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1.
Ethylene/propylene (E/P) and ethylene/1-octene (E/O) copolymers were polymerized with two bridged metallocene catalyst systems, Et(Ind)2ZrCl2/MAO and Et(Ind)2HfCl2/MAO, respectively. The copolymers produced and some commercial reference copolymers were characterized by DSC, SEC, DMA and 13C NMR. The Hf-catalysed E/P polymerizations showed much lower activities than the corresponding Zr-catalysed polymerizations but gave polymers with high molar mass. The Hf-based copolymers also showed two melting peaks which may be indicative of several active sites of the catalyst. A comparison of E/P copolymers, containing about 20 mol-% propylene and produced with Zr, Hf and homogeneous V-catalysts, respectively, indicated that the Hf and V-catalysts gave material more similar to each other. The E/O copolymers produced with Zr-catalysts gave very low molar masses and the reactivity ratios, calculated from the NMR data, indicated that the Hf-catalyst has a slightly higher reactivity for 1-octene and the Zr-catalyst some better reactivity for ethylene. Segregation fractionation studies by DSC indicated that a lower 1-octene feed gives more heterogeneous copolymers and the DMA measurements reveal the existence of a linear correlation between the 1-octene content and the intensity of the tan δmax peak. 相似文献
2.
Kshama Motha Ulla Hippi Kimmo Hakala Maija Peltonen Vuokko Ojanper Barbro Lfgren Jukka Seppl 《应用聚合物科学杂志》2004,94(3):1094-1100
This article reports a study of some functionalized polyolefins evaluated as compatibilizers in polyethylene nanocomposites. The functionalized polymers were prepared by direct metallocene‐mediated copolymerizations of ethylene and a functional comonomer. The prepared nanocomposites were evaluated for mechanical and barrier property enhancement. A good combination of mechanical and barrier properties was obtained with the metallocene‐based functionalized polyethylene. The toughness–stiffness balance was better than or comparable to that achieved with conventional functionalized polymers such as maleic anhydride grafted polyethylene. The results also indicated that these metallocene‐based functionalized polyolefins, when used as compatibilizers, could have relatively higher molar masses and lower functionality than those of conventional post‐reactor‐modified compatibilizers, and so the drawbacks associated with the latter could be avoided. Their inherent properties could also further improve the final nanocomposite properties. This was attributed to the more homogeneous nature of metallocene‐catalyzed polymers in comparison with post‐reactor‐modified products. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1094–1100, 2004 相似文献
3.
Transport of phosphorus forms and of nitrate through a clay soil under grass and cereal production 总被引:1,自引:0,他引:1
Many nutrients are lost from soil to water viatile drains. However, there are very few reliable studies of such phosphorus(P)losses under Swedish agriculture practices, especially in connection tofertiliser and slurry applications and related to nutrient balances. Tile drainlosses were measured from nine experimental plots in south-west Sweden; fourplots were measured for 7 years and five plots for 2–3 years. Cereals,mainly spring barley (Hordeum vulgare, L.) and oats(Avena sativa, L.), were grown in six plots, while oneplotwas cultivated with grass, timothy (Phleum pratense L.)andmeadow fescue (Festuca pratensis, L.), one with lucerne(Medicago sativa, L.) and meadow fescue (F.pratensis, L.), and the last one was a set-aside withgrass (Lolium perenne, L. and Trifoliumrepens, L.) that was neither fertilised nor used for crop removal.Attention was paid to the forms in which P was transported to water since thishas important ecological implications. Average losses of particulate P (PP)fromthe set-aside land was significantly lower than from the cerealproduction, but the average losses of soluble reactive P (SRP) and dissolvednonreactive P (DUP) were the same. Average loss of PP from the grass ley during 3years (0.09 kg per ha–1 y–1) wassignificantly less than the losses from cereal production. Total P loss of 0.3kg per ha–1 y–1 was equal to the averagelossfrom the Swedish monitoring network of observation fields. Compared to theaverage nitrate-nitrogen (NO3-N) leaching, which was 7 kg perha–1 y–1 from cereals, the NO3-Nleaching was very low from the plots with lucerne-grass and set-aside.After applying and directly ploughing in 80 kg ha–1 ofsuperphosphate for cereal production in November 1998, 0.6–1.8 kgSRP ha–1 y–1 was lost through the drain tiles.Surface application of cattle slurry in spring 1999 to the grass ley alsoresulted in a very pronounced increased base level of SRP. This paper documentsthe importance of applying slurry during dry conditions and of placingfertiliser into the soil according to crop requirements in the time perspectiveof one year. 相似文献
4.
Vinnars Bo; Thorm?hlen Barbro; Gallop Robert; Norén Kristina; Barber Jacques P. 《Canadian Metallurgical Quarterly》2009,46(3):362
Studies involving patients with personality disorders (PDs) have not focused on improvement of core aspects of the PD. The authors examined changes in quality of object relations, interpersonal problems, psychological mindedness, and personality traits in a sample of 156 patients with Diagnostic and Statistical Manual of Mental Disorders (4th ed.) PD diagnoses being randomized to either manualized or nonmanualized dynamic psychotherapy. Effect sizes adjusted for symptomatic change and reliable change indices were calculated. The authors found that both treatments were equally effective at reducing personality pathology. Only in neuroticism did the nonmanualized group do better during the follow-up period. The largest improvement was found in quality of object relations. For the remaining variables, only small and clinically insignificant magnitudes of change were found. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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6.
We are focusing on three alternative techniques-linear discriminant analysis, logit analysis and genetic algorithms-that can be used to empirically select predictors for neural networks in failure prediction. The selected techniques all have different assumptions about the relationships between the independent variables. Linear discriminant analysis is based on linear combination of independent variables, logit analysis uses the logistical cumulative function and genetic algorithms is a global search procedure based on the mechanics of natural selection and natural genetics. In an empirical test all three selection methods chose different bankruptcy prediction variables. The best prediction results were achieved when using genetic algorithms. 相似文献
7.
Total volatile organic compounds (TVOC) are determined in intake, room-supply and room air in 86 office rooms in 29 office buildings in northern Sweden. Measurements of formaldehyde were also made in room air. Building and room characteristics were identified and symptom reports collected from 1087 office workers. Concentrations of TVOC and formaldehyde in room air were low, with mean values of 71 µg/m3 and 31 µg/m3, respectively. The TVOC concentration was generally lower in room air than in supply air or intake air. The “loss” (difference in measured values) of TVOC from supply to room air was associated with raised concentrations of formaldehyde and raised prevalences of occupant symptoms. High TVOC concentrations in room air were associated with reduced prevalences of occupant symptoms. 相似文献
8.
Metallocene catalysts Et(Ind)2ZrCl2/MAO and Et(Ind)2HfCl2/MAO were used in ethene/propene copolymerization and in ethene/propene/5-ethylidene-2-norbornene (E/P/ENB) terpolymerization. The copolymerization activity of the Et(Ind)2ZrCl2/MAO system was 20 × 103 kgpolym/molMt *h, the Et(Ind)2HfCl2/MAO yielding 5 × 103 kgpolym/molMt *h. The polymerization activity decreased with diene addition, but this effect was significant only at very large diene feeds. The catalysts incorporated diene readily. Materials with an ethene content of 55 to 70 mol % and an ENB content of 2 to 16 mol % were produced. Et(Ind)2HfCl2 produced a considerably higher molar mass material than the Et(Ind)2ZrCl2 catalyst. The molar mass distributions were narrow. Copolymers and terpolymers with up to 3 mol % ENB content had some crystallinity. Copolymer Tgs were between −59°C and −55°C. The terpolymer glass transition temperature rose 1.5°C per wt % of ENB in the polymer. Polymer characteristics reported include composition, molar mass distribution, melt flow rate, density, and thermal behavior. The dynamic mechanical and rheological properties of the materials in comparison with commercial E/P/ENB terpolymers are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 35–44, 1997 相似文献
9.
Summary
Thirteen differently substituted long-chain amide- and amine-functional alkenes were synthesised and used as comonomers in
zirconocene/methylaluminoxane-catalysed copolymerizations with ethylene and propylene. Characterization of the prepared copolymers
showed the formation of functionalized copolymers with isolated comonomer units. The incorporation level of the comonomers
ranged from 0.24 to 1.3 mol % with ethylene and from 0.04 to 0.96 mol % with propylene. The molar masses of the copolymers
were lower than those of the corresponding homopolymers. End group analysis of the copolymers by NMR suggested that the dominant
chain termination mechanism was chain transfer to aluminium.
Received: 8 December 2000/Accepted: 12 February 2001 相似文献
10.
Environmental risk assessment of antibiotics in the Swedish environment with emphasis on sewage treatment plants 总被引:3,自引:0,他引:3
Lindberg RH Björklund K Rendahl P Johansson MI Tysklind M Andersson BA 《Water research》2007,41(3):613-619
The potential risks associated with antibiotics present in the Swedish environment were assessed using concentrations found in hospital effluent, and sewage treatment waters and sludge, in combination with data on their environmental effects obtained from the literature. For the aqueous environment, measured environmental concentrations and effect/no observed effect concentration ratios were much lower than one in most cases. The only exceptions, where concentrations of the investigated substances were high enough to pose potential risks, were the concentrations of the two fluoroquinolones, ofloxacin and ciprofloxacin, in the hospital effluent. Treating digested dewatered sludge by heat did not fully eliminate norfloxacin or ciprofloxacin, thus pellets may still contain high amounts of these substances (sub to low mgkg(-1)dw). In leaching tests less than 1% of the amounts of these fluoroquinolones in the sludge or pellets reached the aqueous phase, indicating that their mobility is limited if sludge is used to fertilize soil. 相似文献