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SynopsisThe kinetics of ethylene polymerization with TiCl,/MgCl,/SiO, has been investigated in the range of temperatures between 40 and 90°C and in the range of ethylene pressures between 4 and 12.4 kg/cm2. The role of MgCI, was discussed from the dependence of the Mg/Ti ratio on the catalytic activity. The polymerzation rate was first order with respect to the monomer concentration and the dependence of the polymerization rate on the concentration of Al(C,H& could be described by the Langmuir-Hinshelwood mechanism. The dependence of initial rate and the time to reach the maximum polymerization rate on the concentration of Al(C,H,), was also discussed. Polymerization rates as a function of the polymerization temperature showed a maximum and the activation energy was 11.8 kcal/mol between 50 and 80°C. The polymerization rate decreased with the increase of hydrogen partial pressure. The active site concentration ( C * ) was 1.9 X mol/mol Ti by the inhibition method with carbon monoxide.

Realizing a state of matter in two dimensions has repeatedly proven a novel route of discovering new physical phenomena. Van der Waals (vdW) materials have been at the center of these now extensive research activities. They offer a natural way of producing a monolayer of matter simply by mechanical exfoliation. This work demonstrates that the possible multiferroic state with coexisting antiferromagnetic and ferroelectric orders possibly persists down to the bilayer flake of NiI2. By exploiting the optical second-harmonic generation technique, both magnitude and direction of the ferroelectric order, arising from the cycloidal spin order, are successfully traced. The possible multiferroic state's transition temperature decreases from 58 K for the bulk to about 20 K for the bilayer. Our observation will spur extensive efforts to demonstrate multi-functionality in vdW materials, which have been tried mostly by using heterostructures of singly ferroic ones until now.

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