Polymerization of .alpha.-Olefins and Butadiene and Catalytic Cyclotrimerization of 1-Alkynes by a New Class of Group IV Catalysts. Control of Molecular Weight and Polymer Microstructure via Ligand Tuning in Sterically Hindered Chelating Phenoxide Titanium and Zirconium Species

1995 ◽  
Vol 117 (11) ◽  
pp. 3008-3021 ◽  
Author(s):  
Arjan van der Linden ◽  
Colin J. Schaverien ◽  
Nico Meijboom ◽  
Christian Ganter ◽  
A. Guy Orpen
Keyword(s):  
Molecular Weight ◽  
Group Iv ◽  
Polymer Microstructure ◽  
New Class ◽  
Sterically Hindered ◽  
Alpha Olefins

Conjugates of Classical DNA/RNA Binder with Nucleobase: Chemical, Biochemical and Biomedical Applications

2019 ◽  
Vol 26 (30) ◽  
pp. 5609-5624
Author(s):  
Dijana Saftić ◽  
Željka Ban ◽  
Josipa Matić ◽  
Lidija-Marija Tumirv ◽  
Ivo Piantanida
Keyword(s):  
Molecular Weight ◽  
Small Molecules ◽  
Biomedical Applications ◽  
Protein Targets ◽  
New Class ◽  
Rna Targets ◽  
Covalently Linked ◽  
Structural Aspects

: Among the most intensively studied classes of small molecules (molecular weight < 650) in biomedical research are small molecules that non-covalently bind to DNA/RNA, and another intensively studied class is nucleobase derivatives. Both classes have been intensively elaborated in many books and reviews. However, conjugates consisting of DNA/RNA binder covalently linked to nucleobase are much less studied and have not been reviewed in the last two decades. Therefore, this review summarized reports on the design of classical DNA/RNA binder – nucleobase conjugates, as well as data about their interactions with various DNA or RNA targets, and even in some cases protein targets are involved. According to these data, the most important structural aspects of selective or even specific recognition between small molecule and target are proposed, and where possible related biochemical and biomedical aspects were discussed. The general conclusion is that this, rather new class of molecules showed an amazing set of recognition tools for numerous DNA or RNA targets in the last two decades, as well as few intriguing in vitro and in vivo selectivities. Several lead research lines show promising advancements toward either novel, highly selective markers or bioactive, potentially druggable molecules.

scholarly journals Multiplicity of Active-Site in Heterogeneous Ziegler-Natta Catalyst and Its Correlation with Polymer Microstructure

1970 ◽  
Vol 46 (4) ◽  
pp. 487-494
Author(s):  
ATM Kamrul Hasan
Keyword(s):  
Molecular Weight ◽  
Computer Simulation ◽  
Active Site ◽  
Photoelectron Spectroscopy ◽  
Active Sites ◽  
Chain Structure ◽  
Surface Complexes ◽  
Polymer Microstructure ◽  
Natta Catalyst ◽  
Ziegler Natta Catalyst

Multiplicity of active-site in heterogeneous Ziegler-Natta catalysts and its correlation with polymer microstructure was studied through the surface structure analysis of catalyst by computer simulation of X-ray Photoelectron Spectroscopy (XPS) data and microstructure investigation of polypropylene chains based on the deconvolution of the molecular weight distribution curves by multiple Flory most probable distributions using Gel Permeation Chromatography (GPC) method. The number and relative intensities of these peaks were found correlated to the distribution of multiple active sites. In this investigation, four individual categories of active sites were identified, each of which yields polypropylene with unique properties of molecular weight and chain structure different from other active sites. The reason of the multiplicity of active sites was determined by the presence of different locations of surface titanium species coordinated with other surface atoms or molecules. These different surface complexes of active species determine the multiple active site nature of catalyst which replicates the microtacticity, molecular weight and chain microstructure distribution of polymer. Keywords: Ziegler-Natta catalyst; Multiple active sites; Flory components; Computer simulation; Deconvolution; MWD. DOI: http://dx.doi.org/10.3329/bjsir.v46i4.9596 BJSIR 2011; 46(4): 487-494

Bimetallic Alkoxides of Nickel(II) with Niobium(V) and Tantalum(V)

1985 ◽  
Vol 40 (10) ◽  
pp. 1371-1376 ◽  
Author(s):  
R. Jain ◽  
A. K. Rai ◽  
R. C. Mehrotra
Keyword(s):  
Molecular Weight ◽  
Nickel Chloride ◽  
Reflectance Spectroscopy ◽  
Octahedral Geometry ◽  
Molar Ratio ◽  
New Class ◽  
Elemental Analyses ◽  
Visible Reflectance ◽  
Bimetallic Alkoxides ◽  
Interchange Reactions

A new class of bimetallic isopropoxides of nickel(II) with niobium and tantalum with the general formula, Ni[M(OPri)6]2, (where M = Nb or Ta) have been synthesized by the reaction of nickel chloride isopropanolate, NiCl2·ϰPriOH, with potassium hexaisopropoxy metalates, KM(OPri)6, (M = Nb or Ta) in the molar ratio 1:2. These derivatives have been characterized by elemental analyses, molecular weight determinations, infrared and visible reflectance spectroscopy in addition to magnetic susceptibility measurements. Alcohol interchange reactions of these bimetallic alkoxides have also been studied. On the basis of above studies, an octahedral geometry has been assigned to Ni(II) in primary bimetallic alkoxides while in secondary derivatives, it appears that there exists an equilibrium between octahedral and tetrahedral forms.

New Class of Reactive Polymer Modifiers for Asphalt: Mitigation of Moisture Damage

2000 ◽  
Vol 1728 (1) ◽  
pp. 52-59 ◽  
Author(s):  
Glen Crossley ◽  
Simon Hesp
Keyword(s):  
Molecular Weight ◽  
Tensile Strength ◽  
Asphalt Concrete ◽  
Lower Cost ◽  
Water Immersion ◽  
Polymerization Process ◽  
Reactive Polymer ◽  
New Class ◽  
Added Benefit ◽  
Polymer Modifiers

A new class of reactive polymer modifiers designed to improve binder-aggregate adhesion in asphalt concrete was evaluated. Using a controlled free radical polymerization process, polyisoprene was prepared with short blocks of reactive amino- or silane-functional monomer at one end of the polymer chain. The reactive polymers so synthesized were tested with a modified version of the Tunnicliff-Root method (ASTM D4867) for measuring retained tensile strengths after water immersion moisture conditioning at 60°C for 24 h. It was found that the retained tensile strength of the unmodified samples was 53 percent, and the retained tensile strength of the regular polyisoprene-modified control samples was between 57 and 69 percent, depending on the polymer molecular weight and content. The best retained tensile strengths of 86 and 90 percent, respectively, were obtained with samples modified with 3 and 5 percent by weight of the higher-molecular-weight silane-functional polyisoprene. The method for obtaining the desired effect is flexible; lower-cost monomers, such as butadiene, and more common polymerization methods, such as emulsion or anionic polymerization techniques, may be used equally well to produce polymers with similar or better performance characteristics. An added benefit is that the tested polymers imparted significant improvements in low-temperature performance measured with the thermal stress restrained cooling test.

Sign in / Sign up

Export Citation Format

Share Document