A NMR Study on the Hydrolysis,Condensation and Epoxide Ring-Opening Reaction in Sols and Gels of the System Glycidoxypropyltrimethoxysilane-Water-Titaniumtetraethoxide

The examination of hydrolysis, homo- and hetero-condensation reactions, of the condensation degree and the extent of epoxide ring opening in the course of sol-gel process was carried out by means of liquid- and solid-state 29Si and 13C NMR in the system 3-glycidoxypropyltrimethoxysilane (GPTS)-titaniumtetraethoxide-water (molar ratio 1 : 1 : 1.5–14) which is frequently used for the synthesis of heterometal hybrid polymers. The monomeric silanol groups in the GPTS-prehydrolysate immediately co-condense with the Ti-tetraethoxide to Si–O–Ti bonds to an extent of about 50–60% which remain stable in sols and also in the corresponding gels at low amounts of free water (0.02 H2O/OR) in the sol. An increasing amount of free water in the sol (0.12 H2O/OR) leads to an increased hydrolytic cleavage of the heterometal bonds and to the formation of homo-condensed polysiloxanes. The condensation degree of RSiO1.5 units in the Ti-containing sols is with 30–60% relatively high in comparison to Ti-free GPTS sols (ca. 5%) whereas the condensation degree of GPTS derived gels (81%) was found to be similar to that of the Ti-containing gels (60–80%). Ti-tetraethoxide accelerates the ring opening reaction of the epoxide group in the sols in dependence on the water content. Up to 78% of the epoxide rings are opened after 24 h in the sol with the highest water content (2 H2O/OR). No epoxide rings can be detected in Ti-containing gels which derive from sols with an amount of free water of 0.12 H2O/OR. The results give a first insight into the different parallel reactions in this system and can contribute to more structure controlled syntheses of heterometal hybrid polymers.     

Darstellung und Eigenschaften löslicher und Polysiloxangebundener (Ether-Phosphan)ruthenium(II)-Komplexe

Preparation and Properties of Soluble and Polysiloxane-Supported (Ether-Phosphine)ruthenium(II) Complexes Phosphine-modified Polysiloxanes of the type x SiO₂ · [SiO_3/2(CH₂)₆P(Ph)R] (x = 0 – 3, I–IV ) were prepared by hydrolytic condensation of (MeO)₃Si(CH₂)₆P(Ph)R [ 1 ; R = CH₂CH₂OMe ( a ), CH₂C₄H₇O ( b ), CH₂C₄H₇O₂ ( c ), Ph ( d )]. Crosslinking was achieved by cocondensation of 1 and Si(OEt)₄. 2 SiO₂ · [SiO_3/2(CH₂)₆P(Ph)CH₂CH₂OMe] ( IIIa ) was investigated by means of ³¹P and ²⁹Si CP-MAS-NMR-spectroscopy, especially in view of a quantification of silyl species which revealed the following ratios: T₂:T₄:Q₂:Q₃:Q₄ = 76:158:48:135:82. Reaction of RuCl₂(PPh₃)₃ with 3 moles of 1a gave fluxional RuCl₂(P∩O)(P～O)₂ ( 4a ). From its temperature dependent ³¹P{¹H}-NMR spectrum the temperatures of coalescence and the corresponding activation enthalpies could be estimated at -25°C (46 kJ · mol^?1) and +20°C (55 kJ · mol^?1). Soluble 1a-d as well as their insoluble counterparts I-IV were treated with [RuCl₂(CO)₂]_n to give all-trans-RuCl₂(CO)₂(PR₃)₂ ( 6 ). On heating (120°C) 6 could be transformed into isomeric cis, cis, trans-RuCl₂(CO)₂(PR₃)₂ ( 7 ). Decarbonylation occurred on irradiation of 6 . Polysiloxane-supported ruthenium complexes were proved to be active in the heterogeneous hydrogenation of crotonaldehyde. Thus, at p(H₂) = 50 bat, T = 120°C, reaction time = 190 min, and at a molar ratio of aldehyde: Ru = 250:1, all-trans-RuCl₂(CO)₂(P～O)₂ ( 6f , O,P = IIIa ) effected a conversion of 50%, crotyl alcohol being formed in comparatively high selectivities. Moreover, no loss of metal or ligand from the support could be observed.     

Implementation of low temperature physical changes on silicone elastomers to achieve sensitivity gains through CPMAS NMR

Nuclear Magnetic Resonance Spectroscopy (NMR) has been used on several occasions to investigate the biodurability of silicone elastomers used in silicone breast implants. In all of these cases conclusions have been convoluted by lack of sensitivity. We have improved the sensitivity of solid state NMR characterizations of silicone elastomers used in silicone breast implants by changing the physical state of the elastomer. This was achieved by cooling the sample to −90 ^∘C, below its crystalline transition temperatures, and acquiring ²⁹Si Cross Polarization MAS (CPMAS) NMR. This approach yielded signal to noise enhancements as high as 8.5 fold for the elastomer backbone and modest improvements for (CH₃)₂RSiO_1/2 and silica filler signals.     

Caractérisation des feuilletages holomorphes singuliers, contenus dans des feuilletages Levi flat, sur les surfaces complexes compactes

Let be a holomorphic foliation with reduced singularities on a complex surface M and a real analytic codimension one foliation on M whose leaves contain the ones of . We show that a Levi flat group of diffeomorphisms of is resoluble and holomorphically conjugate to his normal form. We deduce, in one hand, that each singularity of  is conjugate to his normal form. In the other hand at each singularity m of , where is not defined, up a conjugacy, by the one form ω=xdy+ydx, one of the local invariant curves of , with non obvious holonomy, is contained in the set of singularities of . Moreover if M is a compact Stein variety we show, under some generic conditions, that has a 1-Liouvillian first integrating factor.     

Calculating formula and divisibility for relative class numbers of abelian function fields

In this paper abelian function fields are restricted to the subfields of cyclotomic function fields. For any abelian function field K/k with conductor an irreducible polynomial over a finite field of odd characteristic, we give a calculating formula of the relative divisor class number of K. And using the given calculating formula we obtain a criterion for checking whether or not the relative divisor class number is divisible by the characteristic of k.     

厅堂中总声压级的修正计算

完全扩散声场中的总声压级计算公式是假设混响声能在厅堂中的分布各处相等，与接收点的位置无关，实测发现该公式的计算值偏高，特别当接收点在临界距离以外时，本文提出了一个总声压级计算的修正公式，它与实测及计算机模拟的值符合较好。