Molecular Weight Characteristics Of Polymers Research Articles

Neutral Red and Safranin Т in the Photopolymerization of Methyl Methacrylate and Other (Meth)Acrylate Monomers

Features of the polymerization of methyl methacrylate and a number of other (meth)acrylate monomers in the presence of catalytic systems based on phenazine dyes (Neutral Red and Safranin Т) under visible light irradiation are investigated. It is shown that amines of various structure as well as air oxygen affect the kinetic features of polymerization and the molecular weight characteristics of polymers. It is found that polymerization may proceed in the controlled mode up to high conversions at room temperature and a low photocatalyst concentration, among them without preliminary degassing of the reaction medium.

Effect of Solvent and Monomer Ratio on the Properties of Polyphenylene Sulphone.

For the first time, the effect of the solvent and monomer ratio on molecular weight, chemical structure, and mechanical, thermal, and rheological characteristics of polyphenylene sulfone has been studied. When dimethylsulfoxide (DMSO) is used as a solvent, cross-linking occurs during the processing of the polymer, which is accompanied by an increase in melt viscosity. This fact sets a pressing need for the complete removal of DMSO from the polymer. The best solvent used for the production of PPSU is N,N-dimethylacetamide. This study of the molecular weight characteristics of polymers by gel permeation chromatography showed the stability of the polymers practically does not change with a decrease in molecular weight. The synthesized polymers correspond in tensile modulus to the commercial analog Ultrason-P, while exceeding it in terms of tensile strength and relative elongation at break. Thus, the developed polymers are promising for spinning hollow fiber membranes with a thin selective layer.

Features of Methyl Methacrylate Polymerization Mediated by Methylene Blue and Ethyl 2-Bromoisobutyrate under Photoirradiation Conditions

Using methyl methacrylate polymerization as an example, the features of polymer synthesis in the presence of the catalytic system [methylene blue + ethyl 2-bromoisobutyrate] at room temperature under visible light irradiation are investigated. The effect of polymerization conditions, including the light irradiation wavelength and various structure activators, on the monomer conversion and molecular weight characteristics of polymers is estimated. It is shown that polymerization can proceed in the controlled mode under mild temperature conditions according to the atom transfer mechanism (Metal Free Atom Transfer Radical Polymerization) to high conversions at low photocatalyst concentrations.

Betulin‐containing bioactive amphiphilic copolymers: Synthesis, characterization and self‐assembly

AbstractBetulin, a natural triterpene possessing a wide range of biological activities, has been modified via Steglich esterification to produce a methacrylate derivative capable of participating in radical polymerization. The modification is intended to increase the solubility of betulin, which is almost insoluble in water, by incorporating into the composition of an amphiphilic copolymer. The resulting solubility of betulin in water increased from 8·10−5 mg/mL to more than 10 mg/mL per betulin. For this, well‐defined biocompatible thermoresponsive copolymers with high betulin content have been synthesized through the conventional and RAFT copolymerizations of betulin methacrylate (BeMA) with methoxy oligo(ethylene glycol) methacrylate (MOEGMA). BeMA was more reactive in the BeMA‐MOEGMA pair; the resulting copolymers were slightly enriched with BeMA units (r1 = 1.70, r2 = 0.93). The copolymers exhibited LCST‐type behavior. LCST was tuned by balancing the hydrophobic betulin and hydrophilic OEG fragments. The molecular weight characteristics of polymers and their behavior in aqueous and organic solutions have been studied. Copolymers obtained by conventional polymerization had lower cloud points than RAFT copolymers of the same composition. The copolymers are characterized by low critical micelle concentrations that decrease as the BeMA fraction in the copolymers increases. RAFT copolymers were shown to form unimolecular micelles resistant to dissociation, which is promising for their use in targeted drug delivery.

Polymerization of Hexene-1 and Propylene over Supported Titanium–Magnesium Catalyst: Comparative Data on the Polymerization Kinetics and Molecular Weight Characteristics of Polymers

Data are presented on the great differences of the kinetics of hexene-1 and propylene polymerization over the same supported titanium-magnesium catalyst, as well as molecular weight and molecular weight distribution of the polymers produced. It is found that the composition of cocatalysts (AlEt3 or Al(i-Bu)3 greatly affects the kinetics of hexene-1 polymerization and molecular weight distribution of polyhexene, contrary to data obtained at propylene polymerization. The presence of hydrogen at hexene-1 polymerization leads to a much higher increase of activity in comparison with propylene polymerization. Possible reasons for these differences are discussed on the basis of experimental results.

SYNTHESIS OF POLYMERS BASED ON STEARYL METHACRYLATE AND THEIR USE AS ADDITIVES FOR DIESEL FUEL

In this article the features of controlled radical polymerization of stearyl methacrylate in the presence of copper-based compounds in combination with nitrogen-containing ligands such as tris[2-(dimethylamino)ethyl]amine and tris[(2-pyridyl)methyl]amine were studied. The ethyl 2-bromoisobutyrate was used as the initiator of the polymerization process. The synthesized polymers were characterized by gel permeation chromatography and MALDI-TOF time-of-flight mass spectrometry. It was found that the proposed catalytic systems allow conducting controlled radical polymerization of stearyl methacrylate according to the Atom Transfer Radical Polymerization mechanism at relatively mild temperature conditions. It was revealed that the nature of the organic ligand has a significant effect on the rate of polymerization and the molecular-weight characteristics of the synthesized samples. Using the copper(I) bromide catalytic system in combination with tris[(2-pyridyl)methyl]amine as a ligand at reagents molar ratio of 1:4, the polymerization of stearyl methacrylate proceeded with high reaction rate to deep conversions in a wide range of molecular weights. The observed linear growth of the molecular weight of the polymer with increasing conversion and low polydispersity index of the synthesized polymers being at the level of 1.19-1.29, considered as an evidence of the controlled mode of polymerization. The influence of the molecular weight characteristics of polymers based on stearyl methacrylate on the low-temperature properties of diesel fuel of specification24-2000 produced by OOO «LUKOIL-Nizhegorodnefteorgsintez» was evaluated using a low-temperature analyzer MX-700 (PE-7200I) in accordance with the requirements of Russian (GOST 5066-91 and GOST 20287-91) and the international (ISO-3016) standards for the quality of petroleum products. It was established that the synthesized polymers can be used as additives that reduce the temperature range of solidification of environmentally clean diesel fuels, while the molecular weight of polystearyl methacrylate has a significant effect on the depressor properties of the fuel.Forcitation:Simanskaya K.Yu., Grishin I.D., Grishin D.F. Synthesis of polymers based on stearyl methacrylate and their use as additives for diesel fuel. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 82-89

Isobutylalumoxanes as high-performance activators of rac-Et(2-MeInd)2ZrMe2 in copolymerization of ethylene with propylene and ternary copolymerization of ethylene, propylene, and 5-ethylidene-2-norbornene

Isobutylalumoxanes have been obtained by hydrolysis of triisobutylaluminium (TIBA) with water in the form of vapour (1) or ice particles (2) at AlTIBA/H2O = 2 mol/mol. 1H NMR spectra of hydrolyzates showed the presence of unreacted TIBA indicating the formation of alumoxanes larger than i Bu2Al-O-Al i Bu2 which one can expect based on the molar ratio of reagents. Alumoxanes 1 and 2 demonstrate high activating ability for rac-Et(2-MeInd)2ZrMe2 in copolymerization reactions of ethylene with propylene and terpolymerization of ethylene with propylene and 5-ethylidene-2-norbornene. Alumoxane 1 demonstrates high structural and chemical stability during long-term storage (for 1 year) that results in consistent activating ability and similarity of molecular weight characteristics of polymer formed. Alumoxane 2 is much less structurally stable which is manifested in considerable changes of 1H NMR spectra of the product even after several days of storage. It essentially loses activating ability after 3 months’ storage. The alumoxanes with high activating ability have been also obtained by in situ TIBA hydrolysis with water intentionally incorporated into toluene (~1 × 10−2 mol/l) prior to polymerization also at AlTIBA/H2O = 2 mol/mol. The differences of catalytic systems with different activators are also reflected in differences in microstructure, molecular-weight, thermal-physical characteristics and physical-mechanical properties of copolymers formed.

Bis(3,6-di-tert-butylcatecholato)tin(IV) ditetrahydrofuranate in radical polymerization of methyl methacrylate

The effect of bis(3,6-di-tert-butylcatecholato)tin(IV) ditetrahydrofuranate (1) on the kinetic parameters of methyl methacrylate polymerization and on the molecular weight characteristics of polymers prepared was studied. According to EPR data, complex 1 can accept and eliminate the growing macroradicals in monomer media. This allows the lifetimes of the growing polymer chains to be controlled. The optimal temperature range for accomplishing controlled synthesis of polymer in the presence of complex 1 was determined.

Homogeneous and supported catalysts based on bis(imino)pyridyl Iron(II) complexes for ethylene polymerization

Data on ethylene polymerization on homogeneous and supported catalysts based on 2,6-bis(imino)pyridyl Fe(II) complexes activated by trialkylaluminums are considered (activity, the molecular-weight characteristics of polymers, the number of active sites, and the propagation rate constants). Unlike homogeneous systems, the supported catalysts prepared with the use of various carriers (SiO2, Al2O3, and MgCl2) exhibited high stability and activity at 70–80°C and produced high-molecular-weight polyethylene with a broad molecular-weight distribution (MWD). The molecular weights and MWDs of polymers and the propagation rate constant depended on the nature of the carrier only slightly. The reasons for an unusual effect of an increase in the activity of the supported catalysts in ethylene polymerization in the presence of hydrogen are discussed.

Mathematical Modeling of Continuous Butadiene Polymerization

Butadiene polymerization on a cobalt-containing catalyst in a continuous reactor is modeled. Expressions for the molecular-weight characteristics of polymers are derived. The contributions from chain transfer and polyaddition reactions to the breadth of the molecular-weight distribution of the polymer are analyzed.

Polymerizable siloxane precursors having in‐chain perfluoroalkyl groups

AbstractThe synthesis and polymerization of several silphenylene siloxane polymer precursors containing a perfluoroalkylsegment in the backbone was carried out. The molecular weight characteristics of polymers from 1,3‐bis[p(‐hydroxydimethylsilyl)phenyl]hexafluoropropane and 1,3‐bis[p(‐dimethylaminodimethylsilyl)phenyl]hexafluoropropane were studied as a function of polymerization conditions. Polymers containing the dodecafluorohexane chain segment were also prepared. Polymers having inherent viscosities of 0.55 to 0.9 were obtained. The polymers crosslinked at room temperature to thermoset elastomers which were characterized by improved thermal and oxidative stability over dimethylsilicones. Room temperature swelling of the experimental polymers hydrocarbon solvents was also much lower than that of dimethylsilicones. The polymers containing the (CF2)3 and (CF2)6 linkages had glass transition points of −12°C and −34°C, respectively.

Effect of the conditions of polycondensation on the branching characteristics of polyarylates

It is well known that the properties of linear and branched macromolecules of the same chemical composition and molecular weight can differ considerably. These differences can become apparent during use of the materials. Therefore study of the properties of polymers with differenct types and degrees of branching is of practical value. There are various causes of branching of marcromolecules, such as thermal and thermal-oxidative processes, occurring during both formation and use of plastic articles and during synthesis of the polymer, in high-temperature polycondensation for example, the presence of impurities etc. However the changes in the molecular-weight characteristics of polymers that accompany formation of branched macromolecules evidently obey general laws.