Isospecific Bulk Polymerization of Propylene with the Use of ansa-Metallocenes as a Mixture of rac and meso Isomers

The effects of various pathways of the formation of catalytic systems based on the rac-Me₂SiInd₂ZrCl₂ metallocene on the activity and properties of polypropylene prepared by the bulk polymerization of propylene were studied in detail. It was found that the conditions of formation of the catalytic system affect not only its activity and the character of kinetic curves but also the molecular weight of the synthesized polymer. Propylene polymerization was studied with the use of a number of bisindenyl derivatives of zirconium, which were mixtures of rac and meso forms that differ in the nature of substituents in the Si bridge or the indenyl ligand. The conclusion was drawn that, with the use of metallocenes as a mixture of rac and meso forms, high-molecular-weight isotactic polypropylene can be prepared with high stereoregularity at a very high rate; thereby, the stage of separation of a pure rac isomer can be excluded in the synthesis of the catalyst.     

Synthesis and chiral-optical properties of some benzolactams

Five- and seven-membered benzolactarns — (–)-S-2, 3-dimethyl-2, 3-dihydroisoindolone and (+)-S-5-methyl-2, 3, 4, 5-tetrahydrobenz[c]azepin-1-one — were synthesized. A study of their chiral-optical properties and comparison with the previously studied six-membered lactam (–)-S-4-methyl-3, 4-dihydroisoquinol-1-one showed that their circular dichroism spectra are similar: The spectra contain dichroic absorption bands due to ^* transitions in the aromatic chromophore (270 and 220 nm) and a band of charge transfer in the benzamide chromophore at 240–250 nm. The magnitude of the Cotton effect due to the charge-transfer band increases as the lactam ring becomes larger (five-membered < six-membered < sevenmembered benzolactam). The change in the magnitude of the Cotton effect is explained by the development of a strictly dissymetric chromophore.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 656–662, May, 1978.     

Composite materials based on fullerenes C60/C70 and polypropylene prepared via in situ polymerization

New composite materials based on isotactic PP and fullerene were prepared via in situ polymerization with the use of an isospecific metallocene catalytic system. The stress-strain properties, thermophysical characteristics, and reactivities of composites in reactions of high-temperature decomposition, oxidation, and chemiluminescence were studied. The appreciable effect of fullerene on the thermal oxidation and crystallization behavior of composites (an increase in the crystallization temperature by 10 K) was found. It was shown that the protective inhibitory effect of fullerene in PP oxidation reactions is due to the interaction of fullerene nanoparticles with peroxy macroradicals.     

A study of propylene polymerization over bimetallic titanium–vanadium catalysts

New bimetallic catalysts based on microspherical TiCl₃ modified with vanadium trichloride to obtain its different concentrations on the TiCl₃ surface were synthesized. The presence of a VCl₃ crystalline phase in the catalyst was confirmed by X-ray analysis. The synthesized catalysts were applied to studying propylene polymerization in a liquid monomer medium. The kinetics of the polymerization process was determined, and the structure and properties of the synthesized isotactic polypropylene (IPP) were established. It was demonstrated that the PPI samples synthesized over the developed titanium–vanadium catalysts has enhanced freeze resistance as compared to IPP sample obtained over conventional titanium catalysts.     

Syndiospecific polymerization of styrene in the presence of new titanium complexes with dialkanolamines: Titanocanes and bistitanocanes

The syndiospecific polymerization of styrene is studied in the presence of titanium complexes with dialkanolamines—bistitanocanes and titanocane—activated by individual MAO or the combined cocatalyst MAO/TIBA. It is shown that these catalysts are more active and stereospecific after their activation with the combined cocatalyst ([TIBA]: [MAO] ≤ 0.13) than that in the case of the activation with MAO: The activities of the catalysts are ≤18 and 9 kg PS/(mol Ti h), and the syndiotacticities of PS are ≤76 and 60%, respectively. Polymers synthesized in the presence of bistitanocanes are characterized by M _n ≤ 4.5 × 10⁴ and T _m ≤ 268°C and a narrow molecular-mass distribution (≤2.5).     

Raman Structural Study of Copolymers of Propylene with Ethylene and High Olefins

Nascent form of random copolymers of propylene with ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene was studied by Raman spectroscopy. The most significant spectral alterations with a change in propylene content were observed in two lines at 809 and 841 cm⁻¹. The first line corresponds to vibrations of polypropylene helical chains in the crystalline phase, while the second one is associated with vibrations of polypropylene helical chains having isomeric defects. Raman data confirm that conformational composition and phase state of copolymer macromolecules strongly depend on the comonomer content as well as on the size of the comonomer units.     

Towards DNA Nanomachines for Cancer Treatment: Achieving Selective and Efficient Cleavage of Folded RNA

Despite decades of effort, gene therapy (GT) has failed to deliver clinically significant anticancer treatment, owing in part to low selectivity, low efficiency, and poor accessibility of folded RNA targets. Herein, we propose to solve these common problems of GT agents by using a DNA nanotechnology approach. We designed a deoxyribozyme‐based DNA machine that can i) recognize the sequence of a cancer biomarker with high selectivity, ii) tightly bind a structured fragment of a housekeeping gene mRNA, and iii) cleave it with efficiency greater than that of a traditional DZ‐based cleaving agent. An important advantage of the DNA nanomachine over other gene therapy approaches (antisense, siRNA, and CRISPR/cas) is its ability to cleave a housekeeping gene mRNA after being activated by a cancer marker RNA, which can potentially increase the efficiency of anticancer gene therapy. The DNA machine could become a prototype platform for a new type of anticancer GT agent.     

High-Frequency Electron Transport under Pulsed Mechanical Action on Polypropylene–Graphene Nanoplates Composite

Doklady Physical Chemistry - A phenomenon of change in the frequency of a mechanically activated current was detected for the first time. This phenomenon consists in the fact that electric current...