Poly(1,2-cyclohexylene carbonate) (PCHC) was prepared by copolymerization of carbon dioxide and cyclohexene oxide with Y(CCl(3)OO)(3)-ZnEt(2)-glycerin rare earth metal coordination ternary catalyst. The result polymer showed number average molecular weight (M(n)) of 56.3 x 10(3) with polydispersity index of 4.9. Though PCHC showed high glass transition temperature (T(g)), PCHC was easy to degrade during melt processing, accompanied by severe deterioration of its mechanical performance, which constituted one of the main obstacles for commercialization of PCHC. In order to impove the thermal stability and mechanical properties of PCHC, the thermal decomposition reaction was compensated by the chemical chain extension reaction. At first, maleic anhydride was used as end-capper of PCHC to prevent its chain unzipping reaction, the MA and PCHC in weight ratio of 1:100 were added into dichloromethane to make a 20 wt% solution,and refluxed at 41 similar to 43 degrees C for 48 h, then the polymer was precipitated by ethanol to obtain maleic anhydride end-capped PCHC (MA-PCHC). MA-PCHC was then subjected to chain extension reaction at 180 degrees C and 60 r/min in the a Haake mixer for 5 min using 2,2'-bis (2-oxazoline) (BOZ) as chain extender. The optimal chain extension condition was found when equimolar BOZ and carboxyl group in MA-PCHC were used, the M. of MA-PCHC increased from 5. 6 x 10(4) to 12. 4 x 10(4). The thermal stability of PCHC after chain extension was greatly improved,compared with the as-polymerized PCHC, the thermal decomposition temperature at 5 wt% loss (T(d-5%)) for chain extended PCHC increased from 260 C to 317 C, the Tg increased from 114 degrees C to 133 degrees C, and most importantly, the melt viscosity increased by 30 times. It should be noted that no significant change in gelatin content was observed during chain extension reaction. Moreover, the chain extended PCHC showed tensile strength increase from 35. 8 MPa (as polymerized PCHC) to 40. 2 MPa, and the elongation at break increased from 4. 59% to 6. 22%, yielding phenomenon was observed in the stress-strain curve. Therefore, the chain extension strategy was effective to improve the mechanical performance of PCHC.
The optical rotatory of helix polymer poly(triphenylmethyl methacrylate) (PTrMA) has been studied. The specific rotation of PTrMA is related with the length of helical chain linearly, while P(n)BAR<6 and P(n)BAR greater-than-or-equal-to 15. When P(n)BAR greater-than-or-equal-to 15, [alpha]D/20 = 1.6 P(n)BAR + 290-degrees. The contribution of each repeating unit to [alpha]D/20 is 1.6-degrees. In the 300-600 nm region, the ORD of PTrMA obeys both the Drude equation and Moffitt equation. The relationship between the [alpha]D of PTrMA and the solvent, concentration and temperature has also been investigated.
Spectra properties of Ce3+ ions and Eu2+ ions in KZnF3 were studied and energy transfer from Ce3+ to Eu2+ was observed in co-doped with Ce3+ and Eu2+ systems. Quantum yields of energy transfer were calculated, The investigated mechanism of energy transfer is electric dipole-dipole interactions, We also noticed that the existence of Ce3+ is conductive to observe f-f transition emission of Eu2+ ions.
OBJECTIVE To observe the effect of chronic lead contaminant on mRNA expression of protein kinase C (PKC) and calmodulin (CaM) in hippocampus of baby rats. METHODS The Wistar pregnant rats were randomly divided into 3 groups fed with distilled water and lead contained water (0.2% and 1.0% lead acetate) respectively. The lead exposure period was from the 0 day of pregnancy to the day when the offspring weaned. Then the baby rats were fed with lead water the same as their mothers. The cliff avoidance reflex within postnatal day 8 and step down test at postnatal day 50 were performed. Then pups were killed at postnatal day 8 and 50 respectively. Atomic absorption spectrometry was used to determine lead content of rats' brain. RT-PCR was used to observe mRNA expression of PKC and CaM in hippocampus of baby rats. RESULTS The brain lead content of test groups were much higher than that of the control group. The completion rate of cliff avoidance reflex and the score of step down test of test groups were lower than those in the control group (P < 0.05). Compared with control group, PKC and CaM mRNA expression of chronic lead exposure baby rats in the hippocampus had the down trend (P < 0.05). CONCLUSION The decrease of PKC and CaM mRNA expression level in hippocampus has a great link with the impairment of learning and memory induced by lead in baby rats, which might be one of the molecule mechanisms of lead induced impairment of learning and memory.
The mechanism and factors control- ling sex differentiation and sex deter- mination have long been a subject of interest but never fully explored.Experi- ments by Witschi and his co-workers (1914,1931,1933,1937,1957)in para- biosis,gonad transplantation,temperature control and hormone injections in amphi- bians have furnished many evidences showing that germ cells assumed the male or the female sex character not on the basis of their genie constitution,but was the result of the response to inductive stimuli received from embryonic sex inductors(cortex and medulla),and from the inductive substances(medullarin and corticin).Thus,the differentiation of male and female is determined by a quantitative relationship between the two inductive systems.The studies of Witschi and his associates have led them to the development of the inductive theory of sex differentia- tion which has found widespread accep- tance.In a recent report,Chang and Wi- tschi(1956)postulated that the cortico- medullary antagonism resemble an anti- gen-antibody mechanism;the primary in- ductors,corticin and medullarin,assum- ed the character of antigens and induced the production of antibodies,the corres- ponding anticorticin and antimedulla- tin,suppressing the contrary inductor system,are responsible for the unisexual development of each individual.But this hypothesis so far has not yet been demon- strafed by direct immunological method.
The slow voltammetry was taken on the paste electrode consisting of polyaniline powder and polytetrafluoroethylene binder which was applied to pyrographite disc electrode. The potential cycle range was+0.6V→-0.2V→+0.8V→+0.6V vs. SCE. It was found that the voltammetry curves are similar for polyaniline obtained chemically and electrochemically. The difference of the voltammetry curves in different acids may be attributed to some exchange of doping anions in polyaniline structure. The first redox ...
The preliminary work indicated that passive film is the most important factor influencing cell performance of carbon anode, and the carbon and solvent used govern cell performance by forming the passive film of different properties. A in situ XRD result is also presented.
The cleavage and formation of the di sulfide bond of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) were examined in an aqueous solution of pH value from 0 to 14 with and without polyaniline (PAn), The redox reaction of DMcT was accelerated by PAn in acidic condition. The cell using this anodic material was set-up and characterized in aqueous electrolyte.
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