Showing papers in "Polymer Science U.s.s.r. in 1983"

Conformations of polymer chains grafted to an impermeable plane surface

Abstract: A scaling method has been used to investigate a system of long polymer chains grafted at one end to an impermeable plane surface. The thermodynamic rigidity of the graft chains and the solvent quality are taken into account. A diagram of state has been constructed and the equilibrium characteristics determined for the system in each of the regions identified in the diagram. The influence of rigidity of the macromolecules on the shape of the diagram of state is discussed.

Molecular structure and physical properties of rigid chain polymers in solutions. Review

Abstract: The results of experimental investigations of the physical properties of the molecules of rigid chain polymers are generalized using the methods of translational friction and viscosity and dynamic and electric birefringence in solutions. The main results of the theories of hydrodynamic properties and optical anisotropy of chain molecules are discussed and also the dynamo-optical and electro-optical effects in steady and dynamic regimes. The conformational, hydrodynamic, optical and dipole characteristics of the rigid chain molecules obtained with use of the above methods are compared with the corresponding properties of flexible chain molecules.

Role of end groups in polyvinylidene fluoride

Abstract: A study has been made of PVDF samples prepared in the presence of various initiators. It was found that nature of PVDF end groups determines the degradation mechanism of the polymer, and influences its thermal stability, fire resistance, and dielectrical and rheological properties.

Use of modulation of elliptic light polarization for the study of electric birefringence of polymer solutions in pulse fields

Abstract: A compensation method was developed for measuring electric birefringence in the pulse field of constant and sinusoidal voltage which is based on the use of modulation of elliptic light polarization. The method enables the equilibrium Kerr effect and kinetics of electric birefringence of conductive polymer solutions to be examined.

Viscometric properties of dilute solutions of hydrolyzed polyacrylamide

Abstract: The authors have measured the concentration dependence of the reduced viscosity ηsp/c of hydrolyzed polyacrylamide with different degrees of hydrolysis h and neutralization α in dilute solutions of different ionic strength Cs. It is shown that [η] of the polymer (α=1) is a linear function of 1/√Cs. At Cs = 1·91 mole/l. the value [η] does not depend on h so that the MW of hydrolyzed polyacrylamide with different h may be calculated from the same Mark-Kuhn formula. For samples with h ⩾0·2 and α⩽0·5 an anomalous dependence of function ηsp/c-c is found for all values of Cs studied (0·005−1·910 mole/l.) which is explained by the self-ionization of the neutralized carboxyl groups of the polymer on dilution of the solution and the associated increase in the charge of the chain molecule and also by rupture of the possible intramolecular hydrogen bonds between the amide and carboxyl groups.

Relations between the thermal stability of partially fluorinated polymers and their structure

Abstract: The thermal stability of polyvinylidene fluoride and the copolymer of tetrafluoro-ethylene with ethylene of equimolar composition has been investigated. Polyvinylidene fluoride degrades by dehydrofluorination and depolymerization, while degradation of the copolymer is preferentially in accordance with a depolymerization mechanism. The apparent activation energies of dehydrofluorination have been calculated, and features of this process are discussed in relation to the mode of alternation of methylene and perfluoromethylene groups in the chain.

Characteristics of binding of metal ions with polymeric ligands

Abstract: The process of binding and distribution of metal ions between polyligand molecules has been analysed for the systems: poly-4-vinylpyridine-Cu 2+ , Ni 2+ , H + , quaternized poly-4-vinylpyridine-Cu 2+ , Ni 2+ , H + and poly-1-vinyl-1,2,4-triazole-Cu 2+ . The constants for metal binding were calculated. An anomalous distribution of metal ions between the polymer molecules was found to occur in the case where the complexing constant increases with extent of bound metal.

Sedimentational-diffusional and viscometric studies on solutions of poly-m-phenylene isophthalamide and the equilibrium rigidity of its molecules☆

Abstract: The transitional diffusion, sedimentation rate and viscosity of DMAA solutions of poly-m-phenylene isophthalamide fractions in the range MSD = (4·3−305) × 103 with various LiCl contents were studied at temperatures of 273–332°K. The equations SO = 0·88 × 10−15M0.43 sec, DO = 0·71 × 10−8M−0.57 m2/sec, [η]=1·30 × 10−5M0.84 m3/kg and the value of the hydrodynamic invariant AO = (3·55±0·05) × 10−17J·deg−1mole−13 were obtained for solutions containing 3% LiCl, also Δln[η]ΔT = 0·0018 K−1, the length of a Kuhn segment A = 4·5±0·2 nm and the degree of hindering of internal rotation, σ = 1·5. The decrease of [η] observed with increase in LiCl concentration is described by the equation [η] = [η]∞+0·224 × 10−5 MSD·cLiCl−12. With cLiCl→∞A = 3·5 nm and σ = 1·3.

Calculation of the glass transition temperature of network polymers and determination of the chain fragment between crosslinks

Abstract: A calculation scheme for determining glass transition temperature Tg has been developed, based on the chemical structure of the network. This scheme has been verified for a large number of polymers of different structures and good agreement obtained with experimental data. At the same time, a method of determing the molecular weight of the chain fragment between cross links, based on the chemical structure of the network and the Tg found by experiment, was proposed and checked.

Influence of the mode of carbon black distribution on the electrical conductivity of the binary blend of polymers

Abstract: A study has been made of the electrical conductivity of a composition based on polyethylene, polyxymethylene and carbon black in relation to the mode of carbon black distribution in the system. Preparation of the composition by dilution of the polyoxymethylene—carbon black master batch with the second polymeric component, PE, is accompanied by localization of the filler at the interface between the components. This results in the filler forming a conducting network, and gives high conductivity levels at only a low carbon black concentration.

Flow birefringence and viscosity of chitosan solutions in acetic acid of various ionic strengths

Abstract: Chitosan solutions of different ionic strength I were studied, using viscometry and double flow birefringence. The MWs of the samples used were in the range 1 × 104–5 × 105. A linear dependence of intrinsic viscosity on chitosan concentration in a 100 fold range of I was observed in iso-ionic solutions. The characteristic viscosity is a linear function of I−0.5. Folding of the molecular chain during polyelectrolyte swelling causes 2–3 fold increase in the optical anisotropy of the segment, which is explained by an increase in the length of the Kuhn segment. In the solutions studied, the chitosan macromolecules have a swollen coil conformation, the dimensions and rigidity of which are determined by the magnitude of I.

A conformational analysis of polyunsaturated molecules in solution. Continuum model

Abstract: A method has been proposed for the study of the conformational properties of complex polyunsaturated hydrocarbon molecules and of fatty acid methyl esters, based on a model of atom-atom potential functions. An algorithm for chain regeneration by the Monte Carlo method in a model with a continuous spectrum of conformations has been constructed, taking account of details of stereochemical structure, correlation and retardation of internal rotations and excluded volume.

Interaction of protein molecules with a linear polyelectrolyte in solution

Abstract: The polarized luminescence method was used to analyze changes in the synamic properties of protein (lysozyme) molecules interacting with polymer chains of polymethacrylic acid in water and in water-salt solutions and participating in processes of complex formation. The irregular mode of distribution of protein molecules between polyelectrolyte chains is shown: some parts of the polymethacrylic acid are compactly filled with protein, while other parts remain unfilled. Conditions of protein-polyelectrolyte complex formation have been determined ,as well as structural particularities making for greater stability of these complexes.

Structure of non-ordered regions in linear polyethylene lamellae☆

Abstract: Using X-ray diffraction and wide line NMR the authors have studied samples of linear PE with M = 7 × 104 and 106 obtained either by rapid quenching of the melt down to −95°C or lengthy crystallization at +120°. It is shown that depending on the conditions of crystallization of the samples and the MW the non-ordered (amorphous) interlamellar layers contain 20–50 of regular folds, the fraction of long irregular loops is 15–20% and the number of communicating interlamellar molecules with a variable degree of coiling ranges from 20 to 60%.

Modelling of the structure of polyunsaturated macromolecules

Abstract: For the study of the properties of unbrached molecules of polyunsaturated hydrocarbons and methyl esters of fatty acids with discountinuous methylene-double bonds, 20 fragments containing 5–7 atoms in the main chain were chosen and diagrams constructed for their conformational energy. The calculations were performed based on a model of atom-atom potential functions (taking account of the non-valence interactions, torsional and electrostatic terms). An analysis of the conformational diagrams and the experimental data leads to the conclusion that it is expedient to take account of the continuous conformational spectrum, during the modelling of the conformational properties of molecules of this class.

Thermotropic liquid crystalline polymers in electric and magnetic fields. Review

Abstract: The basic concepts of the electro- and magneto-optical behaviour of polymeric liquid crystals are examined. An analysis is made of the main experimental evidence making it possible to discern two main trends in the development of research into the influence of the external fields on liquid crystalline polymers: effects found in polymers and peculiar to low molecular weight systems and processes due to the polymer state of liquid crystals. Possible ways of making practical use of liquid crystalline polymers as media (film materials) with regulated optical characteristics are discussed.

The effect of annealing on the mechanism of plastic deformation of oriented polypropylene

Abstract: A study was made of the extent to which the annealing of crystalline polypropylene influences mechanical properties of PP and morphological features of plastic deformation on stretching. Deformation of oriented samples annealed at temperatures close to the melting point takes place via the formation of specific microcracks (crazes). Plastic deformation without loss of soundness of the material predominates in the unannealed samples of oriented PP and in those annealed at low temperatures. The prevalence of one or other of two possible deformation mechanisms depends on the supermolecular organization of the crystalline oriented PP which changes in the process of annealing.

Multiplicity of relaxation transitions in butadiene—methylstyrene copolymer

Abstract: Ten relaxation transitions were detected in the butadiene-methylstyrene elastomer above the glass transition temperature. Two high temperature transitions are associated with chemical processes of relaxation of SS crosslinks and CC bonds. The activation energies are equal in the case of the first five γ-relaxation processes, and are related to breakdown of various types of bulky physical nodes formed by butadiene units. The next three relaxation transitions are assigned to γ-processes with a high activation energy, and are associated with decay of physical nodes formed by segments containing styrene units or mixed units.

Effect of grafting the initiator to a solid phase on the elementary reactions in radical polymerization

Abstract: The elementary reactions in radical polymerization on the surface of a filler which is also the carrier of the active initiating sites have been studied. Mono- and dicarboxyl-containing peroxides have been used to activate the surface of chalk particles. It is shown that the decomposition of the initiator, the initiation efficiency, chain propagation and termination and the amount of polymer grafted are determined by the characteristics of the grafting of the initiator and by the physical state of the polymeric envelope formed.

Anionic non-equilibrium copolymerization of hexaorganylcyclotrisiloxanes with polar substituents at the silicon atom

Abstract: The authors have studied the anionic non-equilibrium copolymerization of the cis -isomer of 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane with pentamethyl-phenylcyclotrisiloxane and pentamethylvinylcyclotrisiloxane. It has been established that a most important role in the polymerization process is played by the nature of the cyclosiloxane and not the growing macro-anion. Using statistical methods combined with the data obtained from the PMR spectra the authors determined the parameters of copolymerization and the structure of the copolymers. The adequacy of the mathematical modelchosen (first order Markovian chain) to the real process made it possible to obtain quantitative information on the structure of the macromolecular chains of the copolymers at any stage of conversion and for any composition of the initial comonomer mixture.

Effect of the conditions of synthesis of polymethyl-methacrylate on the heat of polymerization

Abstract: The heats of polymerization of methymethacrylate in bulk and in various solvents have been determined by the joint use of the methods of calorimetry and ozonolysis and the structural features of the polymers obtained have been investigated by IR spectroscopy. It has been found that the heats of polymerization are higher in solution than in bulk and vary with the nature of the solvent. It has been shown that the excess heat evolution is caused both by specific interaction between the components of the solution and also by aggregation of the macromolecules through the linking of CO groups into stable associates. The splitting of the valency vibration band of the CO bond in the IR spectra of PMMA is evidence of the existence of associates of this type. It is incorrect to use the standard heat of polymerization of methylmethacrylate in bulk to study the kinetics of polymerization in solution and it is necessary to determine this quantity for each specific system.

Study of the initiation mechanism of post-radiation graft polymerization of vinyl monomers on solid inorganic materials☆

Abstract: ESR was used to study the type of active centre of silica gel exposed to γ-radiation. It was shown that at 20°SiO type radicals are the main initiating centres of polymerization on silica gel exposed to γ-radiation. When carrying out post-radiation graft polymerization of methylmethacrylate on silica gel exposed to γ-radiation high degree and efficiency of grafting cannot be achieved. As a result of the treatment of silica gel and macro-porous glass using chlorosilanes the concentration of active centres formed by the action of γ-radiation can be markedly increased and the yield of graft polymers and the efficiency of grafting, raised.

Some problems in the synthesis of polyphosphazenes and possible solutions. Review

Abstract: The review generalizes the published findings and the authors' own results on some general problems concerning the synthesis of high molecular weight polyorganophosphazenes with an open chain, in particular, problems of the initial polydichlorophosphazene and the unit heterogeneity of the macromolecules of the polyorganophosphazenes resulting, in the main, from the hydrolytic instability of the PCl bonds in the phosphazene structures. From analysis of the published experimental findings obtained by various investigatirs it is concluded that an important distinguishing feature of the polyphosphazenes is the high sensitivity of their properties to insignificant amounts of anomalous units which practically need not be considered for most other polymers, and which are commonly called traces. By virtue of this feature of the polyphosphazenes the successfuls solution of the problem of their synthesis and obtaining stable well reproducible results calls for a scientifically based approach to the control of the secondary processes of hydrolysis. Some of the possible lines of such an approach have already been identified and are considered in the present review.

Conformations and dipole moments of poly(methyl) methacrylate molecules

Abstract: Local conformations of stereospecific PMMA chains have been investigated. For these chains and for atactic PMMA we calculated the mean square dipole moment 〈μ2〉 and the correlation factor g=(μ/nm2)n→∞. In the case of isotactic PMMA chains the share of tt conformations amounts to 75% of the monomer units, and in the syndio chains the amount of tt conformations is increased up to 90%. Vaues of g calculated for the isotactic and atactic chains over the entire interval of values permissible for the energy parameters that may be reconciled with experimental findings are obtainable only if it is assumed that there is a regular alternation of the directions of dipole moments of side polar groups (pendants), the rotation angle being x = 0 and 180°; in the syndio chains the probability of there being an alternation of the directions of dipole moments of the pendants 12

Compositional inhomogeneity and other molecular characteristics of chlorinated polyvinyltrimethylsilane

Abstract: The light scattering method, GPC and viscometry have been used in a study of various molecular characteristics of chlorinated polyvinyltrimethylsilane (CPVTMS) containing differing Cl concentrations and prepared by photochemical chlorination of CPVTMS by molecular chlorine in CCl4 solution. The compositional inhomogeneity of the CPVTMS according to the chlorine content proves to be small. The data on change in the molecular characteristics of PVTMS during chlorination show that the process is a polymer-analogous reaction accompanied by occasional but rare acts of rupture and crosslinking of main chains of the polymer.

Some problems of the theory of polymer-analogous and intramolecular reactions of macromolecules. Review

Abstract: A review of the current state of the theory of macromolecular reactions is presented It looks at the methods of calculating the kinetics of polymer-analogous and intramolecular rections and the statistical properties of the products formed and also the methods of solving back problems—evaluation of the kinetic constants from the experimental data

The phase composition of polyblock block-copolymers of polyarylene sulphonoxide and polyethylene oxide☆

Abstract: Temperature transitions were studied in 3 series of polyblock block-copolymers of polyarylene sulphonoxide and polyethylene oxide, prepared by various synthesis methods. Composition diagrams were constructed and the phase composition analysed. The phase composition of these copolymers was practically independent of the synthesis conditions and the nature of the chain extender. The composition diagrams were qualitatively similar to those for other block-copolymers with a close ratio of component solubilities. Depending on the composition, the formation of single phase solutions, amorphous-amorphous and amorphous-crystalline layering was observed. The relation of crystallization rate and melting point to composition and the dependence of morphology and behaviour during uniaxial stretching on composition is discussed.

Effect of tensile stress on the molecular mobility of oriented amorphous-crystalline polymers☆

Abstract: ESR spectroscopy was used to study the effect of dilatational strain on the molecular mobility of uniaxially oriented PP and PE of high density and varying width of MD, which are oriented to varying degrees in elongation. For slightly oriented PP and PE samples it is typical to observe increased mobility in the elastic zone, the effect decreasing with an increase in orientation. For highly oriented samples segmental mobility decreases in the whole section of elongation. The dependences observed are explained on the basis of ideas concentraning the volumetric variation of the amorphous phase during elongation.

Cationic copolymerization of glycolide with dl-lactide☆

Abstract: A study was made of kinetic regularities of copolymerization of glycolide with dl -lactide in melt in the presence of ZnCl 2 and SnCl 2 ·2H 2 O as initiators. Glycolide is much more active than dl -lactide in copolymerization ( r = 4·6 and 0·3, respectively). The type of initiator and activation of the process with hydroxyl-containing compounds have no effect on the relative activity of monomers. A study was made of the dependence of melting point, glass temperature and the heat of melting on copolymer composition.

Rheological behaviour of melts of a thermotropic mesomorphous polyester

Abstract: It has been established that the rheological properties of melts of a thermotropic liquid-crystal polyester with a mesogenic component in the main chain are largely determined by the specimens' previous history. With standard preparation conditions, it has shown from comparative experiments that there exists for each polyester a region corresponding to the smectic state, from which the polyester can undergo transformation into the nematic, isotropic or a mixed state. The flow characteristics of the polyester melts enabled them to be classified as plastic bodies. The experimental data obtained may be explained in terms of a proposed phenomenological model of the domain type with ligaments in the form of interlinking chains.