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581.
Takanobu Aoyagi Takeo Araki Hisaya Tani 《Journal of polymer science. Part A, Polymer chemistry》1972,10(8):2325-2334
The catalytic behavior of binary systems derived from AIR3 and alkali metal hydroxide in a molar ratio of 1 to 0.5 in situ for stereospecific polymerization of acetaldehyde was studied for the purpose of preparation of isotactic polyacetal. The polymer obtained can be readily stretched to a film. The polymerization proceeds slowly (in ~20 hr). The polymer yield and stereospecificity of the polymerization by AlEt3–LiOH (1:0.5) catalyst were not significantly changed by the nature of solvent or dilution as far as studied. AlEt3–NaOH, AlEt3–KOH, AlEt3–CsOH, AliBu3–LiOH and AlMe3–LiOH in molar ratios of 1 to 0.5 behaved similarly. AlMe3–NaOH, AlMe3–KOH and AliBu3–NaOH also gave isotactic polymer of high stereoregularity but in lower yields. 相似文献
582.
Otsuki J Iwasaki K Nakano Y Itou M Araki Y Ito O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(14):3461-3466
Well‐defined supramolecular assemblies of Zn and free‐base porphyrins are constructed through the formation of amidinium–carboxylate salt bridges. A one‐to‐one donor–acceptor pair and a four‐to‐one antenna‐type assembly are investigated. The steady‐state and time‐resolved fluorescence measurements unequivocally showed that efficient singlet–singlet excited energy transfer from the Zn–porphyrin complex to the free‐base porphyrin takes place in these assemblies. Indeed, the observed energy‐transfer rates in both types of assemblies are much faster than those the Förster mechanism would suggest, implying the involvement of an intermolecular through‐bond mechanism. 相似文献
583.
Shigeo Tazuke Ryuichiro Takasaki 《Journal of polymer science. Part A, Polymer chemistry》1983,21(5):1529-1534
Three types of polymer electron transfer sensitizer were prepared by copolymerization of 1-pyrenylmethyl methacrylate with styrene (I), vinylbenzyltriethylammonium chloride (II), and sodium p-styrenesulfonate (III). Irradiation of the pyrenyl group in the presence of leuco crystal violet (LCV), in homogeneous or in heterogeneous systems, induced the formation of crystal violet cation (CV+) in air. The reactivity of I, II, and III was in the order of II > I > III in both systems; this was rationalized in terms of the Coulombic effect. The effect of charge is much greater for the heterogeneous systems. High-charge density on the polymer surface and enhanced polymer-solvent affinity account for the high reactivity of II. The high quantum efficiency, coupled with the advantage of facile product separation, warrants the practical application of interfacial sensitization. 相似文献
584.
The cis-doubly N-confused porphyrin, H2N2CP, containing two adjacent confused pyrrole rings has been investigated from the point of view of its acid-base and electrochemical behavior in dichloromethane. This novel porphyrin isomer can form two metal-carbon bonds in the central core, stabilizing metal ions in unusually high oxidation states. Furthermore, the two outside N-pyrrole atoms remain available for acid-base and specific solvent interactions. Protonation of the pyrrole N atoms proceeds according to two successive steps, while only a single deprotonation step has been observed in the presence of bases. Similarly, in the case of the silver and copper complexes the protonation and deprotonation of the outer pyrrole rings have been detected, confirming the structure of the metalated species as M(III)-HN2CP. The electrochemical reduction of the metal ions (III/II redox process) and oxidation of the macrocycle ring have been detected respectively at -0.9 and 1.4 V based on spectroelectrochemical measurements in conjunction with the acid/base equilibrium studies. Additional waves observed around -0.5 and 1.3 V have been assigned to redox processes involving water molecules associated with the doubly N-confused porphyrins. 相似文献
585.
Takeo Araki Koichi Nagata Hiroshi Tsukube 《Journal of polymer science. Part A, Polymer chemistry》1979,17(3):731-746
In the presence of Et2SO4, (S)-1-(N-phenyl-carbamoyl)-2-methylaziridine gave an oligomer with a structure of [CH2? CHCH3? N(CONHPh)]n. The oligomer has optically active isotactic configuration and narrow molecular weight distribution (DP ca. 8). The net polymerization behavior of the monomer and chemical property, such as absorptivity of Et2SO4, of the oligomer are analogous to the case of 1-(N-phenyl-carbamoyl)-aziridine. The ring opening occurs with retention of the configuration at the asymmetric carbon atom and the oligomer can be crystallized at around 90°C. 相似文献
586.
587.
The reaction between some aliphatic aldehydes (acetaldehyde, propionaldehyde and butyraldehyde) and the typical stereospecific polymerization catalyst R2AlOCR′NPh has been studied in an attempt to elucidate the initiation mechanism of the polymerization reaction. The monomer-catalyst (1/1) complexes obtained from these aldehydes and R2AlOCR′NPh possess excellent catalytic activity towards the stereospecific polymerization. The structure of the complex in solution has been determined by NMR and IR spectra and compared with the structure determined by X-ray structure analysis. The presence of pentacoordinate aluminum in the complex has been demonstrated, for the first time, by X-ray studies.The structure of the aromatic monoaldehyde complex has also been studied and shown to be identical with that of the aliphatic aldehyde complex mentioned above. The chemical behavior of these aldehyde complexes towards Lewis bases and Lewis acids has also been studied. The aldehyde moiety of the R2AlOCR′NPh - MeCHO complex is liberated by the action of a strong Lewis base such as trimethylamine oxide and hexamethylphosphoramide, and is easily exchanged for another kind of aldehyde. The trimethylaluminum complex, Me2AlOCPhNPh · MeCHO · AlMe3, which only leads to the formation of amorphous polyacetaldehyde in contrast to Me2AlOCPhNPh · MeCHO, has been isolated and its structure determined by IR, NMR and X-ray studies in order to establish the relationship between its structure and its chemical behavior. 相似文献
588.
A new stilbene, 4-[(2"E)-7"-hydroxy-3",7"-dimethyloct-2"-enyl]-2',3,4',5-tetrahydroxy-trans-stilbene (1), and the known compound chlorophorin (2) were isolated from the heartwood of Chlorophora excelsa. Both 1 and 2 showed tyrosinase inhibitory activity with IC(50) values of 96 and 1.3 microM, respectively. 相似文献
589.
A series of organoaluminum compounds [R2AlOCR′NPh]2, which are the reaction products between trialkylaluminum compounds and secondary acid amides and are excellent catalysts for stereospecific polymerizations of aldehydes, were isolated in the crystalline state. Chemical behavior of such compounds toward Lewis acids and bases were interpreted in terms of the structures of [Me2AlOCPhNPh]2 and its trimethylamine oxide complex Me3NO·AlMe2OCPhNPh which were determined by X-ray structure analyses. Reaction products of primary and tertiary acid amides with trialkylaluminum compounds were also studied. 相似文献
590.
G. Sugihara A. A. Nakamura T. -H. Nakashima Y. -I. Araki T. Okano M. Fujiwara 《Colloid and polymer science》1997,275(8):790-796
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, the differential
conductivity (∂κ/∂C)
T
,
P
vs. square root of concentration (√C) was employed in order to determine not only CMC but also the limiting molar conductance (Λ0) and the molar conductance of micellar species (ΛM).
Based on the data of the degree of counterion binding to micelles (β) determined previously at different temperatures ranging
15–50 °C at every 5 °C, the experimental values of the degree of dissociation (ionization) of a micelle (αEX) were calculated by regarding as αEX=1−β. The ratio ΛM/Λ0 corresponding to the ratio of slopes below and above CMC in the curve of specific conductivity (κ) vs. concentration (C), which has been often assumed to be the degree of ionization of micelles (α), was compared with the present αEX. However, the ratio ΛM/Λ0 (=α) was found to have a correlationship with αEX (=1−β) as αEX≈0.40×(ΛM/Λ0), or strictly, αEX=0.40 (ΛM/Λ0)+0.08, indicating that the simple ratio of the slopes below and above CMC in κ vs. C curve is not true for αEX=1−β. On the other hand, the method proposed by Evans gave a value closer to αEX compared with the simple ratio.
Received: 17 September 1996 Accepted: 8 April 1997 相似文献