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21.
Tanja Seraidaris Arto Puranen Mikko Karesoja Barbro Lfgren Timo Repo Markku Leskel Jukka Seppl 《Journal of polymer science. Part A, Polymer chemistry》2006,44(16):4743-4751
Elastic polypropene has gained growing industrial and academic interest as a thermoplastic elastomer. In this study, “rac”‐ and “meso”‐dimethylsilyl(3‐benzylindenyl)(2‐methylindenyl)hafnium dichloride complexes (Hfr and Hfm, respectively), activated with [NHMe2Ph][B(C6F5)4]/triisobutyl aluminum, were used in propene polymerization. Using these catalyst systems, we obtained polymers with high molar masses, up to 550 kg/mol, and moderate isotacticities between 34 and 52%. By varying the polymerization conditions, we could modify the polymer microstructure and molar mass. 13C NMR was used to calculate the polymer pentad sequence distributions. The crystalline parts of the polymers were analyzed with the differential scanning calorimetry successive self‐nucleation and annealing (SSA) technique. The SSA thermograms revealed that Hfr produced polypropene with a more uniform lamellar structure than Hfm. The mechanical properties were tested with dynamic mechanical analysis creep‐recovery tests. In the series, the polymers with the lowest isotacticities and therefore lowest crystallinities showed the best elastic properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4743–4751, 2006 相似文献
22.
Noora Ristolainen Ulla Vainio Santeri Paavola Mika Torkkeli Ritva Serimaa Jukka Seppl 《Journal of Polymer Science.Polymer Physics》2005,43(14):1892-1903
The properties of polypropylene composites can be tailored through the use of nanoclay fillers. The effectiveness of a metallocene‐catalyzed hydroxyl‐functional polypropylene in the compatibilization of polypropylene layered nanosilicate composites was studied, and the results were compared with those for a commercial maleic anhydride functionalized polypropylene. Polypropylene/organoclay nanocomposites were prepared by melt blending, and two polypropylene/compatibilizer/organoclay ratios, 90/5/5 and 70/20/10, were characterized. The organomodification of the clay was carried out with octadecylamine and N‐methylundecenylamine. The structure of the layered silicate was studied by transmission electron microscopy, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering. The fracture surfaces of the composites and thus the efficiency of the compatibilizers to penetrate the galleries of the organoclays were characterized by scanning electron microscopy, and the melt viscosity was studied by stress‐controlled rotational rheometry. The nanostructure was observed with both alkyl amines used for intercalation. The fillers facilitated the processability of all the composites, consisting of equal amounts of compatibilizer and organoclay filler and, in some of the composites, containing twice as much compatibilizer as organoclay filler. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1892–1903, 2005 相似文献
23.
We present a multifunction spectrophotometer for the measurement of light reflection from thick and transmission from very thin turbid liquid samples. Moreover, we present a method to get the complex refractive index of such turbid liquids. As an example of the high performance of the device and the method, we present data on inks that are used in offset printing. 相似文献
24.
25.
Excursion to the World of Heptacyclic Compounds Made of Azulenes and Acetylenedicarboxylates
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Yi Chen Erja Lehto Peter Uebelhart Anthony Linden Hans‐Jürgen Hansen 《Helvetica chimica acta》2015,98(7):913-937
Azulenes and acetylenedicarboxylates react under acid catalysis (Brønsted or Lewis) and form (2aRS,8aSR)‐2a,8a‐dihydrocyclopenta[cd]azulene‐1,2‐dicarboxylates as intermediate products, which then dimerize by central bond‐formation between C(2a1) and C(2′a1) and various peripheral C,C′‐atoms of the dihydroazulene fragments, depending on the substituents present. The reactions are often accompanied by the formation of side‐products, such as 2‐(azulen‐1‐yl)fumarates and ‐maleates and others caused by H‐shifts of the primary intermediates. H‐Shifts between the two tetrahydrocyclopenta[cd]azulene parts of the heptacyclic structures were also found. 相似文献
26.
Liu X Vesterinen AH Genzer J Seppälä JV Rojas OJ 《Langmuir : the ACS journal of surfaces and colloids》2011,27(16):9769-9780
We study the adsorption of a symmetric triblock copolymer of ethylene oxide, EO, and propylene oxide, PO, end-capped with quarternized poly(2-dimethylaminoethyl methacrylate), DMAEMA (DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24)). Light scattering and tensiometry are used to measure the relative size of the associated structures and surface excess at the air-liquid interface. The adsorbed amount, the amount of coupled water, and the viscoelasticity of the adsorbed polymer layer are measured on hydrophobic and hydrophilic surfaces (polypropylene, cellulose, and silica) by using quartz crystal microgravimetry (QCM) and surface plasmon resonance (SPR) at different ionic strengths and temperatures. The results of the experiments are compared with those obtained after adsorption of the uncharged precursor copolymer, without the cationic end-caps (EO(132)PO(50)EO(132)). DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) possesses higher affinity with the negatively charged silica and cellulose surfaces while the uncharged copolymer adsorbs to a larger extent on polypropylene surfaces. In this latter case, adsorption increases with increasing solution ionic strength and temperature. Adsorption of EO(132)PO(50)EO(132) on silica surfaces has little effect on the water contact angle (WCA), while adsorption of DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) increases the WCA of silica to 32°, indicating a large density of exposed PPO blocks upon adsorption. After adsorption of EO(132)PO(50)EO(132) and DMAEMA(24)-EO(132)PO(50)EO(132)-DMAEMA(24) on PP, the WCA is reduced by ≈14° and ≈28°, respectively, due to the exposed hydrophilic EO and highly water-soluble DMAEMA segments on the surfaces. The extent of surface coverage at saturation at the polypropylene/liquid interfaces (≈31 and 40 nm(2)/molecule obtained by QCM and SPR, respectively) is much lower, as expected, when compared with results obtained at the air/liquid interface, where a tighter packing is observed. The percentage of water coupled to the adsorbed cationic polymer decreases with solution ionic strength. Overall, these observations are ascribed to the effects of electrostatic screening, polymer hydrodynamic size, and solvency. 相似文献
27.
The boundary element spline collocation method is studied for the time-fractional diffusion equation in a bounded two-dimensional
domain. We represent the solution as the single layer potential which leads to a Volterra integral equation of the first kind.
We discretize the boundary integral equation with the spline collocation method on uniform meshes both in spatial and time
variables. In the stability analysis we utilize the Fourier analysis technique developed for anisotropic pseudodifferential
equations. We prove that the collocation solution is quasi-optimal under some stability condition for the mesh parameters.
We have to assume that the mesh parameter in time satisfies
(ht=c h\frac2a)(h_t=c h^{\frac{2}{\alpha}}), where (h) is the spatial mesh parameter. 相似文献
28.
This article deals with empty spacetime and the question of its physical reality. By “empty spacetime” we mean a collection of bare spacetime points, the remains of ridding spacetime of all matter and fields. We ask whether these geometric objects—themselves intrinsic to the concept of field—might be observable through some physical test. By taking quantum-mechanical notions into account, we challenge the negative conclusion drawn from the diffeomorphism invariance postulate of general relativity, and we propose new foundational ideas regarding the possible observation—as well as conceptual overthrow—of this geometric ether. 相似文献
29.
We show how some differential geometric ideas help to resolve some singularities of ordinary differential systems. Hence a
singular problem is replaced by a regular one, which facilitates further analysis of the system. The methods employed are
constructive and the regularized systems can also be used for numerical computations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
30.
Jukka Tanninen Samatha Platt Andreas Weis Marianne Nystrm 《Journal of membrane science》2004,240(1-2):11-18
The aim of the study was to test commercial and experimental NF membranes for their separation efficiency and acid resistance in a long-term filtration experiment. Several NF membranes (NF 270, Desal-5 DK, Desal KH, BPT-NF-1 and BPT-NF-2) were tested for their separation efficiency and stability when a solution containing 25 g/L CuSO4 and 8 wt.% H2SO4 was continuously filtered at 40 °C for 2 months. Filtration experiments were carried out with a new five-cell flat-sheet laboratory apparatus. Commercial NF membranes showed good selectivity, retaining most of the copper sulphate and letting most of the sulphuric acid pass into the permeate. However, only the membranes designed to be acid resistant (Desal KH and BPT-NF-2) maintained their separation efficiency during the 2 months of separation. The Desal KH membrane gave better copper retention values (92–95%) than the BPT-NF-2 (60–88%), but the overall selectivity was best with the BPT-NF-2 membrane due to its good sulphuric acid permeation. 相似文献