Reactions Between AIRCl²and Ti (OR)₄and Activity in Diolefin Polymerization

Abstract

Through the use of a Ti(OR')4-AIRC12 catalyst system, high 1,4& isoprene polymers and crystalline 1,4-trans polybutadiene are obtained. Neither monomer is polymerized at a AI/Ti mole ratio of less than 4. The maximum activity and stereospecificity for isoprene is observed at AI/Ti = 4. For 1,4-trans butadiene polymers the activity increases progressively with increasing AI/Ti ratio. The investigations carried out on this catalyst system show that at a AI/Ti mole ratio of 4 the formation of crystalline P-TiClJ takes place, while at lower ratios insoluble chloroalkoxide derivatives of Till1 with different compositions separate. Soluble complexes containing aluminium and titanium are initially formed before precipitation occurs. Chemical data and investigations by IR and NMR spectroscopy indicate exchange reactions between Al-CI, AI-R, and Ti-OR groups, together with reduction of the transition metal. A reaction mechanism and a hypothesis on the nature of the active catalyst are given.

Highly trans‐1,4‐specific polymerization of 1,3‐butadiene catalyzed by [2,6‐bis{(4S)‐ (−)‐isopropyl‐2‐oxazolin‐2‐yl}pyridine] chromium complex activated with modified methylaluminoxane

“…The trans ‐1,4‐PBD obtained with 1 –MMAO is crystalline and shows two melting points at 78.2 °C (−Δ H m = 154.7 J g −1 ) and 135.7 °C (−Δ H m = 63.0 J g −1 ), while that obtained with 1 –MAO does not show a melting point in DSC measurements. Trans ‐1,4‐PBD is able to be synthesized with several catalyst systems containing transition metals such as lanthanoids,32, 33 titanium,34, 35 vanadium,36, 37 chromium,22 iron,23 cobalt38 and rhodium39, 40 (Table 3). The present 1 –MMAO system is one of the most trans ‐1,4‐specific catalysts for BD polymerization, although its activity is not very high.…”

Insight into the Synthesis Process of an Industrial Ziegler–Natta Catalyst

“…Although the reaction mixture turned yellow, no formation of any solid could be observed, thus confirming negligible precipitation of Ti-bearing species during the EADC addition. On the other hand, it was already demonstrated in the literature that Ti­(IV) complexes such as TiCl 4 can adsorb on sufficiently Lewis acidic crystal cuts of MgCl 2 , more specifically on the (110) face. ,− Thus, in Figure , the initial decay of Ti in the liquid phase with time can be explained by adsorption of chloro titanium alkoxides to the MgCl 2 crystallite faces. It follows that both Mg and Ti species contribute to the disappearance of Cl from the liquid phase during the initial stage.…”

“…The formation of soluble Ti(IV) complexes upon further addition of EADC can be explained by considering that alkoxychloro complexes of Ti(IV) can undergo complexation equilibria with EADC. 36 Through a molar balance of Cl and Ti getting soluble in this stage, the dissolution of Ti and Cl species occurs with a molar ratio of 1:2. This indicates that a complex with a possible formula of [TiCl 2 (OR) 2 ] has been released from the solid to the liquid phase.…”

“…Commonly, the Ti(IV) reduction occurs through transfer of an alkyl group to the Ti center and subsequent elimination of an alkyl radical, leading to the reduced form of Ti(III), Ti(OR) 3−x Cl x , which are insoluble in hydrocarbons. 36 In the study of Cucinella et al, it is concluded that under large excess of EADC, solid TiCl 3 is formed. According to our liquid-phase concentration measurements, the molar ratio of the precipitated Cl to the precipitated Ti during the heating step has a value of 3.75, which is in agreement with the study by Cucinella et al 36 Time Evolution of the ZNC Particle Size.…”

“…36 In the study of Cucinella et al, it is concluded that under large excess of EADC, solid TiCl 3 is formed. According to our liquid-phase concentration measurements, the molar ratio of the precipitated Cl to the precipitated Ti during the heating step has a value of 3.75, which is in agreement with the study by Cucinella et al 36 Time Evolution of the ZNC Particle Size. Particle Growth Mechanism.…”