B. Z. Volchek

ON THE MEMORY EFFECT IN UHMWPE NASCENT POWDERS

Morphology and molecular structure of three nascent ultra high molecular weight polyethylene (UHMWPE) powders synthesized on unsupported and supported Ziegler-Natta heterogeneous catalysts were studied with the help of electron microscopy and infrared (IR) spectroscopy. A synthesis was carried out in a slurry process in n-heptane at a temperature of about 70°C, which resulted in production of UHMWPE of one and the same molecular weight, approaching 106g/mol. The morphology of the nascent particles dramatically differed, however, which is evidence of the important role of the catalytic system used. Nascent particles synthesized on unsupported TiCl4 catalyst with EtAl as the cocatalyst had a globular structure, while those synthesized on supported TiCl4/Al2O3·SiO2 and TiCl3·0.3 AlCl3/MgCl2 Ziegler-Natta catalysts with the same cocatalyst demonstrated fibrillar (cobweb) and spiral (wormlike) structures, respectively. As revealed by IR spectroscopy, there was a significant difference in the nature of the crystalline regions formed during the synthesis/crystallization process; in the amount of short trans sequences not included in crystallites (taut tie molecules); in the content of irregular conformers of various types, including typical point defects 2G1 kinks; and so on. The melt-crystallized films produced from the investigated reactor powders were markedly distinguished by their drawability and by the existence and the amount of different molecular conformations despite a sufficiently high recrystallization temperature and prolonged preheating. The difference in molecular structure of the drawn films was retained in a whole range of draw ratios. It is concluded that there is a well-pronounced “memory effect” and the morphology of the original nascent particles depending on the catalyst/synthesis conditions clearly play a role in the properties of the end product. *Dedicated to Prof. Francisco J. Baltá Calleja on the occasion of his 65th birthday.

Optical constants of industrial polymers in the IR region

The optical constants have been measured by the techniques of IR transmission and ATR spectroscopy in the range 4000–400 cm−1 for four industrial polymers: polymethyl methacrylate, polystyrene, polyethylene, and polytetrafluorethylene.

Spectral emissivity of a Globar lamp in the 2-50-µm region

Computer modeling of the emissivity of a Globar lamp in the IR region has been carried out on the basis of a three-layer optical model. The metrological possibilities of calculating the high-temperature spectral emissivity of a composite multicomponent substance are estimated by the methods of classical dispersion analysis.

Synthesis and properties of polymeric and organo-inorganic amphiphilic sorbents molecularly imprinted with cholesterol

Polymeric and organo-inorganic sorbents molecularly imprinted with cholesterol were synthesized to create selective hemosorbents for efferent therapy of hypercholesterlemia. These sorbents are block copolymers of 2-hydroxyethyl methacrylate and ethylene glycol dimethacrylate and granulated organo-inorganic sorbents in which the imprinting was performed in the layer of the above copolymer on the surface of selenium (Se) nanoparticles stabilized with polyvinyl pyrrolidone. The physicochemical and sorption properties of the sorbents were studied.

Investigating the structural characteristics of monomeric layers of polymers by means of Fourier spectroscopy

This paper discusses the possibilities of using IR Fourier spectroscopy to investigate the orientational and conformational characteristics of single layers of polymers attached by one end to an impermeable surface (polymeric brushes). The method is used to determine the structural parameters of the polymeric branches of brushes attached to a cylindrical or flat surface.

Liquid Crystalline Ordering in Melts of Thermotropic Polymers with Malonic Acid Fragment in Spacer

Abstract With object to evaluate the effect of spacer chemical composition on chain conformation of thermotropic polymers in liquid crystalline (LC) state, linear and combined (main chain/side chain) polymers, containing fragment of malonic acid (FMA) in methylene spacer were studied. It is shown that owing to presence of FMA chain conformations of the studied polymers differ substantially from those of RF-polymers with simple methylene spacer. Tn 1c melt the main chain of polymers investigated has “hairpin”- like conformation with parallel allignment of neighbouring mesogens. In the case of combined polymers the side chain is located inside the hairpin, and mesogens of both main and side chains are round to be mutually parallel Described polymer structure in LC melt provides the explanation for experimentaily observed similarities between properties of LC melts of studied polymers and those of low molecular weight liquid crystalls.

Fourier transform infrared spectroscopic study of the kinetics of a first-order phase transition in tridecanoic acid CH3(CH2)11COOH

The structural changes in crystalline lamella cores of tridecanoic acid CH3(CH2)11COOH during heating in the range from the temperature T1 = 13.5°C to T2 > Tm = 41.6°C have been investigated using Fourier transform infrared spectroscopy. The behavior of the bands of rocking (in the region of 720 cm–1) and bending (in the region of 1470 cm–1) vibrations of CH2 groups in tridecanoic acid methylene segments has been analyzed. It has been shown that, in the first-order phase transition region (Ts–s ~ 36°C) within a narrow temperature range (ΔT1 ≤ 1 K), there is a gradual transformation of the initial triclinic subcell into the hexagonal subcell. The mechanism of this transition has been considered in terms of the theory of diffuse first-order phase transitions.

Pecularities of liquid crystalline order formation in polyesters with irregular chemical composition

Abstract Formation of liquid crystalline (LC) order in thermotropic main-chain random copolymers (containing mesogens of one type and spacers of different lengths) were investigated by IR spectroscopy, DSC, X-ray and polarized microscopy methods. It was demonstrated that in such copolymers (CPLs) smectic liquid crystalline (LC) order can exist. Peculiarities in spacers behavior during transition to LC state are found. Conclusion about the dependence of the mechanism of smectic LC order formation on chemical structure of rigid components of CPLs is made.