Summary:In the frequency range below $150 cm À1 , the longitudinal acoustic modes (LAM) localized along straight chain segments (SCS) of macromolecules emerge in the Raman spectra of linear semicrystalline polymers. The LAM frequency is inversely proportional to the SCS length; therefore, the LAM band contour reflects the SCS length distribution in a sample. The opportunities given one by the low-frequency Raman spectroscopy for studying the ordered structures in polyethylene are demonstrated and discussed. The illustrating material consists of both previously published and original data on nucleation and transformation of the ensemble of SCS in powder-like, gelled, and drawn ultra-high molecular weight polyethylene.
High-molecular-weight copolyesters based on ethylene glycol, tetraphthalic and 4,4′-biphenyl dicarboxylic acids containing up to 10.3 mole % of a second component were synthesized in the presence of homo-and heterogeneous catalysts. It was found that synthesis of these copolymers with a heterogeneous catalyst yields polymers with a higher molecular weight. The thermochemical properties of the copolyesters obtained were investigated. The thermostabilizing effect on addition of up to 10.3 mole % ethylene-4,4′-biphenyl dicarboxylic acid units to the PET polymer substrate was demonstrated. It was hypothesized that this modifier is a mesogen with respect to poly(ethylene terephthalate).The major possibility of obtaining high-strength, high-modulus industrial fibres from thermotropic polyesters was established more than half a century ago [1]. However, intensive research in this area is continuing to this day, due to the importance of creating new, effective types of reinforcing materials.The basic problem whose solution will determine the possibility of practically implementing these technologies consists of developing methods of synthesizing fibre-forming copolyesters containing mesogenic units. Such polymers must pass into the viscous-flow state with formation of temperature and time stable melts and be characterized by lower (in comparison to the corresponding homopolyesters) mechanical glass transition temperatures (t mg ).p-Hydroxybenzoic, 2-hydroxy-6-naphthoic, and 2,6-naphthalene dicarboxylic acids were used as the mesogen for obtaining thermotropic homo-and copolyesters, and derivatives of hydroquinone, 2,6-dihydroxynaphthalene, and other products were used as diols [2]. High-temperature equilibrium polycondensation of aromatic dicarboxylic acids and diols, hydroxycarboxylic acids, etc., in inert medium at 300-350°C is the basic method of obtaining fibre-forming thermotropic polyesters [3].Incorporation of mesogenic units in the poly(ethylene terephthalate) (PET) macromolecule gives melts of fibre-forming polymers thermotropic properties and causes the appearance of a mesophase in the spun fibre, which makes it possible to attain high orientation draw ratios and consequently to increase the initial modulus, strength, and fatigue characteristics of the fibre. A similar processing effect can be attained in spinning fibres from melts of a mixture of PET/poly(ethylene-2,6-naphthalate)/poly(p-hydroxybenzoate) in the ratio of 22.5/67.5/10.0 [4].The information on the possibility of using dihydroxy-and dicarboxyl-containing biphenyls as mesogens is episodic in nature. Moreover, the use of these compounds as PET modifiers is of great interest for production of high-strength, highmodulus, industrial polyester fibres. As a result of the studies in [5, 6], a method of obtaining 4,4-biphenyl dicarboxylic acid (BPDA) from by-products of synthesis of terephthalic acid dimethyl ester (DMT) was proposed. We investigated the effect of catalysts of polycondensation based on antimony -Sb(III) -compounds on the physicochemical pr...
543.544.45.38 T. I. Samsonova, and A. V. Genis Studies were conducted on separation of organic substances with different boiling points and polarity when simultaneously present in water by capillary gas-liquid chromatography on a Kristall 2000 m chromatograph.The effect of the column phase and temperature conditions on the separation factor and component exit time was investigated. Column temperature programming was used to reduce the component, especially heavy component, retention time. The chromatography regime was selected and a fast method was developed for determining components with different volatility in water during one analysis with suffi ciently high reproducibility and reliability of the results. It was shown that the time of the analysis decreased by more than two times with the same accuracy as with the standard methods. The method can be recommended for fast analysis of wastewaters for making a decision on the treatment method.Capillary gas-liquid chromatography is an effi cient method of determining low concentrations of organic substances. In this method, columns (capillaries) are used without any special carrier with the stationary phase applied on the inside of the capillary. This type of column ensures more effi cient separation in almost all cases than packed columns and columns with porous sorbents and allows conducting a quantitative analysis in lower concentration ranges. As a result of the studies using capillary gas chromatography, methods were developed for determining contaminants in monomers and solvents and many other organic compounds in waste and natural water [1-4]. These methods include chromatographic conditions (columns, temperature) that allow determining organic substances with different boiling points separately or groups of substances with close boiling points and polarity. At the same time, the process media of the enterprises, including the wastewaters, can contain organic contaminants that strongly differ in boiling point. In this case, several methods are used, and since the conditions of determination usually differ, the equipment must be realigned and calibrated or different chromatographs must be used. This increases the duration and cost of the analysis. For quickly obtaining information on the composition of production media, fast methods that allow obtaining the necessary information after one analysis are required. The instrument base for realization of the chromatographic method now allows expanding its possibilities, including programming of the column temperature.We will examine the possibility of using capillary gas-liquid chromatography and the new generation of gas chromatographs for simultaneously determining the content of compounds with different boiling points in water to analyze the process media of chemical fi bre plants. It ensures good separation of contaminants and suffi ciently high reproducibility, and reliability of the results.Scientifi c-Research Institute of Synthetic Fibres with Experimental Factory, Tver'.
The crystalline phase of gelled ultrahigh molecular weight polyethylene derived from reactor powders with different synthetic prehistories is studied by means of low frequency Raman spectroscopy and small angle X ray scattering. The results obtained suggest that the gels contain folded crystallites 3-6 nm in size that, in some samples, form stacks of two or more units bound by common straightened segments of mac romolecules (double folds). The gels are used to prepare highly oriented polyfilament fibers, and the strengths and Young moduli of the fibers are estimated. The gels containing stacks of crystallites demonstrate better ability to form high strength fibers during hot drawing than the gels containing individual crystallites. The effect of the strength of junctions in the polymer spatial network of the gels on the attainment of optimum mechanical properties of the drawn fibers is discussed.
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