with PMMA in toluene solution. 相似文献
It was shown using eigenvalue analysis by Erdös et al. that with the exception of C4, there are no graphs of diameter 2, of maximum degree d and of order d2, that is, one less than the Moore bound. These graphs belong to a class of regular graphs of diameter 2, and having certain interesting structural properties, which will be proved in this paper. 相似文献
Ab initio calculations on the formation of carbonic acid from the hydration of carbon dioxide with water dimer are re-examined. Fully optimized geometries of the three stationary points (minima and transition state) with the 3-21G basis set are reported. They possess non-planar structures. The inclusion of polarization (with the 6-31G* basis) and electron correlation (via Møller-Plesset perturbation theory to second through to fourth-order using the 6-31G basis) tends to enlarge the energy barrier (35–40 kcal mol−1) for the double hydrogen transfer. This suggests that the neutral hydrolysis of CO2 could require more water molecules (an oligomer) in an autocatalytic process rather than a dimer. 相似文献
In this paper we study a system of linear operators between finite-dimensional Euclidean spaces. Emphasis is made on unbounded systems and sufficient conditions are established for their equi-surjectivity. An application is presented in which a system of approximate Jacobian matrices is used to obtain a parametric interior mapping theorem. A multiplier rule for vector problems is also derived. 相似文献
Two new coordination polymer frameworks Ni(NO2)2 (1) and Ni(4,4′-bipy)(NO2)2 (2) (4,4′-bipy = 4,4′-bipyridine) were synthesized by solvothermal reaction in formamide, and were characterized by elemental analysis, IR spectroscopy, single crystal X-ray diffraction, and magnetic measurement. In compound 1, each Ni2+ ion is linked with four neighboring Ni2+ ions through μ1,3-nitrito bridges forming 2D layered structure. In compound 2, each Ni2+ ion is bridged with six neighboring Ni2+ ions through four μ1,3-nitrito groups and two 4,4′-bipy ligands forming 3D structure. Magnetic measurements show weak ferromagnetism within framework of the two compounds with TN = 19 K (1) and 21 K (2). 相似文献
A procedure to exclusively obtain 3′S-cyanoanhydrovinblastine 12 from two naturally occurring vinca-alkaloids (catharanthine and vindoline) in one step with good yield is described. Stereoselective reductions of 12, providing straightforward access to three new vinca-alkaloids, including two diastereomers 3′S-cyano-(4′R,5′-dihydro)-anhydrovinblastine and 3′S-cyano-(4′S,5′-dihydro)-anhydrovinblastine as well as (3′S-aminomethyl)-(4′S,5′-dihydro)-anhydrovinblastine in good yields is also reported. 相似文献
This work presents the experimental study of the isomeric ratio of 137mCe–137gCe produced in 138Ce(γ, n) 137m,gCe photonuclear reaction, in neutron capture reaction 136Ce(n, γ) 137m,gCe and in the two simultaneous reactions 138Ce(γ, n) 137m,gCe and 136Ce(n, γ) 137m,gCe in the mixed photon—neutron field by the activation method. The investigated samples were irradiated at the bremsstrahlung photon flux, in the epithermal and thermal-epithermal neutron beam and in the mixed photon-neutron field constructed at the electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The results were analyzed, discussed and compared with those of other authors to examine the role of the channel effect in nuclear reaction and provide the nuclear data for theoretical model interpretation of nuclear reactions.