The structure of lower telomers produced by the sodium-initiated polymerization of butadiene in toluene, when the reaction of chain transfer to the solvent was pronounced, was studied by H-1 and C-13 NMR spectroscopy. It was shown that the terminal butadiene units of the telomers, which result from abstraction of a proton from the solvent, have an entire 1,4-structure in contrast to a predominantly 1,2-structure of the internal units. The experimental evidence indicates that the structure of the monomer units in the resulting polymer is not determined by the configuration of the growing chain end but depends on the transition state of the corresponding elementary act.
Kinetics of the bulk thermal radical polymerization of methyl acrylate initiated by phenylazotriphenylmethane was studied and variation of the molecular mass characteristics during the polymerization process was determined. It is established that the polymerization proceeds by a two-stage pseudoliving mechanism, with the number-average MM of the increasing linearly with conversion and the gel effect being completely suppressed. The possibility to perform a controlled bulk polymerization of methyl acrylate at high temperature is demonstrated.
The molecular mobility of poly(3-hydroxybutyrate) (PHB) was studied in the temperature interval from 20 to 90 degrees C by EPR using stable nitroxyl radicals 2,2,6 6-tetramethyl-1-peridinyloxy (Tempo) and 4-hydroxy-2.2,6,6-tetramethyl-1-piperidinyloxy (Tempol) as spin probes. Two series of PHB samples, prepared by different methods, possessed isotropic and textured morphologies. The noncrystalline phase of PHB contain regions of two types with markedly different molecular mobilities. It is suggested that "dense" regions, characterized by a comparatively low mobility of polymer chains, are located near the surface of crystalline grains, while the "loose" (amorphous) regions with a higher mobility of chains are more distant from the surface of grains. Molecular mobility in the dense regions was virtually the same for both isotropic and textured PHB samples, whereas the mobility in the loose regions was lower in the isotropic samples than in the textured ones. Saturation of the polymer with water vapor affected both the mobility of polymer chains and the relative content of loose and dense regions in the samples.
The effect of ferrocene on the kinetics of polymerization of methyl methacrylate was studied. It was shown that in the presence of ferrocene, the initial rate of polymerization initiated by benzoyl peroxide appreciably grows, and this phenomenon is accompanied by a significant reduction in the degree of polymerization of the resulting polymer. The orders of the polymerization reaction with respect to ferrocene and benzoyl per oxide and the activation energy of polymerization were determined. The parameters of the initiation reaction, namely, the orders of the reaction of initiation with respect to ferrocene and benzoyl peroxide, the energy of activation of initiation, the rate constant of initiation, and the pre-exponential factor, were calculated. It is inferred that ferrocene affects the parameters of the stage of initiation, while the characteristics of the reactions of chain growth and chain termination remain invariable.
Self-adhesive and adhesive contacts involving PS and poly(phenylene oxide) were studied at relatively low temperatures (below the glass transition temperature T-g) and short times (2 min), The lowest critical contact strength, for which adherence at the polymer interface still exists, is established to be 0.02 MPa. The energy required to break the polymer-polymer contact characterized by minimum strength is comparable to the reversible work of adhesion.
Experimental data concerning a specific mode of inelastic deformation of crystallizable polymers in the presence of liquid media, in other words, delocalized solvent crazing, are reviewed. The characteristic features of this mode of polymer deformation, are revealed, and its principal difference from classical solvent crazing is described. The data available on the mechanism of this phenomenon are analyzed.
The kinetics of the chemical etching of PET films irradiated by xenon ions with an energy of 1 MeV/nucleon was studied. It was shown that if the process of the film etching is preceded by annealing in air and aging in water, the kinetics of etching changes to an appreciable extent due to the occurrence of various adsorption, desorption, and diffusion processes in the latent tracks of ions in the polymer. As evidenced by the tritium label method, water which penetrates into the latent tracks exerts a plasticizing effect on the fractured polymeric material, favors its contraction, and provides incorporation of a part of volume occupied by the latent tracks into the etching zone along with the polymer surface.
In the ion-coordination polymerization of dienes catalyzed by lanthanide systems, the kinetic-activity distribution of active sites were determined using the molecular mass distribution curves obtained by the Tikhonov regularization method. The polymodal pattern of distributions suggests the presence of several yupes of active centers, which change their kinetic activity during polymerization.
A new monomer, 4,4'-bis(2,3,5-triphenylcyclopentadien-4-yl- l-on)tolane was synthesized by the reaction of 4,4'-bis(phenylglyoxalyl)tolane with a twofold molar amount of 1,3-diphenylacetone in ethanol. New acetylene-containing phenylated polyphenylenes were-obtained from this monomer and bis(acetylenes) by the Diels-Alder reaction in trichlorobenzene. Some properties of the resulting Polymers and the related films were studied, and it was demonstrated that the synthesized polymers can be crosslinked via triple bonds.
The samples of a triple Nylon-6-polyimide-Nylon-6 block copolymer containing 5 and 15% of polyimide (PI) were studied by DSC and X-ray diffraction in the WAXS and SAXS modes. Crystalline regions in the block copolymers studied comprise small Nylon-6-polyamide (PA) grains (predominantly in the a modification), which are subjected to rather insignificant influence of the rigid imide blocks squeezed out into the amorphous phase. The samples with 15% PI contain a small fraction of the crystalline Nylon-6 gamma* phase, which is related to hindered crystallization of the PA chains in the presence of PI. Analysis of the results of SAXS measurements shows that the structure of samples is most adequately described by a two-phase model with a crystalline phase of Nylon-6 and an amorphous phase comprising a mixture of PA and PI chains; Increased mechanical and thermal properties of the copolymers, as well as their high moisture resistance, can be explained using a concept of molecular composites comprising a flexible PA matrix reinforced by rigid PI fragments.
Variation of the microhardness of a PETP Film with the time of sample storage in a dry or humid atmosphere was studied and the effects of exposure to a constant magnetic field, plasma treatment, and plastic deformation under high pressure on this parameter were evaluated. The effects of external factors are most pronounced in the surface layers of polymer with a thickness not exceeding 10 mu m. The high-pressure treatment reduced the microhardness level. Exposure to the constant magnetic field led to acceleration of the relaxation processes in polymer samples upon the high-pressure treatment.
This paper summarizes advances in the field of polycondensation attained by the scientific school of academician Korshak: heterogeneous nonequilibrium matrix polycondensation in the presence of naturally occurring and synthetic polymeric matrices; equilibrium polycondensation in the presence of inorganic fillers which catalyze the process and lead to formation of filled polymers directly during the synthesis; polycondensation catalyzed by the rare-earth metal compounds; and polycondensation of nontraditional monomers.
Determination of the surface (two-dimensional) shear viscosity of a monolayer film by the method of slit viscometry in a Langmuir bath, developed for the study of structurized fluids possessing a yield point, is considered. Application of the method is illustrated by measurements of the surface viscosity of a mesomorphous cyclolinear poly(siloxane) film.
The blends of naturally occurring poly(saccharides), cellulose and chitosan, obtained in a solid phase under the combined action of high pressure and shear strain using various equipment were studied by electron microscopy, FT-IR spectroscopy, fractionation, potentiometric titration, X-ray diffraction, and elemental analysis. It was shown that a strong adhesion exists between chitosan and cellulose. According to the fractionational composition of the products, the produced: agglomerates are not stabilized by chemical bonds. As evidenced by IR spectroscopy, a system of hydrogen bonds formed between hydroxyl and amino groups of poly(saccharides) undergoes a qualitative change. This fact provides evidence that the blending of poly(saccharides) proceeds on a molecular level.
Features of the variation of structure and rheological properties of polymer blends in the vicinity of the point of phase separation are considered. The phase diagrams of polymer blends are characterized by the presence of an extended region of metastable states between the binodal and spinodal curves. This feature reflects a dual character of the polymer structure in these systems, with significantly different kinetic units-macromolecules and chain segments-involved in the liquid-liquid phase transition. The transient, incomplete character of the supermolecular structure of polymer blends at the phase separation point accounts for a sharp minimum of viscosity and the extremal character of variation of the other properties, as well as for a strong dependence of the phase transition temperature on the shear stress, molecular mass distribution, relaxation time, and some other factors.
The collapse mechanism for the Langmuir films cast from statistical and block copolymers and blends based on PDMS and PDES was studied. This study was aimed at determining whether the collapse involves random coil-helix or random coil-bilayer of linear PDMS transition. The experimental evidence made it possible to conclude that most likely collapse proceeds by the random coil-helix conformational mechanism.
The Kerr effect in nondeformed (isotropic) and predeformed polymer networks is theoretically studied within the framework of a model of three-chain network with Freely jointed chains between junctions. Also considered is the Kerr effect for macromolecules with a zero constant dipole moment. where the optically anisotropic chain segments are oriented in the external electric field due to the field-induced dipole moments. Dependence of the average difference [Delta a] = [a(parallel to) - a(perpendicular to)] of the chain segment polarizabilities in two principal directions (a(parallel to) and a(perpendicular to) along and across the field. respectively) on the field strength is calculated. The birefringence parameters of predeformed polymer networks exposed to strong electric fields can be used to evaluate the density of cross-links. The electrooptical parameters of the polymer films are compared to those of polymer solutions (melts). provided that the chain segments in both systems have identical chemical structures and equal molecular weights.
The radical copolymerization of a series of fluoro(meth)acrylates and methyl methacrylate carried our in the presence of a polyimide yielded new polymeric systems which surpass the corresponding homopoly(meth)acrylates prepared under analogous conditions with respect to their molecular mass characteristics, It was shown that the solubility and the thermal and mechanical properties of the resulting copolymers are appreciably different from poly(meth)acrylates even when the amount of polyimide introduced into the polymerization system is small.
The films deposited from plasma-activated vapors of the thermal decomposition products of poly(propylene) were studied by electron energy loss spectroscopy, X-ray photoelectron spectroscopy, electron diffraction, and electron microscopy techniques. The films with thicknesses exceeding 500 Angstrom are continuous and exhibit a quite smooth surface. The films structure represents a hydrocarbon matrix with a density of 1.1-1.3 g/cm(3) and disperse inclusions of higher density, probably, with a diamondlike structure. The content of inclusions does not exceed 10 wt %.
Effect of a low-frequency glow discharge on the structure of unisotactic PP films synthesized using a rac-EtInd(2)ZrCl(2)-methylalumoxane catalyst was studied. Exposure to the glow discharge plasma leads to changes in the hulk polymer structure, which depend on the relative content of gamma and alpha phases in the initial sample. An especially pronounced effect is observed in the samples containing less than or equal to 60% gamma-PP, where a nearly complete gamma --> alpha transition takes place. The transition is accompanied by increasing melting temperature (from 130 to 164 degrees C), growing molecular mass, and broadening molecular mass distribution; as a result, the properties of the initial unisotactic PP approaches those characteristic of the polymer obtained with conventional Ziegler-Natta catalysts. In addition, the structural transformations lead to an increase in the polymer crystallization rate and the Avrami parameter. When the gamma-PP content in the initial sample increases to 72%, only 10% of this phase transform into the alpha-PP. In samples with the gamma-PP content exceeding 80%, no structural transformations at all are observed upon exposure to the glow discharge plasma.
