Search results for "Natta"

Synteza bimetalicznego silseskwioksanowego kompleksu tytanu(IV) i jego polimerycznego odpowiednika oraz ich właściwości katalityczne w polimeryzacji …

2016

Zsyntetyzowano, a następnie scharakteryzowano dwa tytanosilseskwioksany: nowy, nieznany dotąd z literatury, tetrachloroditytanosilseskwioksan (2) i jego polimeryczny odpowiednik (3). Zbadano właściwości katalityczne otrzymanych związków w polimeryzacji etylenu i 1-oktenu. Obydwa prekatalizatory, po aktywacji za pomocą Et2AlCl lub EtAlCl2, katalizują polimeryzację etylenu do polietylenu (PE) o małej masie molowej, która zmniejsza się zarówno ze wzrostem temperatury reakcji, jak i stosunku molowego Al:Ti. Kompleks (2) w połączeniu z metyloaluminoksanem lub związkami boru jest także aktywny w polimeryzacji 1-oktenu.

Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride immobilized on MgCl2‐based supports as a highly effective precursor for ethylene polymeri…

2009

Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride supported on MgCl2(THF)2 or on the same carrier modified by EtnAlCl3−n, where n = 1–3, was used in ethylene polymerization in the presence of MAO or a common alkylaluminium compounds as a cocatalyst. The support type alter vanadium loading and also change the characteristic of the catalytic active sites. Et2AlCl is the best activator for a catalyst which has been immobilized on a nonmodified support, whereas the systems which contain a carrier which has been modified by an organoaluminium compound reveal the highest activity in conjunction with MAO. That difference, together with different temperature effects on polymerization effi…

Dichlorovanadium (IV) complexes with salen‐type ligands for ethylene polymerization

2008

Vanadium complexes with tetradentate salen‐type ligands were first time explored in ethylene polymerizations. The effects of the vanadium complex structure, the alkyl aluminum cocatalysts type (EtAlCl2, Et2AlCl, Et3Al, and MAO), and the polymerization conditions (Al/V molar ratio, temperature) on polyethylene yield were explored. It was found that EtAlCl2 in conjunction with investigated vanadium complexes produced the most efficient catalytic systems. It was shown, moreover, that the structural changes of the tetradentate salen ligand (type of bridge which bond donor nitrogen atoms and type of substituent on aryl rings) affected activity of the catalytic system. The complexes containing li…

Synthesis and catalytic properties for olefin polymerization of new vanadium complexes containing silsesquioxane ligands with different denticity

2017

A series of new vanadium-silsesquioxanes (2a − 2d) was prepared by reacting VCl4 with not fully condensed silsesquioxanes (having from one to four silanol groups) and evaluated as pre-catalysts in olefin polymerization. The activation of 2a − 2d with EtAlCl2 generated highly active catalysts for ethylene polymerization, yielding high molar mass polymers with narrow dispersity. Ultra-high molar mass polyethylenes, Mw up to 4 × 106 g mol−1, were obtained with methylaluminoxane and Al(iBu)3/[Ph3C][B(C6F5)4] as activators. Upon treatment with methylaluminoxane and boron compounds, all vanadium pre-catalysts were active in 1-octene polymerization as well, and produced isotactic-rich poly(1-octen…

Organometallic VCl4-based catalyst supported on MgCl2(THF)2 for ethylene polymerization

1997

A Ziegler-Natta catalyst was obtained by milling VCl4 with the magnesium support in the from of the MgCl2(THF)2 complex, followed by activation with an organoaluminum compound. This catalyst was employed in low-pressure polymerization of ethylene. The system was found to offer a very high activity and to polymerize ethylene at a rate of a few hundred kg PE/(g Vh) with the resulting molecular weight of the product very high. The kinetic investgation of the polymerization process revealed over 80 % of the transition metal atoms to be involved in the forming catalytic active sites, undergoing virtually no deactivation over the period of time studied.

Strategic renewal : Can it be done profitably?

2022

Industry transformation requires strategic renewal at the level of individual firms. Executives then face the dilemma of choosing renewal paths in the face of uncertainty over the competitive environment of the future, and hence the profitability of potential strategies. This dilemma motivates us to study industry transformation from the perspective of strategic renewal among 208 large firms in the global pulp and paper industry. The findings of our qualitative comparative analysis show that only a minority of firms in our sample succeeded in profitable proactive renewal. Content-wise, there were similarities in the pursued strategies over the wider population, but only a few maintained sup…

Reaalioptiot investointien kannattavuuden arvioinnissa

2004

Jäähallien käyttötalous

2000

Firm growth and profitability : The role of age and size in shifts between growth–profitability configurations

2023

To investigate the routes toward profitable growth, this study partially replicates and extends the work of Davidsson et al. (2009) on firm growth–profitability dynamics with multi-industry data on over 66,000 Finnish firms. The results support prior findings on initial profitability being more important than initial growth for achieving high performance in both performance dimensions. Additional investigations on the role of firm age and size reveal further interesting dynamics: Very small young firms face fewer risks from growing at a low profitability level than other firms, and the benefits of firm size for future performance depend on the firm's current profitability. The results advan…

Ruokajärjestelmä uusiutuu – mutta miten?

2022

Maatalous ja ruoantuotanto ovat tärkeitä elinkeinoja maaseudulla, vaikka ruokajärjestelmän keskittyminen onkin kuorinut rahavirtoja maatiloilta kohti keskuksia. Fossiilitalouden mahdollistama suuruuden ekonomia on toiminut tämän keskittymiskehityksen tärkeimpänä moottorina. Samalla fossiilitalous yhdistettynä keskittymiskehitykseen on ajamassa suomalaisen ruokajärjestelmän kohti umpikujaa. Maataloussektorin pitäisi pystyä merkittävästi vähentämään kasvihuonekaasupäästöjä, vähentämään Itämereen ja sisävesiin päätyviä ravinnepäästöjä sekä torjumaan luontokatoa. Näitä kaikkia kehityskulkuja keskittynyt, fossiilitalouteen nojaava järjestelmä pikemminkin vahvistaa kuin lieventää. Järjestelmä ei …